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CARB vs EFI


Nate1647545505

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In a good spirited, gentleman discussion on engine management:

 

 

An engine is put on a dyno. The only things that are being measured: peak horsepower and torque. Drivability, emissions, and dynamics are negligible.

 

 

Two setups:

 

 

I. Sequential Multiport Fuel Injection (non direct port), Speed Density system, Individual Throttle Body type manifold

 

 

II. Tunnel Ram, Duel Split [Dominator] Carbs

 

 

Which would make more power and why?

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SFI, greater fuel control. Chevy High Performance i think it was did a write up on it a few years ago and the only thing they changed was converting the intake over to take the fuel injectors and it gained them 35+ horse with no other changes. they said it was due to the fact they could greater control the A/F ratio for each cylinder. now that i think more about it the tunnel ram would make more peak power but would suck down low. but have a tunnel ram with fuel injection it would help out the low end.
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the carb will make more HP

 

the efi better drivablitly, more torque..

 

 

and the engine it self has a even bigger effect...cam spec etc.

 

the efi isnt going to like the carb cam and vise versa.

 

spray = car

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But can you turbo a carb'd car Nate?

 

 

Yes.

 

 

So does the longblock remain the same? The camshaft design is going to have a large effect on power output do to the different intake styles. The question is rigged.

 

 

A better comparison would be the same intake however one converted to carb use, but even then the intake isnt designed for EFI use and there are distribution issues while trying to do so (which isnt that big of a deal with a SEFI setup because it can be tuned around but it will effect overall power output).

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Yes.

 

 

So does the longblock remain the same? The camshaft design is going to have a large effect on power output do to the different intake styles. The question is rigged.

 

 

A better comparison would be the same intake however one converted to carb use, but even then the intake isnt designed for EFI use and there are distribution issues while trying to do so (which isnt that big of a deal with a SEFI setup because it can be tuned around but it will effect overall power output).

 

Rob,

 

Long block remains the same. Cam profile is also the same. I concur on the question having a hole when it comes to changes and optimizations in the manifold. Would it be fair to say: Each setup runs anifolds optimized for their respective air/fuel management?

 

A question that bounces around in my head:

How much (if any) pressure drop @ the Venturi is there on a race carb setup? How much will it effect performance (if it does at all)?

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But can you turbo a carb'd car

 

yes... charged or turboed

they are called blow thru carbs..

 

visit turbomustangs.com...they have a complete section on modifying holleys for this, plus there are carbs built just for it. like this one..

 

 

http://i5.photobucket.com/albums/y196/gearhead559/100_0827.jpg

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Errrr, this again. With ONLY wide open throttle being a concern, they are dead even. The manifold design will play into it some because one is more designed for wet flow and the other dry so taking a tunnel ram and drilling it for injectors and running throttle bodies on it and not carbs is going to have mixed results. But if you are taking money be damned, intake and fuel system on the same long block, they are dead fucking even. You need to remember that they both do the same thing, regulate air and fuel into the motor and keep it in the right mix so the motor can burn it and make power. the motor doesn't care what's on top it, it just wants to see the right amount of fuel and air for a specific horsepower level.

 

The minute that it hits the street and you are talking about part throttle performance, while a carb can be tuned for it, it's where EFI shines because it will self tune if it's a closed system and it's tuned close. Carbs will go rich and lean through the throttle opening because they use the air flow through them to meter the fuel. Problem is that if you are at part throttle and you mash it, the air flow almost stops through the carb hence the need for an acclerator pump to richen the mixture so the motor doesn't fall on it's face. With EFI, the fuel is being sprayed on the back of the valve under pressure, its' going in the cylinder even if the air slows down.

 

Carb's are also effected in a weird way with nitrous and it depends on the size of the shot as to how it reacts. An smaller shot will create a small flow increase in the carb because of the nitrous entering the manifold at such a high pressure. But if a big shot is in place, it can easily fill the intake with nitrous and fuel and make the air flow in the carb stop because the intake is full and the air has no where to go.

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