HOW TO: pick the right carburetor. SIZE MATTERS!!! Don't overestimate, do the math.

[@johnparker1787]

I have to say you never know till you try, I ran a 1475 cfm Holley gen 3 carb on a 454, it ran great. So I believe anyone can say anything. Test and tune

[@MyKARSShop]

Thanks for watching I elaborated on this more to clarify where I was coming from in a recent video. kzbin.info/www/bejne/oIHQmKWol76kqrMsi=jrtL7g34g169QhQf

[@danandsveaadventures3834]

Good job explaining both the math and physics involved… you could do some stand-up comedy shows also… keep up the good work…

[@MyKARSShop]

Thanks for watching. I try to keep it interesting… even if it’s a bit corny. Lol.

[@chadwb7079]

One thing I might have missed, but single plain intake vs. Dual plane intakes makes a big difference on CFM.

[@MyKARSShop]

This video is not about how an intake affect flow, but rather about the actual mechanical ability of an engine to flow outside of intake and carburetor. There is another video on the channel, and we should clarify exactly where I’m coming from on this, because this video was several years ago, and was addressing specific questions at the time. kzbin.info/www/bejne/oIHQmKWol76kqrMsi=9BTzwmf_oIwBkyJp

[@teemic3019]

and port cfm just because it is math does not mean it is right

[@edwardmylnychuk5774]

thanks for this info, when i was younger i had a 302 with a stock 2 barrel so i though he lets get a bigger 2 barrel carb and get more power, did not make a difference that was very noticeable

[@MyKARSShop]

Thanks for watching

[@edbrown1080]

Also a single plane intake won't tolerate near as big as carb as a duel plane specially on the street.

[@venjhammet]

Thank you for making me understand how to calculate for the correct carb to use. I have been trying to figure out what to pick the correct carb for my bike. Now I have a clear picture. Thank u so much

[@MyKARSShop]

You are so welcome! Thanks for watching!!

[@antisocialsecret7584]

Cam grinders give you all the info for that specialy cam you want. Like how much carb, intake, ported heads, stall..gears.

[@MyKARSShop]

Good information. Thank you for watching.

[@tools6106]

Having owned a 4valve ford, it ran a very high VE of 93%, hemispherical chamber. Measured at under 600cfm, so the math is accurate!

[@MyKARSShop]

Appreciate the encouraging words. It’s definitely been a very controversial video. Most of the time the one thing people leave out of the equation is how drivable it is through all of its ranges. And that’s where the video was coming from Good to hear that your experience lines up with math. Awesome to hear from you. Thanks for watching.

[@HSPOVgames]

Divide by 3456 because there is one intake stroke per 2 revolutions of the 4 stroke engine.

[@MyKARSShop]

Thanks for that.

[@rono3045]

You're wrong buddy... I put a 1050 Holley double pumper on a 351 Cleveland with 2v heads and shaved 2s off my quarter-mile time that's all I did you want to know why it got faster the holes in the base plates are bigger than a 650 or 750 more Air..

[@craigbenz4835]

I always sized carbs the way you describe, but one time I was in a bind. I replaced the Holley 650 vacuum secondary carb on a tight but mild 440 with a Holley 800 spread bore double pumper on what was supposed to be a temporary basis. The car ran better on the street and the strip, so I never went back. I don't have an explanation.

[@jamesspain5049]

Your post is older but dual plane intakes you can multiply what recommendations on size they have to 50% larger

[@cuzz63]

Spreadbore...

[@KingJT80]

@@jamesspain5049 x1.1 instead of x.85-.90

[@mikesauer7775]

Totally agree that for street use smaller carb always runs smoother..But...Dyno numbers and dragstrip mph show specially tuned 950cfm will make slightly more power everywhere above cruising speeds on your typical 450-500hp 383cui.. not talking drivability

[@markmccarty9793]

Also assuming that on a vacuum the back barrels are fully open! You can bandade a 750 to run on a 5 liter and actually get decent milage. Get the kit to change the secondary springs, a 50cc pump and a selection of shooters. But, it's still a Holley!!

[@cuzz63]

There are plenty of Dyno tests showing that a 650 will support up to 500hp motors with only slight gains by larger carbs.

[@markparker5788]

For the first time in my life, mines too big. Lol Thanks for the education Mike! RAWK!!

[@MyKARSShop]

😂😂😂

[@paulthompson1654]

A good ve comes from a good cam bigger than stock with at least 11to 1 compression . Great carb , intake manifold ,, CNC cyl head ,,, headers that fit the ports ,,, 100% ve will occur some times

[@MyKARSShop]

Exactly what I was saying. 100% VE is not the norm unless you absolutely know what you Love your comments! You completely get where I’m coming from Thanks for watching

[@adam8888d]

I have Asbergers. This video makes more sense to me regarding carburetor sizing than anything else i have seen on the web. I bought a 390gt mustang that has a 750cfm carb. The engine runs well but i am thinking the engine will run better with a 600cfm that i have ordered this morning as the secondary vacuum is not working. Everything has been checked and i have also fitted the lightest spring. I guess the engine is unable to open the secondary vacuum due to the carb been too big.

[@MyKARSShop]

I’m glad you found the video helpful. These calculations are targeted more towards driveabke good performing street cars… I hope you find the new carb beneficial. Let me know how it goes please! Thank you so much for watching. I hope you enjoy the channel

[@JeffreyFank]

I have a Pontiac 428, had to bore .060 over because of cylinder scaring. My professional, lifetime experience engine builder said my 650 was too small. Ihe suggested a Holley 750 double pumper. It’s a street rod not race car.

[@MyKARSShop]

You may find the second video I did helpful Thanks for watching! 😎 Revisited! HOW TO: pick the right carburetor. SIZE MATTERS!!! Don't overestimate, do the math. kzbin.info/www/bejne/oIHQmKWol76kqrM

[@paulthompson1654]

Calculate air flow for cubic inch and max RPM and volumetric efficiency V/E Holley recommends for naturally aspirated 100% ve for most performance . Race only 110% ve . If the carb is to big it will not meter the fuel as well due to lack of vacuum signal . Once the engine is on the dyno the vacuum measured at full throttle should be .5 in hg to 1.5 inhg .

[@MyKARSShop]

Good information. Thanks for sharing.

[@Notyourdaddystoast]

Currently have a Ford 460 running a 750 carb with vac secondaries. Runs great

[@MyKARSShop]

Thanks for watching

[@markkramer7068]

You have a good sense of whats going on, i truly believe your leaning more towards novice or younger car enthusiasts so that may be where you get a little kick back from more experienced hotroders . I as a person who have owned mech shops always had to know my customer who wanted to beefup their cars performance .what could they handle most were clueless so i did little perks if they wanted more i added to it. But most just wanted to drive around look cool and rarely if ever get on it. So your pretty correct in how you presented your video. Talk more about HP that the engine truly has as per CU , 6pac other types of carb manufacturers, how to ajust cards for proper air flow . Waiting for your next video. Oh rear end gearing per HP also. Open to posi rear-end.

[@MyKARSShop]

Thank you so much for your comment. I’m sorry I’m so slow in responding. Just super busy this time of year. You exactly were picking up what I was putting down I actually did two more videos on this to explain where I was coming from. But you nailed it exactly exactly. I was approaching this from the point of drivability and street performance, not maximum performance at wide open throttle. Having spent many years running cells, I am fully aware that performs well on the Dino and the dragstrip will not necessarily equate to a street car Awesome. Thank you.

[@adamh1889]

Smart guy+ dry erase board = me feeling dumb. Good video I haven't felt math anxiety in years, all jokes aside thanks for giving your time youtube university salutes you

[@MyKARSShop]

I’m not all that smart… Lol but I share what I know. Doesn’t mean that it’s right, but it’s what I know. Thank you so much for taking the time to watch. I truly appreciate it.

[@JohnRocks6368]

Gotta love all these calculations and they are probably good for a starting point but there are too many variables. A stock 350 sbc might only need a 600 cfm carb, start adding better intake, heads, and most importantly cam lift and duration, and you are going to need a bigger carb. There's a lot of carb tuning involved with any sized carb so saying I ran a 750 then replaced it with a 650 and it ran better doesn't really mean much. It only means something if both carbs were really optimized. If you can somehow get to a dragstrip you can actually do some real world testing and find out what works best. I happen to run a 750 Holley double pumper with a 50cc front pumper on a 1968 Camaro 383 sbc chevy engine, automatic with a Vega converter (about 3k stall) 2.05 heads and 538 lift cam - car runs mid 11's (11.62 best so far in 1/4 mile). I wouldn't hesitate to try an 800 cfm and see if it's better after going through some tuning on it. It's the only way I'll truly know.

