Dynamic Compression: Biggest Engine Building Mistake

[@kylerrichardson4858]

6 years later and this video just kept me from changing my pistons. Thanks, bud.

[@robertwest3093]

I remember those old vintage Holley and M/T valve covers. Every other hot rodder in the 80s had a set. Now they are sought after.

[@stvkomer]

Biggest bang for the buck was re-timing my stock cam on my smogger 460. Runs top notch 👍 don't want to lose my low end torque so kept the factory intake and cam. Only changed the cam timing and ignition curve. Its like a different car now for about $100 and a evening of tinkering with it. 😎

[@brantkinnsch]

Ford retarded them 4 degrees from the factory for smog

[@imaouima]

@@brantkinnsch Just 460s or were all their V8's retarded in the "smog era?"

[@brantkinnsch]

That is a good question off the top of my head did not know of any others but it would not surprise me, My buddy advanced his cam four on his f250 and got like 60 hp and picked up 6 mpg. I would say if you can find your stock cam info go on wallace racings DCR calculator and play with the numbers. Ideally you would want to be just under 8 for a iron headed pump gas deal. @@imaouima

[@Moparmaga-1]

I'm glad you pointed out the overlap, intake open & exhaust closing are very important. Very very important. I had a 7.8:1cr 1973 400 BBM factory rated 225 hp in a charger back in the days. Not sure the cam timing events but I put a mopar purple shaft 280-474 @ 110 lsa in it & boy oh boy it was all the difference it needed. Before i understood compression ratios I thought hmm if you get more air and fuel in the same area its got to affect the compression ratio somehow. It was a nasty sounding cam, it wasn't huge & even ran on the stock converter.

[@williammorton9176]

she doesnt do to bad on traction she works pretty well still trying to iron her out some but thanks man its been alot of work!

[@robplotts9412]

Stay around 10:1 and ya wont have a problem running pump gas. Most people think more is better but its just not true. If ya really want more grunt work with your rear gear ratios. Lets face it most daily drivers dont get to go much above 100 mph so if ya build it to hall ass 0-60or 70 ya dont need all that cam lope and hp all be it sounds fantastic ya dont need it.

[@Mcleod0000]

I have 10.2 to 1 compression with I think it was below 8.5 dynamic compression maybe it was like 8.4 . I run 91 and 34 degrees advance timing . 66 abdc intake closing point its the 280H magnum cam . I cant get the idle under like 900 rpm . Im all about big engine that you can idle slow . Im not a fan of pumping unburnt fuel out the exhaust on a street car if I can help it

[@jessesyfie7244]

I'm doing a 350 chevy, 9.8 static and 8.4 dynamic, u think it will run without pinging on 91 octane gas with a little timing?

[@Mcleod0000]

I actually think that cylinder head design has much more to do with how well the engine handles compression . I saw a chart that shows that engine temp has a massive effect on preignition . I run an oil cooler and a massive 4 core radiator , I swear I have 10-1 compression + and never even heard the thing backfire . the car isnt a daily driver , so i havent been driving it . but i ran the cheap gas and got it up to temp and it seems great . I think you keep it cool , and try not to lets say climb hills when its really hot at a low rpm , and my guess is youll proabably be fine@@jessesyfie7244

[@richardvanmarter8780]

Good information, LSA makes a big differance in dynamic compression, tighter raises it wider lowers it, tighter more overlap, wider less overlap

[@blakefelice6625]

Wait. More overlap reduces compression. Because you’re “blowing” air out of the exhaust valve because it’s still open.

[@smokeygasser4037]

You can run 12:1 static compressor on pump gas with overlap and bleed off but it's all about combustion chamber shape and compression squash with no sharp edges on dome or head chamber it works great 👍 for my engines

[@ThunderHead289]

The word your look for is squish and it relates to quench. Bad quench causes detonation - ideal quench is roughly .042 between the piston top and the bottom of the cylinder head. From there, dynamic comes into play since it’s the real compression with the cam overlap factored in

[@littlevman2997]

Ideally. 042 is the max. .027 min is possible with low piston rock and the closer the better with proper build. After .040 detention potential increases greatly. If you can keep tbe piston under .040" throughout dwell as the piston is moving back down detenation practically a non issue

[@jessesyfie7244]

I try and shoot for 8 to 8.5 dynamic on my engines depending the cubic inch size. I think a bigger bore longer stroke u want a little less dynamic number, smaller bore shorter stroke u want more . I just did a 350 chevy with iron heads 8.45 dynamic, runs good on 91 octane. No pinging even at 12 degrees intial timing and 36 total.

