Small Dual Carbs deliver more Torque than Larger on Stroker?

[RailBoy]

Hello, looking for some info to maybe verify what I have read and heard on how a smaller carb can deliver more torque than a large carb at low RPM's?

Thing is, from what I know, is that a smaller carb can flow better with the corresponding valve size than a larger carb at low RPM's do to a larger carb can run richer I believe at low RPM's. That is if I have it right.

Thing is, I do know a larger carb can flow better at high RPM's(above 5,000 RPMs), for a smaller carb can starve the engine for fuel. But in my situation, I am not looking for high RPM's, above 5,500 RPMs, but verifying more torque can come from the smaller carb at low RPM's..

So, what have y'all heard and read? True? Hope y'all are having a good day.. RB
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[quote="smitty24"]"HELP, I ported my own heads and now have fire coming out my ass" .[/quote]

[Emeraldlion]

There are going to be more educated replies to explain the why to you you I am sure. My understanding is that the appropriately sized carb to your engine displacement, cam choice, and valve size will create better throttle response and give a smoother running and transitioning engine throughout your power band. It has do do with not only venturi sizing, but also throat sizing butterfly sizing and vacuum being pulled. A lot of flow dynamics of which I am not qualified to speak to. The answer to your question though, will most likely be yes, if your engine combo is built by a power band below 5500-6000rpm you will likely not need a big carb. Your terms are relative/subjective though. Please give more information on your intended engine combo, heads/valve sizing, stroke, bore, cam selection, and the wealth of knowledge here can help size your carb.

Cheers!

[Frank Bassman]

Carb sizing is traditionally determined by flow. Larger displacement means more flow, all else being proportional. Since the piping of your intake is not continuously varying in size, flow CAN be determined by your manifold and exhaust. Ideally these items when properly designed are made such that they agree with the potential of your motor CC, head, cam, etc.

Carbs also do not continuously vary in size except for "progressives". Let's limit our talk to single barrel per runner types for simplicity's sake.

For a street car that must perform well up to 4 or 5k rpm you want a carb size that will see good vacuum to pull fuel from all its circuits properly in the "low" rpm range. Too small and you lose top end. Too big and low end becomes untuneable. Yes, flow velocity must be kept within an ideal threshold for the carb to work its "best".

Personally I prefer to err on a fractionally smaller size than larger.

I once ran a 30 pict 2 on a 1600. Great throttle response but jetting was way off for such large vacuum on that engine.

I'm looking forward to read what ray, modok, alstrup and dave have to say on this.

-Frank

[Emeraldlion]

Frank, not trying to be a you know what, and I do recognize that our carbs that we typically use do not vary in size. Just for some info for those that may not be aware there are carbs with variable venturi's. You may know this but just want to out it out there.

[atticus finch]

[Paul.H]

You would get better air/fuel mixture at lower rpm and better throttle response with smaller carb but you wouldn't gain much velocity at the port especially on a stock PICT manifold. It's mainly the manifold and port that dictate the low speed torque characteristics of an engine.

[mark tucker]

personal;y i think a lot of this is tuning issues or lack of tuning. yes you can over carb a engine,yes you can under carb a engine. funny thing diesels with thier massive tq are wide open....at idle and low and mid and wfo..... i wonder how they even run like that . Build your engine to do what you want it to do. use the right parts for the intended application. there are intakes with long runners, short runners, big runners, useless humongus runners, small runners etc, pick the one that will do what works for the desired result not for the bragging rights and have a turd for driving pleasure and tuning headaches. dont use a 1 3/8 header on a 2332 and dont use a 2" header on a 1600. 6.9 cr may be fine for a turbo/forced induction but sucks for a NA engine. if your racing desert races dont build a F1 car...unless your at the road course in Austin...and if your racing at the road corse there you probably shouldent try to qualify a mud truck...unless the race is in the parking lot....after a monsoon...( Like gainsville fl in march 75% of the time, it is quite fun!!!).

[FreeBug]

Well, sorta.