[@tech270154]

Your video is fantastic,i don't work anymore on cars because of my health but i enjoy very much all the lectures .I want to know in the formula how do you know how high the rpm will be before you do a dyno test so you can achieve the formula right ? thank you

[@MyKARSShop]

The primary limiting factor is going to be here cam profile - so look to your manufacturers specs for that How you install the cam and a great also has some bearing. Glad you enjoyed the video. Thank you for watching.

[@Ratridez]

All depends which carburetor , you can go much bigger with a spread bore and still streetable .

[@davelowets]

But at WOT, a carb that's too big still is NOT an advantage. Do the math, get the correct size for your engine, and do NOT try and crutch it. I drive a car with an 1150cfm Dominator on the street, and it's the correct size for my 547", 7300rpm, big block. And guess what?? The throttle response is super crisp, it doesn't load up at idle, the plugs look perfect after stop and go traffic, it starts with 2 pumps with no choke, and it works just fine. It doesn't need to be a spread bore, or crutched in any way to work perfectly. Just get the correct size, and you'll have no issues.

[@edbrown1080]

Most vacuum secondarys with stock springs on street smallblocks won't open all the way=smaller CFM.

[@MyKARSShop]

Exactly. A fact I have said repeatedly, but most people want to ignore. Lol thank you for clarifying that and reaffirming it. Thank you so much for watching.

[@davelowets]

Then you need more motor....

[@davidtaylor5082]

Thank you for the great explanation of this I have seen some confusing videos on this and your video makes sense bye the math I have a 650 on my engine and it calls for a 653 so I hit it perfect I’d rather be a little bit smaller than over carbonation so I won’t wash out the rings and everything else

[@MyKARSShop]

Glad it was helpful! There is another video on the channel in which Aydell further into the background behind this one… You might also find that one encouraging. But I’m glad the numbers added up for you. Thank you for watching kzbin.info/www/bejne/oIHQmKWol76kqrMsi=9BTzwmf_oIwBkyJp

[@marccres6619]

We did this at the engine shop came out to be a 650 cfm ran it then a 750cfm and made more hp with the 750,put a 800 and did even better but lose a little at the bottom end.

[@chrisbusch1970]

that's because this calculation is BS

[@KingJT80]

@@chrisbusch1970 its not. you forgot the VE part. it made more because the engine they put the 750 on is more VE thats why the 750 outshined the 650

[@paulthompson1654]

The worst situation is an oversize carb with being a double pumper with low stall and stock diff gears

[@MyKARSShop]

Exactly my point. When I shared this video, I wasn’t clear that I was talking about street cars. I’ve done a couple other videos to try to clarify where this was coming from. I think I changed the iCard links to reflect those videos Would love your perspective on them Thanks for watching

[@charlesnewman3875]

People need to understand something basic about a CFM rating for a carburetor. It is a capacity and not a supply number. In other words the carburetor is not a pump but rather a valve. As the formula is showing an engine that can pull/call for "x" number of CFM. Basically the carb isn't going to "shove" or over-feed CFM but rather the engine is going to "draw" "x' amount of CFM based on cylinders, heads, pistons, and rpms. We could throw the manifold in there but for simplicity sake of the discussion you see where this is coming from. The carb is sized by the manufacturer to have certain dimensions of open space and size of the butterflies to coincide with a certain sizing of fuel metering in order to get an atomization figure that is efficient across a CFM flow range. You can plunk a 600 CFM carb on something and maybe it will be on a motor that will only ever try to draw 500 CFM max. You could conceivably re-jet/meter that carb for smaller fuel flow and be fine. My point is that there is a great misunderstanding about how a carb functions and what it is actually doing. When people say they have a 780 dual feed on a stock 5.0 ford and it seems to run fine it may very well be the case but not because the engine is calling for 780 CFM when it's cranking 6000 rpms but rather because the air/fuel ratio, atomization and quantity is OK for the other factors of engine performance and is not loading up the cylinders. There is after all an efficiency of combustion to take into account long before we worry about 600 or 850 for CFM figures on a carb. Most people do overcarb from a capacity standpoint which is quite different from a supply standpoint. Thought of another way if you put air flow monitoring between the carb and manifold on a 5.0 Ford and the carb was an 850 you might be astonished at the fact it might only be measuring a flow of 400 or 500 at 6500 rpms because that's all that it is trying to suck into the engine and the carb is not limiting it certainly but it has no ability to try and "over feed" CFM. As I said as long as the fuel/air is OK you not be overloading the engine on a CFM basis. Biggest mistake people make is not understanding what is actually happening with an engine. I don't care if a carb is rated for 2000 CFM if the running engine is only calling for 500 then that's it in a NA engine. The same for heads. They may have a flow figure that is way higher than what the cylinder as configured can, or needs to, pull through them. You see guys with huge flowing heads running around on the street and they don't understand that the heads they paid huge money for aren't even approaching anywhere near the flow limit even when they're at wide open throttle. You start in the cylinder and it all follows from there.

[@MyKARSShop]

Very well said. I actually circle back around to this and there’s another episode to qualify the context from which I was sharing this. Thanks for watching. And thanks for your comments. Very well stated.

[@trailerparkcryptoking5213]

The carb flow is rated at a certain pressure drop across the carb. This basic volumetric calculation doesn’t account for this. There is a video on KZbin that covers a more real world method for determining carb size. That’s why several commenters have had success with bigger carbs than this basic theory recommends..... This can be a basic starting point, but pressure drop across the carb is a dynamic situation and constantly varies. I haven’t spent dyno time, but been tuning carbs since I was 16 years old and have had fluid dynamics class in engineering school. I had DaVinci change the IFR’s and install downleg boosters in a 3310 VS for a street driven BBC in my ‘72 C10 and it flowed 830 cfm. He ran it on a sbc test engine and got it tuned in. I get it home and put it on my big block and it has a massive hesitation when you stomp on it. Seemed like a lean stumble so I pulled the VS spring to find it was one spring from being the weakest spring in the spring kit. I put in a spring one away from the strongest springs and now VS kick in slower. When you hit it now no hesitation and the old truck jumps sideways .... DaVinci’s test engine isn’t under load and VS’s have to be tuned under load. Even the experts get it wrong at times....

[@teemic3019]

you are right this math is a joke . i have seen a stock 305 sbc make the best hp and torque numbers on the dyno with a 950vs and it still had 1.2 hg of vac at full throtle .

[@earlfreimuth5799]

If you are right Why did GM use 800 cfm quadrajets and Mopar put 6 pack on 340 🤔

[@MyKARSShop]

Air door, carburetors, and vacuum secondary carburetors only flow what the engine requires. I Elaborate more on this in my second video on this kzbin.info/www/bejne/oIHQmKWol76kqrMsi=XNH9-MpEQLSGrh1b

[@heshtesh]

I always find this issue interesting due to the fact their are so many variables involved. I run a 94 Sonoma on the street with a 10.7 to 1 1st. Gen 399 stroker with 17* heads with 261cc int.runners that I believe most would consider way overkill for the street. My combo features a 4l80E w/3000/3200 stall with balloon plate and 9" with 3.55 gears. On the dyno w/89 pump gas the engine did 266 hp and 400 ft lbs@3500.....440 hp and 513 ft lbs.@4500......608 hp. and 560 ft lbs@5700 max tq. ..........641 hp. max and 526 ft lbs.@6400. The reason I point these #'s out is the fact my engine does not studder or shudder or cough or eat plugs it just runs as smooth as could b with a QFT 950 Black Diamond on the street and I honestly don't believe there's a chance in hell a 739 cfm which is the size carb recommended for my cubic inches could support any of those #'s except at the lowest power levels. Cam/ 260/266@50....679/669...110 split solid roller. Heads flow 404 cfm. What is your opinion?

[@MyKARSShop]

The volumetric efficiency of your engine is obviously much greater than the numbers I’m using here in this video fir mild street performance. . I’m glad you found a combination that really works for you

[@heshtesh]

@@MyKARSShop Thanks i'll let the 2 guys who built and dynoe'd the engine know , I bought every thing as an assembly project so take no credit for their skill set. I am now going to take a little time to learn more about volumetric efficiency in a N/A engine.

[@davelowets]

If your heads flow 404 cfm's, you SHOULD be making 800 horsepower. Something is very wrong with your setup. Edit: By the way, I've had a 750 carburetor on a 700+ h.p. small block. Dyno proven.

[@heshtesh]

@@davelowets The heads should be able to support 800+hp but that would require help in the form of higher compression(approx 15 to1) and a significantly larger camshaft, i'd toss in a 1050cfm to go with it. This is a street engine not a valve train beater like a 800-900+ lift cam engine would be. Please note this engine is done at 6400 rpm., wonder where it would be with a cam making power to 8500+ with 15 to 1 ?