[@groomlake51]

I preach dynamic compression all the time. It’s so over looked. Most cams actually help not hurt compression. Volumetric Efficiency period effects dynamic compression. Any time you help a engine breath you gain VE wile raising dynamic compression. If you multiply your static compression by the VE number you get dynamic compression.

[@jessesyfie7244]

How do u know your VE number on an engine to do that math?

[@catsontheflatsfishing6023]

Where do I get a single carb tunnel ram like you have, I’ve looked everywhere and haven’t found one

[@williammorton9176]

493 ci and i run 93 octane locked in at 34 degrees total timing all in at 1800rpm it runs like a champ no issues yet and i just got done making about a 180mile round trip in her

[@ThunderHead289]

+William Morton no wonder the thing rips. im sure she can really lay it down. #prayingnfortraction!

[@groomlake51]

Dynamic compression is real world and most important. I has more to do with cylinder head VE. You can run hight static numbers with oem stock heads because the VE is down and the head doesn’t flow much. After market high flowing heads have a lot higher VE so your dynamic numbers will be much closer to static witch is based of 100% VE. The LS platform is around 80% VE. So you can do your math from there. Pro Stock drag engines will get up to 130% VE meaning the engine consumers 30% air and fuel them it’s static volume. Choppy loping cams the every one loves really is the engine running like crap at low rpm. A big over lap uses the exhaust gas velocity energy to scavenge the fuel air mix past the intake valve moving off the seat. It works best with a tunnel ram type intake with long runners. If you can get line of sight down the carb and see the intake valve. That column of fuel and air with create positive pressure @ tge back of the intake valve. It’s a natural super charging effect. It’s crazy not to see tunnel rams much any more. It’s the most bang for your buck on most v8’s.

[@edwardcold7431]

Im building a nice 408 afr head single plane can i run 9 to 1 dynamic on 91 with a water meth spray up top were i will build cylinder pressure with my hot cam its wi d e and 108 lobe sep

[@jessesyfie7244]

I'm doing a 350 chevy with 8.4 dynamic with my camshaft, u think it's going work on 91 octane gas?

[@joe-hp4nk]

What is the engine used for is the most important question. If it's a race engine with heads that flow like no tomorrow. Then you need to match it with a big cam and high compression ratio to keep up the cylinder pressure ie 200 psi. A street engine only needs 160 - 180 psi and you can get that with 9:1 ratio and a rv cam. You can run a bigger cam but you need good heads or it's a waste of time and money. It's a balancing act.

[@ThunderHead289]

These heads are a 54cc chamber with a 2.02 intake valve, unshrouded.

[@joe-hp4nk]

@@ThunderHead289 I'm not sure what you have for pistons, but based stock bore and stroke and flat tops with 4 valve reliefs and a .040 piston to deck clearance which includes the gasket. You should have about 9.6:1 compression ratio. Back in the day when pump gas was 95 - 105 octane, factory muscle cars were 10.5 - 11.5 compression ratio, and the cam had durations above 300, they ran like scalded dogs. Now days with pea coming out of the pump, it's more of a balancing act between cylinder pressure and detonation, I would cater more to lift than duration for that reason. But then you have to up grade the valve train, there's always a trade off.

[@Palmerjct]

My cam card says 39 degrees ABDC @ 0.050”. Is that the number I use cause that doesn’t seem right. It’s a BTR stage 3 truck cam for an LS2. Everyone else seems to be around 60-70.

[@rong4189]

Thanks ThunderHead289, great vid. Would you say that a 'cranking pressure' calc is also an important factor in planning/choosing a CR for a street engine? I ask because I heard that 165psi is about the limit with 91 octane (Calif. gas) but can't find much info on this. Thanks again!

[@obsessedwithcars219]

My prelude has 200 psi with 91 gas and no knocking

[@jesseduke694]

Whats the link? I want to use a dynamic calculator. Ive found a couple that I've used & they are not all the same. I wanted to see what you recommend. For static compression ive found diamond compression calculator to be the best i know of. But I am currently building a 390 & am paying very close attention to quench, compression, & dynamic compression.

