Aerochargers etc: real back pressure numbers

[Frank F Parker]

> > 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
wb NTK to tune the Typhoon I had just purchased with its new Garrett
TE-60 turbo, I instrumented the TY with pressure sensors and EGT probes
to measure back pressure before the turbo and manifold (boost) pressure
as well as egt before and after the turbo.

Was talking to Harry at PTE at the time about getting a SppedPro for the
TY and another project with a Northstar, and he offered a new "hi-perf"
turbine housing for test that he had developed for the GN world and which
had shown on the track to be worth about 0.3 in the quarter. He suspected
it would show lower turbine back pressure and boy, did it. Results below:

Old TE-60 ( stock 0.63 hsn ) ,  0-90 mph run

	turbine inlet pressure:	23.8 psi
	manifold pressure:	16.0 psi
	Ratio:			1.48   much better than previous experts
					would have led me to expect but
					the TE-60 is a very hi-po turbo.

TE-60 with PTE 0.63 high perf turbine hsn,   similar run

	turbine inlet pressure:	16.5 psi
	manifold pressure:	15.2 psi
	Ratio:			1.09	Vastly improved and before u ask,
					it did result in improved accel
					especially at high end.

	EGT at 1/2 shift:	1500 deg inlet,  966 deg out
	EGT at approx 90:	1538 deg inlet,  1088 deg out
	A/F as measured by datalogged NTK box:	12.4 a/f (kinda lean)

	Temps out turbo (before IC): 126 deg start, 197 deg end run
	Temp into motor ( mostly stock water/air IC ): 120 deg F


2nd run with PTE hsn:

	top 2nd:		1531 deg in, 994 deg out
	4th gear		1573 deg in, 1130 deg out

This run the a/f was a little leaner at 12.6 and raised the EGT's at both
sides by 30-40 deg.

All pressure sensors were quality SenSym units and temp compensated.
Thermocouples were type K and calibrated with an Omega cal unit.

Hope this is of interest to those like me who read about what things
are supposed to be ans what they ended up being in this one instance.
As they say, your results may vary.

Frank Parker

92 Ty
89 S-10 V8
65 Corvair/Northstar
2000 STS
C5R crew/engineer






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