[@KingJT80]

@@heshtesh that has a lot to do with it. 800HP CAPABLE but yo spin it to x RPM lower than whatever it take to make 800

[@TheThirdWheel618]

This is great there are so many opinions out there especially on the aftermarket parts reviews jegs / Summit /Forums and alot of them are wrong. I Iisten to too many and it cost me in the long run I have read put 750 nothing less i would rather be over carb than under carb . Intake manifold as well i have a Ford 390 truck engime 9:1 compression truck heads puller motor basically i wanted to go from a 2bbl to 4bbl i bought the cast iron boat anchor intake then read all.the jegs and summit and forum guys saying ditch that boat anchor ⚓ get a Edelbrock but dint get the perfomer thats just wieght savings yiu will never hit 5,000 Rpm with a regular performer you want the RPM performomer . Ok so i listen to them that thing was a beast the runners were huge compared to stock anyone work on a 390 Ford ? The pushrods go down through the intake first drive i was not impressed i had actual better performance with the stock 2bbl and 350 cfm Holly . The low runners gave me tons of tourqe and mid range power matched with the bigger base plate 350 2bbl if flowed better at take off and cruise . The high runners of the RPM needs heads that flow well to match and i woukd nevef hit anything over 4,800 with that stock crank the Gt 390.was rated at 4,800 RPM sure it runs good but in this case i think it woukd run way better with the regular eddy or even the cast iron 4bbl all because the internet new better see the price of thst thing lately ? A eddy performer RPM is pushing 700 bucks thanks guys 😮 whew had to vent ....

[@tonycolca2241]

Very good presentation thank you!

[@MyKARSShop]

I’m glad that it was concise. It just provides a baseline, I have another episode coming out sometime in the next month for a revisit this issue. Trying to clarify a lot of the misunderstandings people have walked away from this with. Thank you so much for watching. I hope you enjoy the channel.

[@tonycolca2241]

@@MyKARSShop formulas for determining the correct size carb are very general. Unfortunately thr only real and thorough way is a chassis dyno because it puts load on the engine from start to finish.

[@davidwellman7080]

Im still confused, I had a 71 Cutlass bone stock and i bought it from the original owner. 350/350 turbo transmission. It came from the factor a single pumper 750 carburetor. Would that formula go out the window. I know that by the build sheet and I had to get the carburetor rebuilt and the old man told me that when he worked on it.

[@MyKARSShop]

Factory basically used only a couple of size carburetors that was to keep manufacturing costs lol. But these carburetors were fairly universal. But these were not intended to be performance carburetors. They were the one size fits all for multiple applications Whole the maximum flow of the carburetor might have been 750 CFM, that is not necessarily what the engine needed or used. D The genius of a spread bore carburetor like General Motors used is you had a good throttle response at the low end? And then an on demand, secondary with an air valve plate, that would only feed with the engine what it asks for So, while the carburetor might have flowed max 750 CFM The engine itself might only require 400 CFM. These air valve door, carburetors, Quadra jet, thermal, quad, etc. are much different than a Holley because they were spread bore with small primaries and large secondaries. Holley carburetors in general were square flange carburetors… meaning primary and secondary’s use the same size throttle bore They did not use an air valve door Although the vacuum secondary Holley carburetors function in a similar way, They had much larger primary bores I did another follow up video on this subject to explain things more in detail Here’s a link. Hopefully this will help shed more light. Thank you so much for watching kzbin.info/www/bejne/oIHQmKWol76kqrMsi=8HnoHxHNS8o5REwp

[@Geezer1320]

One things for sure, our cylinder heads and camshaft technology have come a long way from what it used tho be. But I agree with you that most people over carb their rides. How many classic rides have you seen at a car show that the fumes from being over rich chokes you out?

[@MyKARSShop]

Exactly. People don’t understand the difference between building a full on race car and building a Street Kar. I actually have another episode coming out sometime in the next month revisiting this topic. Thank you so much for watching

[@cuzz63]

the carb being rich isnt because its oversized, its because they dont know how to tune the carb.

[@KingJT80]

@@cuzz63 its because manufactures put out different sized and different TYPES of carbs that are all jetted different different venturis etc . and if you look at what they recommend for what it is youre doing, you'll see most people pick the wrong one and then it runs the way it runs vs just using the MORE CORRECT ONE for the application. a 750 holley on a stock 350 will work if you tune it, youre right. but the main point is why would you do that when you could have just bought a 500 CFM and not be messing around with it or messing with it way less and enjoying the car more? could i put a 1050 dominator on my engine when i rebuild and stroke it to a 6500 RPM 331 ? sure but maybe i should just buy the edelbrock 650 AVS2 or holley 650 vac secondary for it and ill have less headaches with trying detune the carb down to what it is i actually have going on

[@cuzz63]

@@KingJT80 your preaching to the choir....totally agree. I have seen time and time again on Dynos where a 650 will make close to the same power as a 750 on motors under 500hp and yet so many guys think they need a 750 on their 400hp motor.

[@teemic3019]

That is not over carbed that over jetted over carb would be lean because of to big a hole letting in to much air ! over carbed is lean because the air moves so slow it does not cause enough pressure drop to pull fuel from the bowl !

[@dedreman2227]

This formula will give you the smallest option carburetor. A step or two above the size carburetor this formula gives you is the one to go with.

[@KingJT80]

then omit the VE and just do 100% then. just rememeber you MAY have to tinker a slight bit more with it and mechanical secondaries REALLY need to be precise vs vacuum secondaries

[@jakeblack4095]

What is the difference between a stick and a manual?

[@MyKARSShop]

You raise a very good question A manual can mask too much fuel to a point / because the engine can get to WOT where an automatic might bog However. Correct carb sizing will perform well in both scenarios At the end if the day, It’s really all about what you’re shooting for. I don’t mind over carbing as long as I know the trade offs. There’s another video that I recently rehearsed where I revisit this. You might find it helpful Thanks for watching!!!

[@ryanpaasch7464]

I have built 360 put 625 Carter it would not run well put 750 holly vacuum secondaries ran great surprised us

[@einstein3509]

Well, I know this math and used this math. But it seem when you use a Dyno and experiment you find that on a 355 or 383 stroker pushing around 450hp and up at around 6500 rpm’s the 750 Holley really shines. The 650 works great but you get more out of the 750 but as soon as you go to the 850 you loose performance. “Watch Engine Masters” Back in the mid 80’s I had a stock 350 with a 2 barrel and a automatic transmission. 72 Chevelle I rebuilt it . All I did was add a performer intake and cam for low end shaved the iron heads 20 thousands. 5500rpm was max and that was pushing it. I installed a 600 Holley double pumper mechanical secondaries. Was thinking I should’ve used a 650 vacuum secondaries. No race engine but I sure had fun with it. So, in my opinion……. I think that calculation works great for stock or mostly stock engine and not so much when you are push 450hp and up. I use that calculation as a good starting point.

[@MyKARSShop]

I think that’s where that volumetric efficiency number comes into Great feedback. Thanks for watching.

[@KingJT80]

yeah more to do with VE here. and is the car faster down the track? the dynos are one thing and mostly for making sure things are what theyre supposed to be but the meat and potatoes is the track....

[@adrease1112]

Please help i have a 347 stroker with 830 cfm is that to much ??

[@MyKARSShop]

Not enough information. Horsepower? Maximum rpm? Use? Compression ratio? Cam size? If it’s a mild 347 stroke or that I would say yes. It’s too much carb. But if it’s super performance… That’s where the volumetric efficiency number comes in to play.

[@ktr831]

Makes sense but why does gm recommend a 750 on their 350 zz crate motors?

[@MyKARSShop]

I actually have a follow up video coming out on August 22… It might shed some more light on this Thank you so much for watching and taking the time to comment. Much appreciated.

[@kevinscott5648]

Hi. Thanks for putting up this video and other content. I just found you today and I'm subscribing! I have a 390 FE Ford big block engine that we're stroking out.. 428 crank and alot bigger cam. Its our first engine to build. Do I kinda guess the cubic inches of what it could be... Or just go with the 390 original size..? I have a brand new 750 Holly double pumper that I have access to.. Would that be fine since we're stroking it out?

[@MyKARSShop]

If you know the bore size of the engine, and the stroke length of the crank, you can calculate the cubic inches. There are plenty of online calculators in which you type in the bore size, the stroke, and the numbers of cylinders, and it will do it for you. Or you can find the actual formula and calculate it Once you know the cubic inches, I would look at cam size and compression ratio and come up with a reasonable VE number, and then find out where you’re at with your carburetor I would consider how it’s going to be used. Is it going to be daily driven, occasionally driven, is it a street performance car, is it a race car You’re probably not far off with a 750 carburetor. But your transmission ratios, potential stall speed of the converter, and rear axle ratio is also play into it. My general rule of thumb is if it’s a daily driver street car, I prefer to have a smaller carburetor. If it’s just a horse around car, I always tend to go a little overboard with my carburetors. If it’s a full on race, car pro, I get pretty stupid with it. Lol. The calculations in the video just help you find a baseline, so you get a ballpark on where to start Hope that helps Thank you so much for watching. Thank you so much for the sub

[@NewEngland462]

What would u consider a 351w. Stock bottom end throw down 370 rwhp and 460 ftlbs threw a c4 trans ve%

[@MyKARSShop]

I don’t have enough information to be able to tell you, but if you go through the formula that I shared, and do the math. I would guess you’re going to end up around 650 CFM on a vacuum secondary carburetor. That would be a good Street driveable carburetor.

