Aerochargers etc: real back pressure numbers

[Tom Sharpe]

Frank F Parker wrote:

> > > Twice the exhaust BP than boost pressure ? So you're saying your exhaust has
> > > 30 PSI backpressure ?
> > >From reading "Maximum Boost" by Corky Bell, this sounds plausible.  I
> > believe at one point he says that "after the crossover point, when boost
> > pressure surpasses exhaust backpressure, you can start to make serious
>
> Corky told me typically 2/1 or worse especially on some factory systems
> where they use tight hsns to prevent that horrible "turbo lag".
> I asked some other known experts at SEMA a couple years ago and got
> similar answers.
> Being curious and since I was allready using a 12 channel datalogger and

Hurray for Frank,

>From my experience, IF the parts are sized correctly, exhaust back pressure will be
a little less that boost (assuming that you are in the efficient part of the
compressor map). anything else, and exh. press will be => than boost. (PS
Intercoolers help - takes less power to turn the compressor).  this is good. 2x
boost is bad...
Also, boost range will be 2x, that means if it starts @ 2500 rpm, it's probably all
done past 5000 rpm. Waste gates, V-Vane are solutions to this problem. Size the
compressor for your required HP and rpm (air flow) and change turbines and exhaust
housings to get the req. boost, like changing blower pulleys.  And you will have lag
under some conditions, but not others - learn to live with it. When things are
right, the boost gauge looks (and feels) like it's connected to the throttle.  Tom

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