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Re: SVO - svo Digest - V01 #50



On Tue, 9 Dec 1997, Brian Knowles wrote:

> 
> I'd been thinking that with a cam on a blown engine, that the idea was to 
> open wide and early, blow it as full as possible, touch it off, repeat 
> often.
> 
> Youl'd want little overlap, and increases in performance would be thru 
> more volume/pressure (bigger, badder blowers) or increasing RPM.  Cam 
> timing wouldn't be real agressive here, 'cause cylinder filling would be 
> more a function of manifold pressure than intake tract resonance, so open 
> early and close the exhaust early.  Is this the right track, or am I 
> making some fundamental mistake here?

Only in that turbo motors and blower motors are completely different
animals...

On a turbo motor, you have to keep in mind that under boost, the exhaust
manifold pressure is roughly *double* the intake pressure, while with a
blown motor, it's the same as with a normally-aspirated motor.  The back
pressure comes from the turbo, not from the manifold, and the more boost
you run, the higher it goes.

That's why I think that the exhaust timing is more important than the
intake timing -- you need to effectively clear the cylinder of the spent
charge, but as long as you're "in the ballpark" with the intake, it's not
gonna make a big difference -- that's what the pump is for.

got some new mail...:)

Talk to you later,
Joe Morgan