[@NewEngland462]

Trick flow 11r. 190 at 56cc heads. Trick flow stage 2 cam. 542/564. 222/234 duration. Port matched vic jr. Made power on dyno out to 6500. With a 750 dp with annular boosters. I was running a 600 double pumper for awhile and I completely agree. Smaller. Well what the masses would say is smaller actually runs amazing. I recently picked up a tapered 4 hole spacer on top that vic jr. A 650 annular booster double pumper and swapped to a t5z with a 410 rear and off idle can blow tires right off. Thinking the 650 great for street. Probably great in 1/8 mile. The 750 maybe take it on a 1/4. But idk. Il see

[@NewEngland462]

That delicate balance of vacuum , fuel suspension and atomization.

[@NewEngland462]

Oh. We got zero vacuum at wot with the 750 on dyno btw. Shorty headers

[@ezkempinkemp3467]

Thanks!

[@MyKARSShop]

No problem!

[@pjimmbojimmbo1990]

A 5 liter spinning 5000, with 80% VE only needs about 385CFM, so even a 600 CFM is overkill. A 454 would be still be less than 600Cfm at 5000 with 80% VE

[@misters2837]

You are 100% right! - This is the #1 WORST thing I see people giving for advice in Social Media Groups...Bone stock 5L to 6L V8 and EVERY ding dong chimes in and says "put a 750 on it"....Look at XYZ Magazine, they used a 750 or 850 on the *DYNO* - yeeeeeeeaaaaaah and the dyno is ONLY run at WOT, do YOU drive thru the Tastee-Freez line at WOT? - Didn't Think So! - They put a 750 on it and think wow it runs GREAT, I get in it and think "wow the midrange on this thing is full of holes!"

[@pjimmbojimmbo1990]

@@misters2837 I like it when they will say they can feel the Secondaries "Kick In". One should never notice the Secondaries opening, if there is bump, that was a recovery from a Leaning out. Also, only Fools will run a Double Pumper on the Street. 99% of Vehicles, even those that run the 1/4 mile on weekends, will do much better with Vacuum Secondaries In 1979, I was listening to a guy telling me how he put an 850 Double Pumper on a 289, and how great it ran. I asked him if he was spinning past 10 Grand. He said no, highest it would go was 4800 before the Tranny would shift. I just told him great, glad you liked it. Idiot

[@misters2837]

@@pjimmbojimmbo1990 (That 289 probably never even Got the Secondaries OPEN!) - I try to explain that the "Primary Barrels" are what is screwing them in the mid range, and they never grasp the idea... The Q-Jet was perfect all around carb, it was put on 252cid V6 and 500cid V8 but it had 200CFM Primary Barrels, and HUGE secondaries that work on any sized engine...Much smaller than the 375CFM Primaries on the Default "750" every ID10T has to slap on their STOCK 302 or 350... ALSO trying to explain that 2bbl an 4bbl CFM are TWO completely different rating systems... I never really got into the Holley carbs, I tried tuning a couple for the street, Not that they are bad, we just didn't agree, I have Carters and Edelbrocks that have been in service since the early 80's that only needed adjustment when this corn gas came out....

[@pjimmbojimmbo1990]

@@misters2837 The 850 I had referred to, was a Double Pumper, so the Secondaries would open even if the engine only needs 50 cfm. I agree about the Q-jet being one of the best Carbs ever engineered, and it's capability to be utilized/calibrated for many engines. As for the 750/780 Holley, cut the secondaries off and you have the Holley 500 CFM 2bbl. It is about the Perfect size for a 5 liter engine. I have used Holleys on my Boat, and on a couple of Trucks, they are okay, but are not easy to calibrate for both Power and Economy. It is easy to calibrate for one or the other, but to get both takes a lot of math, and often drilling of the Metering Block/Plates on the Power Circuit to ensure enough fuel when needed, once the Main Jets are leaned out for economy. That Corn Gas, has been a major F*** Up for a lot of Fuel Systems, plus it is very bad for use in Boats, as it likes to absorb the Water that is in the Air, and that causes all sorts of Grief.

[@arthurcgans8198]

Good info, thank you!!!

[@MyKARSShop]

Very welcome. Thanks for watching. Hope you enjoy the channel

[@pnwoods]

If by chance you still read the comments, ... Picked up a stock '70 LA 318 Dodge W200 Power Wagon, truck gears, Carter BBD 2 barrel.. rarely over 3500 rpm. .. Shop manager, and my mechanic suggested a low rise Edelbrock/w 4 barrel. .. Edelbrock customer service recommended an Edelbrock #1405, 600 cfm. .. Questioned him about the size, .. he validated it. ... the formula points to a 350 cfm. ... Will the 600 be more trouble than it's worth?

[@MyKARSShop]

There are a couple of factors… The first thing is, a vacuum secondary carburetor - when properly tuned, will only give what the engine is asking for. I am surprised they didn’t recommend the 1403 or 1404 over the 1405. Obviously Edelbrock knows their carburetors better than I do. And I have heard rumors that advertised flow is actually higher than the actual flow? But I haven’t had time to dig into that yet. I think with the vacuum secondary carburetor and at the lower p.m. you’re shooting for, you’re hardly ever going to use those secondaries. But it still would probably be a better choice than the factory 318 two barrel carburetor. I have used Holly 600 CFM carburetors on 318s and just tuned the secondaries for optimum performance. (So they only open up enough to give the engine what it wants without overfueling) So it might not a bad way to go Thanks for watching. Hope the answer was helpful. Hope you enjoy the channel.

[@pnwoods]

@@MyKARSShop Input much appreciated. Thank you. Subscribed. .... addendum: ... Looking back, now, it wasn't Edelbrock's customer service, ... it was Jegs customer service tech. Jegs had that set up in stock, at the time. (maybe that's why he pushed the 1405) .... I see they have a 1404 in stock. May give them a call, & enter negotiations. Your input alleviates concerns with present setup, in any event. ... Thanks, again.

[@MyKARSShop]

@@pnwoods thank you!!!

[@scottinWV]

This is a great lesson.

[@MyKARSShop]

Thanks.

[@scottinWV]

@@MyKARSShop I did a similar formula years ago when I used to get some of the car magazines. I knew something wasn't quite right when I'd see a Holley 1050 Dominator on a small block.

[@MyKARSShop]

@@scottinWV it’s such a common mistake to be over carbureted. Sometimes I think guys think carburetor size is a reflection of their manhood. 😂😂

[@scottinWV]

@@MyKARSShop Hmmm. Probably looks bad if I'm running a Rochester DualJet on the lawnmower then.

[@stevecooper8121]

I went and bought a 600cfm vacuum secondary for my 351w. I removed my 750cfm with vacuum secondary. I have a AFR wide band so I can see exactly which direction my tuning is going. After spending 4 hours and 10 different combinations I put the 750 back on and jetted the front and back the same. The 650 out of the box ran so lean it wouldn't idle and to get it to run I had to use jets bigger than what was in the 750.Then it ran richer than the 750 at idle but lean at cruising speed. After some research I found that gas with 10% ethanol is 14.1 roughly for perfect burn and some motors just need more fuel like 13.0 to1.to run good. At idle with 14 to 1 my motor pops and is starved for fuel. I sent the 600cfm back for a refund and deal with the slightly rich 750 with maybe a next size hotter plug and see what that does.I have no gas in my oil so I will probably just leave it alone. The 750 has great throttle response.

[@MyKARSShop]

These ethanol-based fuels definitely throw a monkey wrench in the mix. I’m really puzzled why the 600 wouldn’t work. The idle circuit should work fine. makes me wonder if something was wrong with it Glad you got things sorted out and you’re happy with where you’re at.

[@stevecooper8121]

@@MyKARSShop It was a quick fuel brawler made by holley. The workmanship was terrible, the jets were so over tighten I almost destroyed them taking them out.The thread's were not machine were a crap,the metering plate was a huge fight to remove,the bowl gasket was so smashed that it was torn up. I don't think it was made in the usa.USA. I think your right about the idle circuit being messed up. I have a 30 some year old 600 cfm holly think I will tinker with it.Its way better quality than the new one. I sent it back for a refund. I drive a truck and a fuel hauler told me that they are responsible for the ethanol content mixture. He said they dump in some ethanol and then fill up the tank and don't use any kind of chart. He fills up in Knoxville TN. So you have no way of knowing what your getting 5% ,15% it's all guess work by the driver. NO wonder older vehicles can't run worth a crap on this junk. I think this is more than half my problem using a carburetor. Thanks for replying back have a great weekend.

