Given this the right map is T04E "54" trim at 80,000 RPM.
Max RPM on this turbo is 115,000 RPM. Perhaps a TO4 "50"
trim might be safer also at 80,000 with max RPM 126,000.
Dave, what trim is that TO4 turbo you have?
This needs to be redone for altitude. In fact we need to do a spread
sheet or a QB program to calculate this for all altitudes and inlet
temperatures. Anybody want to take on this job?
I think Dave's inlet temperature is around 140 F as I recall.
Paul Lamar
George Lendich wrote:
Paul,
My old notes say a Garret TO4E-50 is the best suited to the 89-92 2nd gen
Turbo.
50 Trim Compressor, P - trim exhaust with modified 1.3 AR Ratio housing (
what ever this means).
Boost 6.4 psi @6,500RPM ( 43" Manifold pressure)
Boost controlled by a Turbonetics - 'Deltagate'
Small Spearco Intercooler.
Looks like we have gone the full 360 degrees here, but at the very least you
seem to know why.
George ( down under)
PS could you explain what the second line means - that was a couple of years
ago.
A TO4 probably is best suited but that is not to say a stock 89-91 turbo
won't live if the boost is limited and the waste gate is ported.
A jump from 30 inches of Hg to 32 inches of Hg is a 13% increase
in RPM and stress at the same altitude. On top of that the engine is generating
roughly 6% more HP and heat so the temp goes from say 1600 F to 1690 F roughly
which further reduces the max allowable stress on the turbine wheel.
BTW the reason the turbine is failing rather than the compressor is; cold
aluminum is stronger than hot high strength steel.
A/R is an unfortunate short cut in the turbo industry. R is the size of the
exhaust scroll and A is the area of the exhaust scroll. IMHO it would
be more clear if they were quoted separately. You can have a wide range
of sizes of turbine scrolls with the same A/r.
R is the distance from the center of the shaft to the center of the scroll
throat while A is the area of that throat. If A is increased the turbine will
slow down with a given R. You can also slow the turbine by using a waste gate
or drilling a hole in the scroll to bypass some exhaust gas.
Paul Lamar
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