Weber carbs and velocity stacks - Resonance

In this video we explain the resonance effect and how that is affected by the length of the ram pipe. ( ram-pipe = Velocity stack= trumpets) . This applies to natural aspirated engines without forced induction.
There are many video\s on my channel about the weber carb and others on how to adjust and baseline them. This is the last part that was missing....
Here is the weber playlist : • Weber DCOE tuning - M...

[@paulfisher1160]

All makes scenes. Keen to learn more on this. Especially forced air. Then how to have the best or compromised design with air filters. Keep up the work Regards, Paul

[@SeanOBryanZZ]

Thank you for the dcoe videos i have rewatched your series multiple times this year. Please do few more! Possibly driving characteristics and definitely more jet behavior with the air! My 2 issues right now is bogging on a hard launch and a lean low end on the main etube with a load. With a very gentleman like throttle application the carbs work great but if i try to force the carb to work with low air speed its lean then eventually the fuel flow catches up.

[@v2gbob]

I suppose you have tried increasing the size of the accelerator pump jet? Likewise on the idle jet or maybe you need an F7 emulsion tube?

[@D3Sshooter]

I will see what I can create, as for your pointed problem, there is a need for a certain airspeed to have the venturi effect . If the airspeed is to low , then that will not happen and you have an lean issue. On the other hand volume is also need... in many cases increasing the air volume due to wider open butterfly can or will drop the air velocity initially until the engine picks up rev's. That is why we have an acceleration pump, injecting that extra amount of fuel for two reasons. One you need more power thus a richer AFR to accelerate the car, and second compensate for the initial loss of airspeed / venturi effect when pushing that pedal down. In your case I would start with more squirting of the acceleration pump.

[@ldnwholesale8552]

Pump squirter not working

[@SeanOBryanZZ]

@@ldnwholesale8552 acceleration jets are working it's after the shot on steady hard pull it doesn't draw the on the mains until higher rpm. I already went down 4mm on my choke and have 8 different etubes and boxes of jets. And unfortunately every time I make carburetor tuning progress the chassis/suspension demands more work:) gotta love 50 year old cars!

[@SeanOBryanZZ]

@@v2gbob I have and the O2 gauge has it going extremely rich so I have been trying to mellow the shot out but bring the mains on sooner.

[@FrancoiseJacquemin]

Very very very interesting video. Hope soon the one on the inducted air boxes.

[@D3Sshooter]

Thank you

[@Loren-g5k]

Steve: As always you made a great presentation and I was able to learn something. I have heard the term "resonance" referred to in regard to carburetors but had no understanding of it. Thank you. Looking forward to the next installment .

[@matthalls2486]

Great video as always, excellent simple explanations. Would be great if you could post the calculations for a starting stack length for low, mid rev engines. Keep the videos coming, I learnt so much about SU’s tuning and AFR ratios from your teachings.

[@D3Sshooter]

Thanks. Somehow that piece of the video slipped out during the transcoding. I will need to recap that. Thanks .

[@General813]

Hi Steve, your workshop looks great with the license plates and other parts👍🏻👍🏻👍🏻

[@D3Sshooter]

Thanks

[@sluggo1958]

Great overview and explanation! Easy to follow and understand and another in the series that you've done explaining all aspects of these carburetors.

[@etienneprinsloo6799]

The one single thing I miss the most in our current age is the sound of a car with two DCOE’s on full song.

[@MLC...]

I have had classic Alfa Romeo's since I was 18, now 52. As a child my father had a Giulia Super. I have néver grown tired of the sound of side draughts. Think I will suffer from depression if I no longer have them. Scratch that itch.

[@robertheymann5906]

Explained very well, thx for the video

[@overlandready]

a lot of people don't understand that everything is a compromise, it;s just where the sweet spot benefits you more. Resonance aka fequenct of gasses is imporrtant on both sides of the engine, altering intake will alter exhaust and vice versa especially if the engine has a long scavenge time.

