Throttle Body Size

[kleenair at ix.netcom.com]

Jonas Hageberg wrote:
> 
> Nice formula, but can anyone explain to me why the throttle body
> size is important in a plenum intake EFI system? In my opinion, it just has
> to be big
> enough to let the required amount of air in, since you do not need a certain
> air speed to keep the fuel atomized, and the acoustics/tuning is maintained by
> the tubes connecting the plenum and the intake valve.
> The only problem I can imagine with a too big throttle is unlinear throttle
> response.
> 
> Can anyone explain this to me?
> 
> Regards Jonas Hageberg

Hi,
If the throttle body is too small, obviously you will limit maximum air 
flow.  If its too big, at lower engine speeds it becomes difficult for 
the driver to control engine output (i.e. barely openning the throttle 
results in significant air flow increase).  This is especially a problem 
if you are trying to drive a high power, low weight car in rain or snow!

One inovative solution I have seen to the low throttle angle flow problem 
is a lip incorporated into 1/2 the circumference of the new GM pick-up 
engines.  Effectively, for the first 20 degrees of throttle openning, it 
limits the air passage from 1/2 of the throttle blade.

Best Regards, Mazda