[@atvdave88]

All my numbers put into a calculator and its saying i should have 10.35:1 with 8.61.1 dcr i did a pressure test on my cylinders and its pumping 225 psi per cylinder 😮383 stroker.not sure if it will run on 93

[@ThunderHead289]

Man, hard to say - but I'll tell you this, you are going to love that engine if you can get the octane to behave

[@Stainlessslayer]

good video. There are also calculators available if you know all your specs. SW Iowa by chance?

[@vermontvermont9292]

Next, I need to research why some have 93, and others only 91. Here in VT we have 93 everywhere. Also many sell non ethanol 91.

[@williamarnett9064]

Dynamic compression is the only good way to build any engine. It allows you to focus on the cylinder pressure which separates the boys from the men

[@williammorton9176]

man you really know your shit your videos are allways great

[@ThunderHead289]

+William Morton thanks man, i really appreciate the input! this dynamic compression thing is a big deal that many never consider

[@robertsylvester5518]

+ThunderHead289 please check my question above this one.

[@robertsylvester5518]

+Robert Sylvester the calc I'm using has me add 15* to the ivc I'm guessing because it's rated at .50" but I'm not sure if the cam card is at .50"

[@robertsylvester5518]

+ThunderHead289 everyone I try talking to has no idea what I'm talking about and it's getting VERY frustrating

[@ThunderHead289]

id call in to get all the logistics straight on the cam card. measure twice cut once mentality here.

[@bungcheese5901]

I wonder if you'll reply, what dcr would you recommend for 93? That's commonly available to me at the pump

[@bungcheese5901]

On that note, do you think a high dcr would benefit from water/methanol 😈😈

[@ThunderHead289]

Heck anything benefits from water meth - the Hangup wth that is that methanol corrodes out Aluminum parts. A lot factors into what you can handle with dynamic - if you have Aluminum heads, good quench, and chamber design, then 8.5 is really the highest dynamic ratio you want on the pump. (Sounds low, but don’t interpret it the same way as static)

[@markrich3271]

Why didnt you can advance your cam to change power band down low to suit the truck better .

[@ThunderHead289]

If a vehicle that is daily driven needs something different than what it has, I'd much rather switch cams then bandaid the situation. I feel you though, had this engine not be destined for the galaxie again, I would have changed it. The f100 was just borrowing it for a year.

[@markrich3271]

ThunderHead289 I understand there is a proper camshaft for the motor . Rather than spinning the motor higher to get the tq you need with a truck . I personally would rather but the right cam but if you just dont want to cant or will be swapping the motor soon advancing the camshaft a few degrees is better than nothing.

[@ThunderHead289]

agreed, i just didnt want to pull it apart since i took it out of a car it was right for, and it was going RIGHT BACK in that same car. didnt seem worthwhile to me to have to do the job twice, versus being tempted to light to light the truck a bit. the f100 has a mustang 5 speed and 4.11 gears, so it handled it just fine. it just lost its towing ability for the year. was by no means, not derivable.

[@naveedaka]

how about 7.28dcr...is it too less??

[@robertsylvester5518]

Hey thunderhead, I'm building up a Mopar 440 to a 507 with a .528 purple shaft cam and I'm looking to go to a 7.9 dynamic with the cam advanced 3* for seating to happen at (ivc) 69* but that makes my compression 12.2:1 will this run on pump gas? I'll go on your word

[@ThunderHead289]

+Robert Sylvester as long as your dynamic compression is less than 8.5, you can run pump gas. after that with dynamic, you will lose way to much power from having to jet rich and pull timing.

[@robertsylvester5518]

+ThunderHead289 according to the calc I used before I would need 12.2. according to the calc in the link I need 10.3. the calc in the link requestes more info so I trust it more than the other. the other has you add 15 degrees to the ivc. im guessing to compensate for @050? or measured at .005?? not sure but let me know what you think. thanks for the quick reply!! www.uempistons.com/index.php?main_page=calculators&type=comp&zenid=5d236f45833044eb782d2eb69bc64b8e

[@ThunderHead289]

i will look into this and get back to you. dont want to steer you in the wrong direction.