[@MyKARSShop]

@@stevecooper8121 thanks for filling in the blanks. I appreciate it. I always try to keep track of stuff like this to be able to help people. Awesome. Let me know how it goes with that other 600. I’m really curious. You should not have had any of those kind of issues with a 600 on your motor.

[@borismcfinnigan3430]

@@stevecooper8121 Brawlers are a great carb. You did something wrong

[@cuzz63]

@@borismcfinnigan3430 I have heard of lemons being shipped...got past the QC line.

[@stevenminor2241]

Mike, which carburetor should I use for 1969 Lincoln mark 3...460.engine

[@MyKARSShop]

What’s the maximum rpm you will achieve with the Motor?

[@stevenminor2241]

@@MyKARSShop just street driving little highway 🛣 driving.

[@stevenminor2241]

@@MyKARSShop that's a very good question 🤔

[@megastick9324]

People always seem to equate biggest is bestest. Cams, carbs, exhaust, you name it. Then they “ claim” their combo “ runs fine”. Sure, maybe at some point it does, but , on the street you are 99% of the time over sized on everything. Maybe your car idles good and runs wide open good, maybe not. Maybe it runs great through the midrange but dogs on the bottom or top. My point is, just because it starts and you can do a burnout or run to the gas station and back doesn’t mean it’s running its BEST through the entire range. Most people would be surprised how much better their motor runs through entire range, bottom to top, with LESS carb and cam and a smaller diameter exhaust. Street driven cars are miles away from pure track cars. And , with cars , bikes , whatever, everyone loves to sit around and talk about they have the biggest and baddest, then go on the street and get their @$$ handed to them by a guy with way less size and better parts system matching. THEN they put even bigger stuff on!! Running and running RIGHT are far from the same. People are so surprised at how much less they really need to do what they’re aiming for. I knew a guy that put a 1050 dominator carb on a SBC for the street. It would do burnouts, but he couldn’t drive it anywhere. On the advice of an actual drag race motor builder, He ended up with WAY less cam and a 650 carb and it was a whole different car! But convincing someone they’ve over built is like pulling teeth. This was a good explanation of how much carb you DONT need for a given motor. Making it run, and making it run WELL are two different things, and on the street, biggest and baddest rarely works WELL.

[@MyKARSShop]

Thank you for getting my point of the video. It was actually more about the CFM an engine requires than it was about carburetor sizing. But I was new at KZbin when I did this so I didn’t get how specific and detailed do you have to be with exact information or the nitpickers will tear it apart. lol But the foundation of what I was presenting was about street cars not race cars. And not about what performs on a Dyno. . I ran Dyno cells for years, and I know for a fact that what might perform well on a dynamometer does not necessarily equate to good street performance Thank you so much for watching and getting my point.

[@mdl7534]

Once ive done the math …where would the Cfm be on the carburetor be? Cause all the carbs that I’ve checheck On eBay they don’t come with cfm on the carbs .

[@MyKARSShop]

Holley and Carter carburetors both list the CFM of their carburetors. Other brands, there are listings with specifications that would tell you that.

[@evanmakopoulos8527]

Pontiac 455 should i get 650cfm carb ?

[@MyKARSShop]

600 if it’s a streetcar, 650 if it’s a drag car… But I don’t have enough information to be able to give you a realistic view. 650 if it’s a Really, radical street car… Cam size, torque converter slip … or Stick shift? Application Dash Street car? Drag car… or Somewhere in the middle. All of these things matter so the application makes all the difference. Having said, all of that… 600 to 650 CFM, vacuum secondary for a street car, 650 mechanical for a drag car… You probably will be OK.

[@evanmakopoulos8527]

Wow awesome. So definitely street It has 455 bored 30 over Smog heads Edelbrock performer intake 411 posi rear Currently have holly 850double pumper and not happy. Would like to change the heads to Edelbrock aluminum and change the carb

[@MyKARSShop]

I am revisiting this subject again this coming Tuesday August 22, 2023 I think you’ll find it helpful

[@approachingtarget.4503]

The formula doesnt stay specific to everything. Its a good starting point. If your using separate individual runners, it doesnt work at all. And most carbs dont flow thier advertised numbers.

[@MyKARSShop]

You’re absolutely correct. It’s a baseline.

[@tysonhoover3008]

This is wrong, and you will buy a carb that's too small. The way manufacturers flow and rate carb cfm is at higher vacuum than you will see on an engine. The carb can be much bigger than the minimum required without hurting drivability .. watch dyno videos from motor trend or Richard holdener and you will see this proven.

[@MrBlackbutang]

This didn’t work for my ford 545 Holman Moody heads and 10’000 rpm’s .

[@mstanley623]

I have a 350 sbc with a 671 blower and 7k stall what should I run?

[@MyKARSShop]

This might help www.onallcylinders.com/2017/02/13/how-to-choose-a-carburetor-for-supercharged-engines/

[@deerslayer5863]

Well explained

[@MyKARSShop]

Thanks! Thanks so much for watching. Hope you enjoy the channel

[@craphittingthefan2360]

How do you explain how my 460 ford went from 11.50 to 11.20 in the 1/4 mile just by switching from an 850DP to a Dominator 1050

[@MyKARSShop]

VE.

[@brentsorenson6507]

Now how do those number get affected with towing or hualing etc?

[@MyKARSShop]

They don’t.

[@brentsorenson6507]

@@MyKARSShop would you still tune it the same too?

[@MyKARSShop]

@@brentsorenson6507 I would. If it’s tuned right it’ll perform the same no matter the usage. An engine is simply a pump. If it’s set up right it’ll give you all it has & perform well. Heavy hauling loads are similar to dyno loads. They are very revealing.

[@thewoodsman5261]

I keep doing the math and it keeps telling me I need a carb that is 470 cfm. That seems way to small for a 350 small block Chevy. It's not a built engine, it's a stock 1987 suburban tbi engine that I'm swapping out to a carburetor. The only performance modification's will be an aftermarket dual plane intake manifold and possibly headers. I'm looking at the Holley 90470 but part of me thinks I should purchase the Holley 90670. Any advice would be greatly appreciated. This engine won't see much time over 5500 rpm and it's going in a 77 GMC Sierra K15 4x4.

[@thewoodsman5261]

I wish I knew the cam specs, I've been searching the net high and low and can't find the info on this.

[@thewoodsman5261]

I do know the engine is rated at 200hp and 300 ft lbs at what rpm I'm not sure. On Hollers website the 90470 is recommended for 4cyl, V-6 and inline 6 motors.and I want to put this on my 350 V8 Chevy, am I crazy

[@MyKARSShop]

I’d go with the 670 and then you can dial it on with the vacuum secondary spring. That way the engine is getting exactly what it needs from the carb and you have margin. That’s the beauty of a vacuum secondary. You don’t have to use it all You can dial it in. There’s a video here on that process on my 73 “scoops” swinger

[@thewoodsman5261]

​@@MyKARSShop I apologize for the delay in my response. I appreciate your input and the knowledge you shared. Thank you very much, from Canada

[@mariocastro7814]

Wouldn't carburetor size change the volumetric efficiency too?🤔

[@MyKARSShop]

Volumetric efficiency is a factor of the mechanical ability of the engine to pump and flow air. There’s a video on the channel here about it Thanks for watching

[@deerslayer5863]

On a race car I double cid 355 I'd run 700 cfm street car I run the 3456 method

[@MyKARSShop]

That is an absolutely great rule of thumb. I like it!!!

[@havebenthere]

That formula only works for mild street where you have a broad range your engine may run in. Throw it out the window for anything else! At 100% VE my 355 would churn out a 715 cfm at 7000rpm. I was pulling so much vacuum as the tach rose it was ridiculous. 850 cfm and power was better. Granted I had to tune it for that, but one needs to tune regardless. Lack of tuning skills won't allow you to run an optimal cfm carb. I'm not talking just changing jets and or idle mixture screws. Your myth has been around forever and is completely wrong. It's been proven wrong way back. "the truth you know might not be the real truth"

[@MyKARSShop]

You’re very first sentence says exactly what this video was about Street performance and drivability . This was filmed many years ago when I was just starting in KZbin and was in direct response to a viewer question I have since filmed another one explaining more where this was coming from. But of course nobody is seeing that one. Lol. I never expected this video get any attention at all so it’s been greatly misunderstood Not that I really care. Thanks for watching

[@havebenthere]

@@MyKARSShop I understand. The problem really has to do with the street enthusiast now days thinks 500 hp is mild. The formula which to be fair is promoted by Summit and a whole slew of companies. At 400 hp and less it can still be a problem with undersized carb and running a power valve. The right mix at lower to mid might at upper rpms go very lean due to power valve getting higher vacuum from undersized carb. The real key to picking the correct carb is to really understand carbs and how they work. But everyone wants somebody to reach into their hat and pull out a magic number so they don't have to think. Thanks

[@brandonwoods9866]

Great info. I just subscribed because of this info.