[@weofnjieofing]

Great video! Also, it’s better to have longer intake manifold so that the airflow past the throttle blades gets more time to stabilise before entering the cylinder. Also, the airbox acts as a low pressure zone of stable air allowing better suction effect from the resonant frequency

[@weofnjieofing]

Furthermore, air inertia is critical not just airflow as air has weight and timing that inertia also helps with optimal cylinder filling.

[@GarryCharlesworth]

Thank you. I just remembered some motorbikes had variable intake lengths, via flaps.

[@kyproset]

Excellent, thank you.

[@SuperTambo69]

Thankyou, well explained, and interesting about the air dams. Was going to do on my race car, but not now. The air box video will be good to watch

[@ldnwholesale8552]

Having used 45mm Webers over several decades the long ramtube always is better than short. No ram tube is noticeable. You have a rockstrainer over those ramtubes. Bad!! The standoff from the trumpet will be at least an inch out of the top. You are strangling it like that. I always used pod type filters with plenty of space above the throat. Many refuse to use airfilters but that is dumb,, or maybe they have strangled them. Here in Oz our 71-73 Valiant Chargers used 3 45mm Webers and that was a known fault with the factory airfilters, which were at least an inch above the short ram tubes used. Lots of fuel staining in them. With IDAs the standoff is even more.

[@AlexTrull]

Good video. Still getting my head around the negative pressure wave.. maybe do a diagram next time ? variable length intake runners are very very rare but they were on a famous car (the 787B) from what I recall.

[@emma.j.nation]

A lot of production cars have used variable length intakes, but it’s normally achieved by having two different length intake runners with a valve that switches between them at different rpm ranges. Also, you can get adjustable length ram pipes, though they’re obviously not adjustable ’on the fly’, just for tuning on the dyno to optimise where in the rev range you want torque

[@D3Sshooter]

I will create a animation for it

[@Tom-z1q]

Your a real gentleman. I did enjoy this and thank you. At the end of this presentation. You talked about forced inlet pressure reducing the filling eficeincy. I will have to watch this again to be sure I heard you corectly. But if I did. I think you have your inlet pressure theory wrong and no measure that I have ever seen. Can added inlet pressure from a scoop or charge inlet ever hurt intake eficiency? I am not convinced. But I do really appreciate your input and wilingness to share information. Thank you.

[@D3Sshooter]

Thanks, It seems that I was not clear enough: What I was trying to say was that the increase in pressure around the trumpets due to an airscoop can prevent carburetor resonance. Which does not mean that the additional pressure due to the scoop is not going to help filling the carb. It will do so, but eliminates the resonance gains...in full or partial... I am not talking about forced induction systems, I am talking about natural aspirated engines

[@Tom-z1q]

@D3Sshooter thanks for clarification. That makes more sense now. I know you were talking N/A. So was I. My reference to positive pressure at the induction inlet. would be increased ambient pressure density do to the vehicles forward velocity. I was not refering to any kind of added boost device. Anyway, thanks again! Great video.

[@D3Sshooter]

@@Tom-z1q Thanks Tom, indeed... the entire matter is a very complex one and trying to put some simple explanations in is not always easy... Have a great day...

[@giorgios16]

Do a video on airboxes !!

[@AxsWeber]

Hey Steve! I just bougth some velocity stakcs for my Weber 40 DCOM for my AX Sport, it's a very rev happy engine with peak toque/power at 5000/6800 rpm but I feel like I want more grunt in mid rpm, would a 35-40mm long velocity stack be a nice choice or should I get longer ones? Im afraid I loose peak power it makes about 100hp with the stock airbox will I loose hp by fitting some semi long velocity stacks? Cheers!! Love your videos and thank you so much for sharing your knowledge, I learned how to tune my webers with your amazing videos!

