| temperature drop through the turbine with the given airflow and acceptable EGT passing through the .64 A/R turbine housing to provide the required power to the compressor to achieve peak boost; even with a 3.0" exhaust. Dropping the exhaust after the turbine (no downpipe) would improve this condition by about 1psi perhaps, but the biggest factor is the housing's geometries. The throat area in the .64 A/R housing just doesn't bring the exhaust gas velocity and density high enough to provide ample power for the turbine to drive the compressor to its peak. To date, there are no .64 A/R'd GT2860RS turbos producing more than 28psi of boost on a VG30, which empirically validates this. The 10-blade wheel is the next closest step to providing the required power by harnessing more of the available pressure/density coming out of the housing, but it appears that it is slightly too much in the 4-bolt .63 A/R housing and clipping of that turbine would help this condition. I'm producing a set of the turbochargers I have on my car for a customer but we are using the .64 A/R 5-bolt turbine housing with the 10-blade turbine wheel. This housing has a slightly larger frame to it (than the 4-bolt .63A/R in my setup) with slightly increased throat area, which will achieve almost the same result of clipping the turbine in my setup. In this particular case, the only thing that will be different in the turbo vs. the GT2860RS with .64 A/R housing is the turbine wheel itself and nothing else. That car will be coming to me in short time for dyno tuning and it is virtually identical to my setup, so it will be a good test for comparison.
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[ agpowers@bellsouth.net ] Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the tailor.
Albert Einstein
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