[@MyKARSShop]

Thanks for the sub! That’s awesome. Thank you so much.

[@I_like_turtles_67]

I had no idea Penn from Penn & Teller was so into cars. All joking aside. The information spot on. I'm personally in the process of building a SBF. Working with a recently retired dragster guy. Who's helping me assemble the stroker motor. Waiting to see what he says about how high we plan on spinning the motor. He's definitely more conservative on carb size. So even with 427ci. I'll probably still end up with a 750dp. It's a 67 fastback with a 5spd and 389 gears. So it's gonna be a fun street car.

[@MyKARSShop]

Trust me if I had Penn’s money, my channel would be quite different. Lol Thanks for the great feedback. And thank you so much for watching. Hope you enjoy the channel

[@teemic3019]

iam driving a 355 with an 850 dp on it i started with 600 went to 680vs then 750vs then 850dp each time et time slips improved .

[@keyofg2020]

Does the same equation apply to a four stroke motorcycle engine? How do you determine your volumetric efficiency if you don't know what it is?

[@MyKARSShop]

Yes… The same principles apply. I believe I have another video here discussing volumetric efficiency that you might find helpful. Rule of thumb… Use the number I suggest in the video if it’s a stock engine. 90 or 100% if it’s modified depending on how highly modified it is. Over 100% for anything with forced induction or Nitrous Oxide

[@keyofg2020]

@@MyKARSShop So I have my CFM needs, but the problem is...I don't know what CFM my carb provides. What I have is a 1946 Indian Chief motorcycle. It has longer rods, bigger cam, and bigger valves than normal. Hard as hell to kick over too. My dad says it needs a bigger carb, but he's not exactly an engineer. I have no doubt he's right that a bigger carb is needed, but he's a bigger is always better guy. I'm trying to figure out what the carb I currently have is capable of and go from there to see if I really need more, and then decide if I can modify it or find a more suitable one. Even if you can just point me to some reading material I'd be very grateful. Edit: if it helps the bore of the carb I currently have is 42mm or 1.6in dia.. It works off venturi, I think about .8 ratio if I'm saying that right? Pulls the fuel out of a bowl below.

[@MyKARSShop]

@@keyofg2020 I don’t know exactly what the carburetor is that you’re using but based upon information I found on the web… 42 mm round slide Mikuni flows 118.8cfm approximate! Rule of thumb for carburetor sizing is a smaller carburetor will give you a better bottom end throttle response. The larger carburetor will give you better higher rpm flow. So look at your application and what you intend to use the machine for. If you want a lot of bottom and grunt… A lot of times the smaller carburetor is the better way to go. These numbers may not be helpful, but they should give you some kind of indication of the direction you might want to head for your carburetor. 43 mm round slides Mikuni flows 124.5cfm approximate! 44 mm round slides Mikuni flows Max 130cfm 45 mm round slides Mikuni flows 135.7cfm approximate! 46 mm round slides Mikuni flows 141.4cfm approximate! I’m not overly familiar with the carburetors on an Indian… What make is the carburetor you’re using? Are these numbers helpful?

[@keyofg2020]

@@MyKARSShop I'll have to do some research into the make of the carburetors I have available. I know they are all stamped with a number. One of the ones I have is a linkert M344 I think, but that's all I can remember off the cuff. Ideally, I'd like to figure out how to calculate from the dimensions of the carb if possible, but if not, maybe I could do like you're doing here and gather some data points of various models with the same size and get a decent ballpark, or via linear regression if I can't find the same size. I think this does help me at least by giving me options of how I can figure this out. Thank you!

[@MyKARSShop]

@@keyofg2020 This link might be helpful to you I’m not sure. I wondered if it was a linkert carb www.performanceindian.com/Carbs.html

[@teemic3019]

i have seen a STOCK 305 make its best hp and torque with a 950 cfm on the dyno . Every drag racer out there seen much improved et time slips with a 750 over a 600 at every drag strip around . Just because it is math does not make it right and your made up number of 3456 is wrong ! Ps every body and their bother has a dyno now so !

[@markmixon1121]

Isn’t it weird that Chevy had two four barrel carbs on a 302 ? I don’t think they used this formula.

[@KingJT80]

also a way different engine setup on DZ032s. those were very high compression and mechanical camshafts too so that VE was up there...

[@mikeg4163]

Fuel system engineer? Why wouldn’t you consider booster design and the considerable changes made to modern carburetors? You’re calculations are for 1960’s carburetor technology. By the way, real race engines are well above 100% VE.

[@borismcfinnigan3430]

LOL go away. You wouldn't know a race engine if it fell on you

[@HerrPoopschitz]

Im just glad he broke out the oversimplified antiquated equation within the first few minutes after claiming to be a ‘fuel system engineer’ so I didnt waste my time watching the entire video.

[@markhagan6005]

Awesome video. Great detail. I am new to carbs and have been looking to my buddies for help and they all throw out random numbers. Lol. I am a little stumped on my VE still though. What carb would you use in my setup? 68 mustang driven on the street and cruising. 331 stroker, AFR 185 aluminum heads, performer intake, roughly 6500 max, headers and auto Trans C4 with 1500 stall.

[@MyKARSShop]

Do you plan to drive it mostly on the street? Or is it pretty much a race car that you’re only gonna drive very rarely on the street? If it’s a street car I would use the average VE number that I mentioned in the video In my opinion, and the way I approach it is I want it to be as drivable as possible & not be fouling out plugs and so forth for normal driving. I’m in the middle of filming a new episode on floor pans right now, but I will try to remember to circle back to this tonight and crunch some numbers and offer some suggestions.

[@scottinWV]

Awesome T-shirt!

[@MyKARSShop]

2nd best band ever. 😎😎

[@scottinWV]

@@MyKARSShop I'm guessing AC/DC is your number one then.

[@MyKARSShop]

@@scottinWV nope. My own band. All original & founded in 1982. 😎😎 kzbin.info/www/bejne/gXXLenp_mrFmbJo

[@scottinWV]

@@MyKARSShop Well! I'll be damned! You guys rock!

[@MyKARSShop]

@@scottinWV thanks. 🤟🏼

[@chewybrand238]

How do you take something so simple, and make it so complicated?

[@jtauto74]

My 800cfm edelbrock carburetor is likely to big for my 383 stroker. 3800 Stahl 3 speed.Having idle issues & fuel pooling in intake. I used your calculations & came up with a 650 cfm carburetor. What do you think?

[@MyKARSShop]

Based on experience, especially for a streetcar the 650 would probably perform better for you.

[@jtauto74]

@@MyKARSShop thanks. I'm gonna just sell my motorcycle & purchase, holley sniper efi system. Time for a big upgrade.

[@MyKARSShop]

From everything I hear sniper is a great way to go. I actually hope to put that system on one of my cars eventually.

[@jtauto74]

@@MyKARSShop called jegs & purchasing the efi kit & hyperspark kit Aswell. I'm sick of carbs & the issues. Thanks for your feed back. Great vids

[@MyKARSShop]

@@jtauto74 That’s awesome. Let me know how it goes. I’m really curious and interested

[@frankdepalma4409]

I seen a video on KZbin when a guy took a sound and stock 350 and put it on a Dino. He then tested different cards from 500 cfm two barrel to 1100 cfm four barrels and got the most power with the 1100 ,was this a scam.

[@MyKARSShop]

There would be so many variables in that I would have to see the video to understand exactly what they were doing. Remember that everything I’m talking about here is for a street car not a race car. When it comes to race cars, all of this goes out the window. I doubt it was a scam, but I would be curious to know the exact set up, the exact carburetor, vacuum secondary? Mechanical secondaries? What kind of loads were they putting on it… Also what did the plugs look like after several hours of driving and running… Etc. An engine is an air pump… They can only move so many cubic feet of air based upon its displacement and mechanical configuration. If you happen to find the link, I would love to see the video and look at what they’re doing. Hey thanks for the awesome feedback. I appreciate it

[@soobok13]

Hi I have a 383 stroker engine but it is unknown. I have no specs and don't want to tear it apart. What carburetor would you run I have a 2800 stall converter in my 700r4.

[@soobok13]

I want the best bang for my buck carburetor any information is appreciated.