[@robertsylvester5518]

thanks!!

[@robertsylvester5518]

+ThunderHead289 any luck??????

[@dangerousfreedom4965]

Great page, thank you

[@pedrosilvaslva2625]

How do i mesure dynamic compression?

[@RobertKohut]

Nice info, thanks!

[@gyffjogofl7676]

Eye opening. Thank you!

[@williammorton9176]

9.19:1 with an effective stroke of 3.58 interesting

[@ThunderHead289]

+William Morton dang, what size engine do you have? and if thats your dynamic, im sure it rips, but i hope your on race gas!

[@53_ford_custom15]

do a video on flatheads please

[@crazyc99]

Golden key

[@rogerstill719]

The more overlap an engine has, the more cylinder pressure it will have.

[@ThunderHead289]

Opposite actually when compared to all things equal the same engine with less overlap in the cam

[@jessesyfie7244]

Im thinking this is actually true.

[@kevinwest3689]

Don't hate on people that have 12.1 and a 383. There's a chance you're not the end.be all. Grand wizard. I truck Doesn't run better, because it has a smaller cam. My truck has 10.7 a stage 2 cam on 91. It comes in low Is peck torque at 4500. 100 hp over stock rev to 6500. It's a #truck cam.

[@ThunderHead289]

Man, this has to be from like 10 years ago

[@kevinwest3689]

@@ThunderHead289 And yet, it's still posted. Admitting when you're wrong about something isn't really an iowa thing. So...carry on👍

[@ThunderHead289]

@kevinwest3689 I don't remember what I say in the video, but judging from the title I was probably talking about how a lot of folks stuff in too big of a cam for their engines static compression. A big overlap cam is totally fine when the engine is built correctly for it - unfortunately many people just don't. And I feel that - I think most people un general today can't admit when they are wrong. Try working in engineering - basically the poster child profession of that IMO

[@timothyleonard5540]

So even with aluminum heads 8.5:1 is the magic number

[@ThunderHead289]

Indeed it is - can probably fudge it a bit higher for dynamic compression with aluminum heads, but also aluminum heads decintigrate with preignition

[@timothyleonard5540]

@@ThunderHead289 well I'm looking a doing a 347 with twisted wedge 11r 56cc chamber and ford's z303 exhaust closes 3 deg intake 41

[@dynodon427]

Thank you for sharing!

[@ThunderHead289]

No problem, literally how I get power out of so many peoples rides that complain of issues.

[@williammorton9176]

im checking mine now just because im curious

[@stephenhans189]

Girl in highschool was named thunderhead too .

[@ThunderHead289]

I named this channel after your mom

[@stephenhans189]

@@ThunderHead289 You knew her well then.

[@FIVE-0-APOCALYPTO]

