[Diy_efi] RE: Banjo Dis. Pic

[Greg Hermann]

At 7:43 PM 1/14/03, Mike wrote:
>At 01:51 AM 13/1/2003 -0500, you wrote:
>
>>If your talking about controlling boost with the normal butterfly in the TB,
>>the turbo would create much more boost in the IC pipes than the intake
>>manifold, creating a low-airflow high-pressure ratio situation, which
>>usually means inefficiency or surge. Or am I missing something? Seems like
>>you don't want the turbo to do any more work than it has to - after all,
>>more work requires more exhaust pressure.
>
>No. Because throttling the TB reduces exhaust flow which reduces
>inlet pressure - its a wonderful feedback system in that the
>effect you are describing is dynamic with a very short delay,
>if it is a problem then just use a blow-off valve but I doubt
>it reaches that stage and of course it depends a little to
>how large the intercooler actually is. I think, we are led into
>a somewhat false sense of security by virtue of commercial issues
>when we have a wastegate bypassing flow around the turbine, in
>general control systems parlance it makes les sense to do it that
>way - but is justifiable (so far) because we don't have fly by
>wire in general user
>
>rgds
>
>mike
>
You hardly would need drive by wire to control either a blow through OR a
draw through throttle in the manner you describe.

Sometime take a peek at the throttle linkage on a Holley 2300G or 4150G
(governed medium truck carbys).

The accelerator pedal controls maximum throttle position in the usual
manner on these carbs, but there is an extra spring loaded piece built into
the linkage so that a centrifugal vacuum switch (located in the dizzy) can
closoe the throttles partially to completely--without affecting the feel or
position of the accelerator pedal-- when maximum engine speed is reached.
NO reason this sort of a control could NOT be actuated by boost level,
leaving no need for drive by wire.

Regulating either a draw through OR a blow through throttle in this manner
would, however, create a situation where the compressor was being run at a
higher pressure ratio than otherwise necessary at times, thus raising the
IAT, and obviously , therefore, lowering efficiency. And, in the case of a
blow through, pushing the compressor closer to, if not into, surge.

Greg



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