[@MyKARSShop]

If it’s a street driven car, I would go with either 650 or 750 vacuum secondary. Then you can tune it in the way you want it. Myself I probably would go with the smaller 650. On Streetcars I like some good bang for my buck, but I’m not looking to milk out every ounce of performance. I also want to good drivability.

[@soobok13]

@@MyKARSShop Hi, thanks for the suggestion!

[@JohnRocks6368]

@@soobok13 your comment is from a year ago so any input I have is probably too late :) I would run at least a 750cfm. That is what I have on my 383 stroked SBC. 3000 stahl and turbo 350 trans with 4.10 gears in 68 Camaro. A street and occasional strip car that has run 11.62 in the quarter mile. I would also guess if I got my hands on a 800cfm it might pick up a little time. Hopefully your engine combo has been worked out

[@dce428]

The math says. a. FE. 390. At 6k. .85. ÷ 3456. Wants. 575. Cfm. ? Do why does a FE. 390. Make more power with a 750 dp. 25 ft tq. Over a 650. Carb. On the Dyno. The Dyno don't lie. Something is not right with the formula

[@MyKARSShop]

The formula is designed to give you the most driveable carburetor for a street car. Not maximum horsepower. It may make more power with a bigger carb on a Dyno , but if you put that big carb on the street you will likely feel throttle response go away and your low-speed power drop off. The formula is designed to give you the best carburetor for overall street performance Thanks for watching .

[@dce428]

@@MyKARSShop 25. Ft tq. As low as 2500. Rpm. Increase. Going from a 650. To a 750. DP. Seen a 416. 390. Stroker with just a 233. .050. Pull 716. Cfm on the meter. Being dynode at only 5400. Rpm. OEM iron heads. So the formula. Is way off. Now if it's 100%. Bone stock. Single exhaust. Then mabe it has some merit thank you for your time sir

[@Truther00]

Nice intro song Mike 👍🏼

[@MyKARSShop]

Cool. Glad you enjoyed it. Thanks for watching.

[@jeromejakubowski7763]

Thank you for putting this exce video on this subject I know of guys that have made this video mistake. Your videos definitely rock 🤟🏻

[@MyKARSShop]

Thanks!! Glad you’re enjoying the channel. RAWK on!!

[@jeromejakubowski7763]

Thank you for the response darn I just realized I misspelled a few words, I apologize and I’m a little embarrassed.

[@MyKARSShop]

@@jeromejakubowski7763 i’m constantly making typos. No big deal at all. It’s social media, we all do it. I appreciate the feedback and appreciate you being here.

[@jeromejakubowski7763]

@@MyKARSShop thank you again yes I definitely enjoy your channel and everything about it, your intro is really awesome. I think it sets the right vibe for your channel. I really enjoy being subscribed to your channel and thank you for taking the time and effort to put this out.

[@MyKARSShop]

@@jeromejakubowski7763 thank you for that. I really appreciate knowing that. The early stages of growing a KZbin channel is very frustrating, and your feedback is encouraging. I have so much stuff I want to do, sometimes three episodes a week doesn’t feel like enough. But I do have a life and businesses to run. Lol lots of cool stuff coming though. Thanks for being here

[@thedobermangang3503]

very good video my brother

[@MyKARSShop]

Thanks for the visit. I try to put out both educational and thought-provoking Contant even if it’s unintentionally wrong, Lol If it gets people thinking, and researching I feel like I have succeeded. Thank you so much for watching, and commenting… I hope you enjoy the channel. 🤟🏼🤟🏼

[@1crazypj]

Isn't VE on a stock 60's muscle car closer to 65%? (it would have to be in view of the low power outputs compared to engine size) About 20 years ago, I remember asking VE on Pontiac 400 motor and 'Pontiac Owners Group' were 'convinced' VE was 100% 🙄 At least I now know why 3456, doesn't it matter how many cylinders are drawing through carb though? Street motors running 8,000 rpm are out there, but (big BUT) most of the time they are only turning 3¬4,000 or less Ram air is pretty negligible below 400mph compared to what the engine is already drawing in (for anyone else's benefit as you already know that) BTW, I almost exclusively work on motorcycles, Suzuki were getting 130% VE at 150mph but that was a modern design optimised for airflow

[@MyKARSShop]

Great feedback. I’m not sure on those VE numbers. I’ve been going to do a more in-depth episode on VE but I haven’t gotten around to it yet. Thanks so much for watching. Really appreciated your comments.

[@1crazypj]

@@MyKARSShop True story, Back in the late 80's, Kawasaki were developing a ram air system to get more power from the 600cc motor. LEDAR Race developments were doing the work . The owner was a bit of a maverick and didn't particularly like big corporations (but obviously liked how much they would pay) so, He developed Kawasaki Fresh Air Ram Technology Systems. The Japanese engineers didn't see any problem even when marketing reduced it to an anagram but, when it got to USA, they burst out laughing because 'Kawasaki FARTS' I only got to speak to the guy a few times as he developed carb kits for motorcycles, unfortunately he was killed in a hang glider accident in early 90's (and I can't remember his name which kinda bothers me) I was working for Suzuki when the GSX1300F was developed, they actually measured the 130% and had to develop some new software to richen mixture in 5th gear but due to a 'Gentleman's Agreement' limited power in top gear for a max of 300Km/Hr (about 187mph)

[@MyKARSShop]

I love stories like that… how funny. FARTS! Lol. Hopefully, you remember the dudes name. I worked for orbital engine company as a dynamometer technician in the early 90s…. And then went on to work briefly at Mercury marine, implementing the orbital technology for the OptiMaxx engines. So much amazing stuff I got to experience back in those days. Love your comments. Thanks for taking the time.

[@1crazypj]

@@MyKARSShop Leon Moss, came to me out of the blue while I was reading your comment.

[@MyKARSShop]

@@1crazypj that’s cool. That name rings a bell. I’ll have to look him up.

[@DuddiesAdventure]

Great Video! This will help not drown out all the potiential Armadillos your motor can make! I might need to run the numbers on a few of my vehicles hahaha Great Job Mike!

[@MyKARSShop]

Drowning armadillos can be very problematic. Thanks Duddie.

[@markparker5788]

Drowning armadillos doesn't sound like good decision making.

[@MyKARSShop]

@@markparker5788 lol

[@dallencloyd1776]

These formulas make sense on paper, but then you think about real world applications like the 302 z/28 had 2 780cfm carburetors and performed extremely well. The 340 six pack had the same carburetors as the 440 six pack and both performed extremely well. Maybe someone can shed some light on this.

[@MyKARSShop]

Two things… First of all factory high-performance engines had a higher VE number and not use the number that I am using here. Secondly, most of these engines, and I admit not all, but most used vacuum secondary carburetors that did not nearly fully utilize the secondaries. Especially engines that utilize thermal quad, Quadra jet, etc.… Secondary air doors were strictly controlled by the amount of air the engine was demanding. Remember in a production environment, you’re trying to find a “one-size-fits-all “carburetor that will work across multiple applications for cost… The more you buy the cheaper they are. Hence the vacuum control secondary carburetors were great because an engine won’t take more than it needs. Thanks for your question. I’m sure there are people that know a whole lot more about this than I do, but this video was intended to be an introduction to get people thinking. Thanks for watching

[@cuzz63]

@@MyKARSShop cant speak for all those carbs but not all CFM's are equal across the board. Also some of them used spread bore carbs which does allow for a larger carb since your mostly driving on the primaries.

[@MyKARSShop]

@@cuzz63 I probably will do another video on this because I focused too much on the carburetor here when, actually, the point of this video was engine CFM. You’re absolutely right that advertise CFM on a carburetor versus actual CFM is not the same thing. Hindsight being what it is… Lol. Thanks for the great feedback.

[@doomman700]

Regardless of the math, if you see big vacuum under the carb, it will not function as well as a carb big enough to have low manifold vacuum under it , as it will mix better. Every pro stock out there used dual quads for a reason. It’s also why my Pontiac has 2x4’s on it mixing the air fuel better in all 8

[@Abihef]

This is a great great video Shame I'm from and in a metric country😂 But awesome video, gonna have some conversion to do in a bit. Best part is I'm only building a 85cc 12-14K rpm engine right now😂 Aimed at 4500-9000 in use regularly but I was just thinking about how little suction the engine could create in a carb with a venturi bigger than the manifold. Hope I can translate this well to my case got a 20mm stock at 50cc now, percentage wise from 50cc to 85cc 26mm would roughly be the same ratio but with only a 19,5mm manifold that seemed like a bad idea. When tuning two strokes I used to get crazy performance on small racing bikes with 14mm on 62,5cc though. 13,5 honed intake manifold that was, (12 stock I believe with a 9/12 at 50cc) Anyway, great video to help me on the way. And gonna be a shame when this project is done, gonna need me something new to build.😢😂 But for now a whole lot of calculating, flowing and tuning to do.

