Question for those running EFI ITBs

I normally belong down in the RCR section (have an SLC), but this question seems to belong in this area...

We have Sprint Cars in our house. Even years in, I am amazed at the throttle response of these cars. I attribute it to 1) Injection system and 2) Lack of flywheel effect.

For outsiders, Sprint Cars run mechanical injection with stacks, methanol for fuel, and have no flywheel/clutch/transmission/etc. There is simply a U-Joint bolted to the crankshaft.

Obviously the lack of flywheel effect on these cars is part of the great throttle response. Also is part of the high idle speed required to keep it running. But I have had carburetor cars with a light weight aluminum flywheel and they were not close to the Sprint Car even when making similar HP on the dyno.

So if the injection system is a big part of the great throttle response, how much of it is the individual stacks (and huge bores), and how much is the mechanical injection?

For those unfamiliar with mechanical injection, basically the 'correct' amount of fuel is delivered to the injectors, but a bypass bleeds enough fuel back to the tank to keep the engine somewhat happy at part throttle. When the throttle snaps open the bypass is closed, so more fuel is immediately pumped in. They tend to run quite rich at anything other than full throttle - though there are ways to address that if needed.

So my question to those with EFI ITBs is.... Do the EFI ITB setups have awesome throttle response compared to a carb or more traditional EFI?
 

Terry Oxandale

Skinny Man
I would hazard a guess that correct A/F ratio being the same for both (EFI vs Carb), same fuel, and same bore sizing, that the "response" would be identical. I would also think the feather-weight of a sprint car has a lot to do with the "response" you write of. A well set up EFI will compensate for throttle opening rate, pressure drop, and a host of other parameters that should provide probably better response than a mechanical unit.

I'd say it was unfair to compare a carbureted car to an injected one. I've seen some damn good carburetor set-ups, but injection, especially EFI, allows to you fine tune a huge array of fuel map modifiers compared to mechanical or carbureted set-ups.

IMHO, mechanical injection is not what I would want for a street car, and best for the WOT operation. EFI allows a more appropriate fuel mapping to provide good starts, idle, and partial to full throttle operation for the typical street/sometimes track car.
 
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I run an 8 stack cross over on the LS1 in the Brabham, and yes the throttle response is pretty quick, even with a reasonable sized flywheel and clutch. ITB's will allways respond quicker than a single throttle body.

cheers Kaspa
 
I run Hilborn 8 stack EFI, 2 7/16 bore, on a 440 chev with tilton 3 plate clutch and fairly light flywheel - throttle response is very crisp. Cheers, Andrew
 
I have ran all four combinations, 4 barrel carb, weber carbs, fuel injection with common plenum and the ITB fuel injection. The is a big difference in throttle response with webers or ITB's compared to common plenum designs. The throttle plate is just inches from the intake valve. I will never go back to a common plenum design. Running on the track is not about peak HP but how quickly you can to the HP you have. ITB's will help with that.
 
I would hazard a guess that correct A/F ratio being the same for both (EFI vs Carb), same fuel, and same bore sizing, that the "response" would be identical. I would also think the feather-weight of a sprint car has a lot to do with the "response" you write of. A well set up EFI will compensate for throttle opening rate, pressure drop, and a host of other parameters that should provide probably better response than a mechanical unit.

I'd say it was unfair to compare a carbureted car to an injected one. I've seen some damn good carburetor set-ups, but injection, especially EFI, allows to you fine tune a huge array of fuel map modifiers compared to mechanical or carbureted set-ups.

IMHO, mechanical injection is not what I would want for a street car, and best for the WOT operation. EFI allows a more appropriate fuel mapping to provide good starts, idle, and partial to full throttle operation for the typical street/sometimes track car.

Pretty much nailed it there Terry. Going back to the mechanical set up and AF ratio`s, There were none:shocked: it was a bit hit and hope in the day and tuned for flat running . Bore wash was common with overfueling but not important in the grand scheme of things. Programmable EFI is your cake and eat it IMHO .

Bob
 
I have played a lot with sprintcars and yes the throttle response is awesome however the mechanical injection or full flow injection works back to front. you jet the fuel that returns to the tank the rest goes in the engine With all that fuel and individual throttle body's ( ITB ) Its response is excellent but it is very thirsty to the point you would never consider driving it on the street. I'm sure there are exceptions should I say I wouldn't drive it on the street. Dean's point about the plenum is valid the open area under the carb slows the throttle response. It works well in drag racing where the throttle is held open then the clutch is released. that's why you don't see a tunnel ram in circuit racing.
My GT runs computer controlled ITB and a light flywheel and the throttle response is epic, better than all the carburettor stuff we have built.
Bob is right EFI is your cake and eat it too
IMHO
Woody
 
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