Effects of camshaft timing on turbo spool-up

[Camden Lindsay]

Hello,
I'm sorry if this is not EFI enough to be considered on this list.  If you 
feel it is not, please email to me personally....

I was wondering if anyone could tell me why camshaft timing effects turbo 
spool-up--

On my audi (83 turbo motor)  peak boost stock occured at appx 4500 
rpm-6000rpm (8-9 psi, manual wastegate... that is, just a spring, not 
electronics..)... I had read on audifans that retarding the cam (maybe i 
have this reversed-- maybe it was crank retard-- but don't remember) would 
cause spool up to be earlier, which i investigated (purchased an adjustable 
cam gear).  Indeed it did-  by retarding the cam timing 16 degrees or so, 
(which is what they said to try it at first) the peak boost dropped to about 
3000 rpm and the high rpm boost dropped significantly (so it was about even 
with the  3000 rpm boost, which was 5-6 psi)

The main thing i noticed was the wastegate popping ALOT earlier (3k rpm)... 
so what'd i do...?  Put a stronger spring in!  After that it ran 8-9 psi 
from 3k to 5.8k or so, with a small taper above that.

The only thing i could figure was that, with cam retard, the exhaust gasses 
are getting pressurized a small about by the piston before their release 
throught the valves, somhow increasing exhaust velocity.
Is this phenomenon caused by the exhaust velocity, with the taper caused by 
turbine efficiency? Or is the taper caused by the VE of the motor dropping 
at the higher rpm because of the aformentioned (piston pressurizing exhaust 
more/not as mutch time for intake)phenomenon?
If that is true, wouldn't this be a way to compensate (within reason) for 
using a larger turbo on the motor?

Thanks for any insight,
Camden

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