Injector Sizing: REALLY dumb question

[Greg Hermann]

>In several very recent threads, it has been stated that drivability
>problems (usually at idle IIRC) preclude the use of large injectors for
>TPI. Yet, TBI uses one or two large injectors with generally no mention of
>such problems. Would someone please tell a dumb sparky exactly what is
>causing problems with high flow injectors in TPI and why that is not a
>problem with TBI? Back to lurking in the shadows......with my 332
>controlled and fully instrumented CSH low over my eyes and hopefully ready
>for the impending  walls of flame.

Mike--

No flames here. I f you have a TPI V-8, you've got eight injectors, say
20#. Same engine with TBI has two injectors, say 80#, keeping  the numbers
easy and round. If you have the two engines set up with the same idle speed
and same parasitic load at idle, you will have the same % duty cycle on the
injectors at idle, and the same turndown ratio.

Differences:
1. I think a lot of TBI set-ups use peak and hold injectors, but don't know
for sure. Anybody else???
These injectors will get down to a shorter pulse time without going
unstable as to amount of fuel delivered.

2. A TBI setup is not required to fire each injector once per intake
stroke, so conceivably, they could go to a longer pulse at longer intervals
to take care of idle and real light loads. (Again, I don't know--do they,
anybody??

3. I don't know of anybody building a motor hot enough to get into this
kind of a problem and still using TBI on it. Perhaps the TB limits the
total air flow to the point that the injectors are not (and don't need to
be) big enough to get into the problem of too short a pulse at idle .

4. Take a Pro-Jection 4 barrel for another example. It will flow enough air
for big power, but it has four injectors. But they are staged. Only two of
them fire at idle. So it has twice the turndown ratio, just as sixteen
staged injectors would on a TPI V-8.

Regards, Greg