Thread: for the EFI guys

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Is there a formula for selecting throttle body size and injector size for EFI like there is for selecting carb size??? While looking at 351 Windsor intake manifolds and throttle body sizes I've noticed they range in size from 72 to 90 CM..., and a whole range of sizes rated in psi for the injectors..... just curious if EFI is like a carb and too big is bad or if the computer adjusts for the available air flow and injector size???? Performance, as always, is the issue here.... MPG is something my Escort gets!!!!!

Dave, did you mean cm as in centimeters, not CFM?
I read one build on a 300 that used a 460 throttle body, not sure if that helps. Maybe if you had the actual cfm rating for any given throttle body you plug that into the carb formula.

Ooops, yes I did! Thanks for pointing that out. I corrected my post...

Here is a guide to choosing the right injectors. Hope it helps.

(click here)

Thanks Joe, just what I was looking for!!! Never thought of checking Accell!

Dave, I posted this last night on our Harley board, the same principles apply. It doesn't answer your question completely, but hopefully, it's food for thought.

EFI and carbs are different animals on an engine, the fuel flow characteristics are different. The Carb requires air passing thru it to draw fuel out of the carb then into the intake ports, the EFI shoots fuel directly from the injectors into the intake tract near the entrance to the head at precise intervals, fuel doesn't have to flow completely thru the intake manifold like in a carb set-up. The butterfly on the EFI unit only controls the amount of air entering the engine, the carb butterfly controls both air and fuel flow entering the engine.


Mike