[@Abihef]

Yeah it's a long read but I just love engines and get carried away. Can't wait till I've got a place big enough to get some cars in to take apart

[@MyKARSShop]

I had a similar discussion somewhere else here in the comments about smaller engines. I can’t remember who it was… But dig through the comments and you might find some more helpful information.

[@MyKARSShop]

Thank you so much for watching. I really appreciate it. I’m glad you found it helpful

[@Abihef]

Awesome, thanx indeed and it sure was. In the end I found a specific simplified formula that works great and seems fairly similar. Immediately turned it into a program in my calculator from high school (ti-84 plus) for future projects. Turns out I have the right carb for the engines target rpm, 20mm at 7500 for 85cc and need 26mm for my target rpm of 11000 so I'll break the build in at twenty and go from there. The formula was; Diameter = efficiency [eg 0.85] * square root of (volume in liters * rpm) In my case that is 0.85*sqr(0,085*7750) which comes to roughly 19,5 which is exactly my manifold and carb that I've bought which I thought was proper. With my new cam and cdi though it comes to between 24 and 26 but since the heads inlet is only 20 I might keep it there. Great kick-start you gave me though

[@clipvue222]

So with a smaller carberator would the vehicle get better gas mileage

[@MyKARSShop]

It would get better gas mileage if it’s not over fueling… And of course when you stop your foot into it with a smaller carburetor that will also make a difference. I have always found smaller carburetors to be more efficient & provide better drivability and good performance for a streetcar. If it’s a race car? Put on a toilet bowl. Lol. 😂😂

[@cuzz63]

Thats a 10% difference in CFM, when you went from the 85% to 95%...thats more than not much.

[@arlenewolf5260]

Why does the math basically call for a Holly 600 on a mild 350, yet the factory Q-Jet from Chevrolet is a 750?

[@MyKARSShop]

Quadra jets - by design - only flow what engine the will take. A 350 doesnt get a q jet to open up all the way. Factory used this type of carb across multiple engine platforms for cost reasons.

[@arlenewolf5260]

@@MyKARSShop Doesn't make sense to me, WOT is WOT

[@MyKARSShop]

@@arlenewolf5260 on a QJ the throttle blades might be wide-open … however The secondary air doors are not. They limit/control air flow so that the engine can take the air & fuel that it needs. That is the brilliance of the Quadra jet design. And why they were able to put such “large” carburetors on so many different engines. They did this because they could use one carburetor across multiple platforms, and the carburetor would literally become what that engine needed for CFM. Especially in thermo quad and Quadra jet world… Rated CFM… Does not mean that the engine utilized all of that CFM.

[@stevecooper8121]

So I'm very confused about the formula behind determining the size. This say you have a 351windsor. 351 cubic inches and say it goes to 6,000 rpm which I think is at least 500 to 1000 more than a stock engine will take.Now we take the value at 85% which again is at a very high end for a stock engine.Now after ÷ this by 3456 we come up with 518 cfm. So my stock 1987 F150 came with a holly 600cfm carburetor. When I use 351 cubic inches and 5500 rpm 80% value this goes down to 447cfm. With that being said, why would Ford use such a big carburetor that would cost more ? I think the Ford engineering department had figured out exactly what the engine required. That's why I think this mathematical formula is misleading at best. I'm not trying to start some war with you, I watch your channel and really enjoy your video's. On another subject I'm going back to the drag strip tonight with new micky Thompson 295 ss drag radials to try and get into the 14 second bracket. Stay cool and keep making videos, really enjoy your shows.

[@MyKARSShop]

Common question and I appreciate you asking. Factory used common carburetors on multiple platforms for cost reasons, but they didn’t necessarily utilize that carburetor 100%. The secondaries were tuned to match the engines needs. That’s the beauty of a vacuum secondary carburetor. . 100% flow on the primaries and 50% flow on the secondaries would get you about 450 CFM

[@MyKARSShop]

Let me know how it goes at the strip. Curious to hear how it goes. keep rockin.

[@misters2837]

As M.K.S. (those are actually my Initials LOL) stated, it cost the manufacturer a lot of money to certify ONE carburetor for emissions purposes and therefore you would see that carburetor on 351s and or 302's and maybe even California 460's they didn't want to spend tons of money on something that was likely only going to be certified for ONE YEAR!

[@cuzz63]

the bigger carb doesnt cost anymore than a smaller one..more likely they used an off the shelf carb that was close..

[@johnmerklinger4566]

Holley tech told me 650 mechanical secondaries for a 355 vortec, (EQ ch350 heads), RPM to 5,500, mud bog jeep motor. According to your math I’m way over carbed. Any opinion on this? Thanks jack.

[@MyKARSShop]

Use a higher volume efficiency and you’re probably about right The number I’m using here is for a basically stock engine

[@johnmerklinger4566]

@@MyKARSShop thank you very much. Appreciate your opinion

[@biggene1711]

So 427 with a 780cfm red line 6000 ? 550hp ???? I 🤔 do I need a 850cfm ? Hell I don't know...

[@MyKARSShop]

Thanks for watching I elaborated on this more to clarify where I was coming from in a recent video. kzbin.info/www/bejne/oIHQmKWol76kqrMsi=jrtL7g34g169QhQf

[@MrEntede]

This is incredibly inaccurate to what CFM my engine ran quickest with. 15.5:1 alcohol 310”sbf shifting at 8800 with a liberty style five speed. Based on your calculation it would run best with a 750. The 750 4500 went drastically slower than the 1050 4500 which went marginally slower than the 1140 4500 on the same track with the same AFR as well as nitrous jetting and bottle pressure.

[@MyKARSShop]

I wasn’t clear in the video that I wasn’t speaking about drag racing… was talking more about Street performance I also didn’t bring alternative fuels into the equation. It’s hard to cover everything in a short video. Thanks for your great feedback

[@MrEntede]

We all like to bounce ideas and results off of each other to get better at what we do. Thanks for making the video! It’s a great way to start the carb tuning journey.

[@MyKARSShop]

@@MrEntede thanks! You’re right. We all learn from each other. Thank you for watching, and thanks for the great feedback.

[@ferdinandcuevas8457]

Great content Thank You . 🇺🇲🇵🇷🦊👍

[@MyKARSShop]

Thank you so much for watching. Hope you enjoy the channel

[@craigdoucette-xo2mp]

Maths wrong…. Cubic Inches x RPM / 3456 = CFM (cubic feet per minute) / Volumetric Efficiency First calculate the CFM. CI x Engine RPM/ 3456. That will give you the CFM. Then divide by the volumetric efficiency, that will give you the carb size you should shoot for.

[@bigbelconut]

Your figures were developed by carb manufacturers because of people over caring and returning cards. The dyno tells it all , so according to you my 505 should take a 970. My engine made 22 more hp going from a 1050 to an 1150 carb. What about dual cards on factory cards, or 3 duces . I think engine masters did a show on this and your info was totally wrong. That dry erase board doest run down the road. Totally stock 350 has a 750 cfm carb. 340 Chrysler with a 1000 cfm thermo quad. Under carbing is worse then over carbing.

[@MyKARSShop]

I ran Dyno for many years and I will tell you that… What works on the Dyno for maximum performance doesn’t necessarily perform well on the street when you’re driving the car to get groceries or go to the bank to make a deposit. Thanks for watching

[@Texasmule]

Thanks...I'll just stick to my 650

[@BadTreeProductions]

Two words, Thermoquad. No math needed. 😉😜 Thanks for sharing Mike, excellent explanation for all us cavemen.

[@MyKARSShop]

Very true, thermo quads and Quadra jets are both FOD carburetors. (Fuel on demand). By the way that’s my term. 😂😂. Similar to but not exactly the same as a vacuum secondary Holley

[@jeromejakubowski7763]

So awesome to see you guys follow this channel as well 👍🏻👍🏻🤟🏻

[@angelfigueroa310]

You’re wrong. Bigger is better After installing a 750 double pumper on my lawnmower I am able to shave off .2 sexy off the time it takes me to cut my lawn .

[@MyKARSShop]

I literally laughed out loud. You’re my kind of people with my kind of sense of humor Thank you so much for watching. And thanks for the good laugh Now excuse me while I go bolt my 671 blower on my Stihl chainsaw with a pair of 750 Holley double pumper’s 😉

[@kepjames333]

😎😎😎😎😎😎😎😎😎😎😎😎😎😎

[@apachebill]

Soooo…. No Dominator and 2” headers on my 305? 😂

[@MyKARSShop]

😂😂😂😂 Thanks for watching

[@charlesramirez928]

When it comes to carbs...yes it does you can easily over carb..and your motor will burn more fuel foul more plugs and make no power...fact...

[@MyKARSShop]

Efficiency is everything. Thanks for watching. Hope you enjoy the channel

[@charlesramirez928]

@@MyKARSShop I did thank you...