You can get better throttle response, better airspeed through the venturi, and maybe a smaller volume in the intake manifold, and maybe as a result better atomisation...but there's more to it than that

What is torque? It's just an expression of the pressure produced by the combustion. So, in fact, your ability to produce high combustion pressures would be increased by using I.R. and 4 carb barrels, or fuel injecttion with long runners from the plenum.

The thing is this will affect how the throttle works: how much area is exposed vs. pedal movement, and that will change throttle response. But this is feel, not numbers, and the facts are thaat if you size your carburettors and venturis wisely, you will almost always get more torque from I.R.

then there's the quality of combustion, how much internal turbulence, how much entry turbulence, how much squish, shape of chamber, surface texture and area of the chamber, plug placement, whether the fuel has had to travel far or not, was it heated on the way or not, how finely was it atomized, how much was vaporized before it hit the chamber, how much after, etc...it all adds up to "torque"

[RailBoy]

All the replies have been in a positive direction that a smaller carb can deliver more performance do to the above. See, this is what I have read over the years, and like a nicely tuned Single on the right intake on a stroker can deliver more torque on a stroker as well. Or, did I hit on it with all the small carbs? OR, do the same telemetry aspects not reflect the same? Also, dual carbs vs. singles? RB
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[quote="smitty24"]"HELP, I ported my own heads and now have fire coming out my ass" .[/quote]

[Emeraldlion]

Don't take this to mean a smaller carb is better in all situations. You are simplifying the issue too much. You need the right carb for the right application. Duals, singles, sidedrafts, downdrafts, idf's, ida's, drla's, there is preference, performance, efficiency, airflow and on and on. Like Mark said get the carbs that work for the intended purpose. You can't just slap on a tiny carb. For an extreme example let''s say you customized a carb from an rc plane to a 1500 single port manifold. It would never run. Engine would be choked. Your carb can be too small and the performance will suffer.

[veeweeman]

That's why a lot of bustn owners prefer the single port heads
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Never be a follower...Do your own thing, make it your own!

[jpaull]

Your title should specify single small carb on a stroker, as thats what your description says.

If this is true, everyone should toss their dual carbs in favor of a single so they can get more torque.

Put a single 40 on your 2180 and see if your torque goes up😂

[vwracerdave]

railboy you need to give all the engine details. Everybody thinks you are running a single carb or a stock carb.

There is no way a smaller carb can produce more HP or torque than the correctly sized carbs. A single carb will never produce more torque that a correctly sized and tuned set of dual 2 bbl carbs. If that were true then every racer would run a single carb on their race car.


The carbs you have now are too small for the engine combination you have.
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[FreeBug]

[RailBoy]

Basically the info was covered above that I have seen over the years that a smaller vent carb can have more power at low RPMs meaning throttle response/feel than a larger carb at low RPM's.

Thing is on the Single, I believe I have seen that work for the Single Carb was on a 2110 that never saw RPM's above 5,000 RPMs really. And yes, it was in a Rail, but it did pull hard, like 0-60mph in under 4 seconds.

But yes, when it comes to a smaller vent carb on a stroker, the info has been covered above that I have seen vs. a carb with a next size up Vents.. And yes, I know valve size, cam, chambers, and all effect this, but just did not or do not know if it is a rule of thumb that this is true for most all applications pertaining to low vs. high RPM Stroker engines..

By the way, never said stock carb or stock engine, but example seams to still play..

Thanks for y'all's time.. RB
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[quote="smitty24"]"HELP, I ported my own heads and now have fire coming out my ass" .[/quote]

[vwkirb]

The carbs have to be set up correctly for the engine. Changing the vents in IDFs might as well be changing the carb completely. Velocity is one thing, jetting is another, as is the vacuum signature of the engine.

Is this a conversation we would be having about IR Fuel Injection? I don't think so. As long as the setup matches the application then it really doesn't really matter. The real problem is that most people don't stop to think about their application, they just go big and stay home.
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Andrew Kirby