yeah exactly basically. hey I'm going to get a big cam without all the other parameters to utilize it properly.... hi I'm an idiot! back in the day when you had to do things by hand and you either had to know what you're doing because somebody else gave you the parameters or you just simply had to take a chance because it was very common that somebody go through a lot of trouble and build up some big block monstrosity but all the parameters are not matched properly and then some little 351 Windsor with milder components but yet everything is matched perfectly beats that big block monstrosity. A engineer told me back in the day because he had it figured out basically at sea level conditions and i describe to him the typical drag race out on the street that took place back then in the 80s. The typical race was you already at first gear because there's some other guy in the other lane behind you going down the main street of your town and he knows that you got a ride and you know that he has a ride and sure enough he starts coming up on you and gets next to you and you know it's on it's just a matter of who's going to gas it first because before you gas it you got to look around and make sure it's not a cop and that there's not another car that's coming out of an alley or whatever and that usually takes less than 2 seconds and since I'm already in low now he puts it in low and you're doing about 3500 RPM and I will admit I was usually the one that stomped it first because I typically had the most guts cuz I didn't care about a ticket so what you have here is a mid-range the top end race and that's was drag racing on the street and for every 20 races I had like that I still can't remember one from a dead stop. He heard my explanation of a modern-day drag race and he looked at me and said go get yourself an LS6 crate engine long block and put a 3/4 lift cam in it with a Victor Jr intake and a holly 650 CFM carburetor. I said, you mean like a double pumper or something? And he looks at me and repeats line 1 again: order yourself an LS6 crate motor, put a 3/4 lift cam in it etc etc I said, okay okay what about exhaust? headers? (shrug) If you want to. Are you sure that's a big enough carburetor for that engine what about gear ratio and so forth. He looks at me and repeats line one again with that look on his face that I'm a dumb 25-year-old and I just don't get it.... and of course he was right. Because he explains me that I told him what a typical drag race is and therefore as he said if you do what I said he said you will blow the doors off of everything on the street. looking back on that now I know that he was right even though I was just some idiot thinking well if it doesn't have a big Cam and all that shit..... it was just me who didn't know shit. And I mean doesn't it totally figure that this guy approaching his sixties and a mechanical engineer and fiddling around with cars like he had a Jaguar but with a 350 Chevy engine in it but the body was from Germany where it was like zinc plated or something where there's no way it could ever rust I should have bought that car now that I think about it and he had a son beam tiger parked out on the street because it wasn't exactly known that maybe the car is worth a million dollars now but it's not like he got screwed and sold it to some young whippersnapper for next to nothing he knew what he had and he didn't want to sell it and he wasn't getting rid of it and he didn't care that it was sitting there out there in the street because it needed restoration anyway but it ran there is nothing wrong with it other than faded paint and the card probably needed to be taken apart and restored because let's face it it's a Sunbeam Tiger and totally worth going through. But the classic thing about this story is the other vehicle that he had that I never heard and I never seen it run but it was one of those 70 or 71 ranchero Fords with a 428 or 429 and I can't remember and just a total sleeper but he didn't build it with the intention of it being a sleeper but listen to the other cars I described he's just one of those kind of engineer guys that as he said no Paul if you get your setup that I said you should get and you'll blow the doors off of everybody you're not going to blow the doors off of that ranchero and one day I'll start it up for you but I never got around to seeing him very much and to this day it's a mystery how well that car went but I'm sure went real good because believe it or not up until about 1993 and being around a lot of cars and so forth, the most badass car I was ever in was a 67 GTO with a 383 in it four-speed and that six pack carburetor whatever the hell they called it and it was all stock and sometimes a guy would give me a ride to school in the few times he did coming out of the neighborhood I always told him to stomp on it and he say okay and he's looking his rear view inside mirrors downshift into first and stomp it all the way up into third gear and I never did like those Pontiac engines but I have to admit this thing did not move like those Pontiacs that I've been in because this thing really boogied and it would pull you in the seat you know we're like your eyes get a little bit big because I guess instinctively you know that if a car pulls out you're dead that's how you know a car has power and they used to make a big deal out of those GTOs from what I understand they were the king of the street for a while and then that's when pretty sure Chevy came out with the Camaro and then everything blew up from there of course up until about 1971 and that was something of the peak and then 72 is when the smog shit appeared and that was it for the muscle car age.

[@Boostlee2023]

….. cool story bro

[@imaouima]

I think you meant 389 in your GTO, not 383. Next time sprinkle a few periods in your paragraphs.

[@FIVE-0-APOCALYPTO]

@@imaouima yes, 389 tri-power, Muncie close ratio 4 speed, all factory options including 3:55 posi type configuration rear end. The reason for run on sentences and retarded context, is because of the retarded voice/text recognition of recent years and my unwillingness to simply type out my thoughts, unlike today. Thus, ....the more reasonable and intelligible, contextual body and paragraphical structure. Aint that right bwoy....IN'IT BWOYYY?

[@duster0669]

Wow! You young guns are not very bright lol. They used to teach this stuff in High School, Jr High if the guy was smart. And all of the best car magazines covered this ALL THE DANE TIME! You young people are loosing a lot in this "NEW AND IMPROVED SMART WORLD!" I can tell by watching this guy you all are none to smart. There is a lot to be said for seat of the pants tuning, listening, learning to read spark plugs, and owning a stop watch.

[@ThunderHead289]

Dude, I’m arguably the best carb/ignition timing tuner on youtube. If anyone thinks they can outdo me, It’s always an open invitation.

[@joekaz5198]

Ok grandpa, let's go find your pants

[@brokeassgarage209]

If I had the money I'd pay ya to come fix mine up here in Pennsylvania... I really need a buddy to go through this engine.