[@pum882]

You got the physics behind the resonation completely wrong. First of all the wave which travels backwards doesn't disperse in the atmosphere, it actually bounces back towards the valve. The intake runners are "tuned" to a specific engine speed, when the timing is such that the wave travelling from the entrance of the velocity stacks hits the valve when it's open. This is the most favourable condition as the positive pressure helps the engine to intake more air fuel mixture. On the other hand if the valve opens when the wave is far for it, the engine will suck less air because of the negative pressure wave at the valve. This is the reason why different lengths of the runners make more or less power at different engine speeds

[@D3Sshooter]

Not really, i thin k its a matter of wording. The reflected high pressure wave does indeed bounces back ,but that is the negative pressure also called the rarefraction. When I stated that it disperses in the atmosphere, its trying to explain that high pressure wave ( the reflected) transforms into a rarefraction ( low pressure return wave). and the rest of your comments are also what I stated ... I will make an animation on this so we can further discuss it if you like.. Thanks for your comments, its always great to discuss in a polite manner

[@unfinishedthought]

I already learned so much on your DCOE series- can't thank you enough. I rebuilt a set from your teaching and fitted it to my (already heavily tuned) Lada 2103. May I ask where you are from?

[@TheNaki4a]

Great video! Is the video cut off? (didn't get to the calculation table) 🤔

[@ScottLewis901]

Great video explaining ram pipes. Would you ever recommend doing that on a street car for more torque?

[@D3Sshooter]

You can do so. As long as the noise is ok. But keep in mind that this improves the performance but not with massive amounts . There are many other things that need sorting out like

[@giorgios16]

great video, thanks, so also shorter intake manifold is best suited for high rpms engine (better flow at high rpm) ?

[@D3Sshooter]

Yes indeed

[@1RickSanchez]

Great video! I have a few questions. For 2 stroke, would I just double CFM? Would I also just use rpm for finding my resonant frequency? Can I use a stack to get rid of a dead spot mid rpm without detrimentally ill effects to the top end? Thanks!

[@stevesloan6775]

How about having an airbox inlet that has a valve system that shuts off flow, timed to the inlet valve frequency. So, it creates high pressure at high car speed when open, and then shuts of flow in a timed sequenced to create steep pulsed negative airbox pressure on demand? I was always intrigued by boost bottles that two stroke engines use., and how they interacted with 2-stroke reed blocks (power band pulses) I always ark back to the old Myth Busters episode covering long tubes under vacuum (70M), that are punctured to create crazy supersonic air speeds. Thats is literally equivalent to a good valve seat in action.

[@raymondsanderson3768]

Bloody hell, they catch fire BEFORE you fit them!

[@salamander5703]

I thought part of the reason for the bell mouth shape was because as the intake draws air towards it some would be wasted as it would pass by the sides of the intake. So the bell mouth catches more air. Would be interesting to see if anyone has flow bench data to show if that works. Otherwise, would the resonance effect work just as well with a plain tube with no bell mouth?

[@vintage76vipergreenBeetle]

👍

[@erichlausch9886]

👍👍👍👍👍

[@Loren-g5k]

Another question...what is your recommendation for a fuel pressure regulator for DCOE Weber?

[@whatsgoingon8639]

Sounds similar to the way expansion chamber on a 2 stroke exhaust work

[@IMCAust]

I am curious if you have done anything with the progression holes, I have a set of triples to go on an L28 into a 240Z with the original 3 progression holes, have been told that they are horrible to tune because of the progression holes. Any thoughts please, still need to rebuild them as per your previous vids, so work to do, just figure i could possibly make a mod before install onto engine... Thanks muchly!

[@D3Sshooter]

Thanks, not in my opinion, I never had to make changes to the progression holes. Just make sure that they are open and clean, also not that the same idle jet feeds the idle hole and the progression holes, so maybe you might to increase that one..

[@jonathansanchez1305]

5:35 #rarefaction

[@gm3801]

Variable length manifolds?

[@johncrowley5612]

Kawasaki used different length velocity stacks on their 750cc WSB engines. The outer (cylinders 1&4) had shorter stacks than the inner 2 cylinders. Part of the reason was to give the rider's a bit more room around their knees but this also widened the powerband somewhat, making the bike a little more user-friendly.