<VV> RE: Ed's strange turbo behavior

[FrankCB at aol.com]

    What Jim says makes sense to me.  When I was driving my 180 Corsa 
regularly to work years ago I measured 8 psig (pounds per square inch ABOVE 
atmospheric pressure) going full throttle up a long hill at highway speeds.  After I 
insulated the exhaust, the boost pressure on the same hill increased to 10 psig. 
 This measurement was on a 4 inch diameter Sears "tune-up" gauge that showed 
boost to the nearest 1/2 psig.  If you use the stock 40+ year old gauge to 
indicate boost you are just kidding yourself.  Using this after-market gauge 
regularly is also a good way of indicating if you develop any exhaust system leaks 
upstream of the turbo.
    The downside to insulating the exhaust was a complete blowout of the 
elbow after about 6 months due to "overtemperature" of the steel tubing.  At least 
that's what the chief metallurgist at the plant told me when I showed him the 
remains of the elbow.
    Frank Burkhard

In a message dated 1/7/06 1:56:02 AM Eastern Standard Time, 
burkhard at rochester.rr.com writes:
One big question ... look at the gauge face and tell us:
1) Does it read "psia" or "psig"?
2) When you shut the car off, what number does the boost 
gauge read?

This is a (relatively) unmolested sorta stockish car, right? 
Boost should be limited by the restrictive Carter YH carb. 
If you switch to something else, you can make more boost, 
but at these pressures (if they are gauge pressures and not 
absolute pressures) you will be scattering stock cast 
pistons even if you somehow keep it out of spark knock (at 
those gauge pressures, you need water injection and/or 
intercooling and/or active knock sensing and spark retard, 3 
modifications it seems you are implying are unlikely.

My vote is that the gauge reads psia.  Subtract off 14.7 and 
you get gauge boost pressures of between 5 and 11 psig ... 
right where they should be on a healthy stockish Vair.

Jim Burkhard