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Registered
Join Date: Aug 2006
Location: Cincinnati, Ohio
Posts: 1,019
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Brendan,
You have to first pick the compressor for the engine size and then focus on the turbine. Yes...the turbine and housing for a rear mount are typically smaller than front...this aids in getting them to spool since the air has lost some temp (i.e. energy) from the heads to the back of the car. Remember, it is the heat and pressure differential driving the wheels...not just pressure as some people believe. You can measure temp drop across a turbo...that heat went into powering the compressor.
Rule of thumb...a turbo sized for front mount if mounted at the rear would be very lazy to come on boost. The air loses some temp and pulse energy at the rear, so to compensate you size the turbine and a/r down. Lots more to turbine sizing than a/r though....many turbines, housings and a/r ratios in those housings. Not an exact science either.
JK
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Kuhn Performance Technologies, LLC
Big Gun: 1988 928S4 Twin Turbo, 5-SPD/LSD 572 RWHP, 579 RW ft-lbs, 12 psig manifold pressure. Stock Internals, 93 octane.
Little Gun: 1981 928 Competition Package Twin Turbo, 375 RWHP, 415 RW ft-lbs, 10psig manifold pressure. Nikasil Block, JE2618 Pistons, 93 octane.
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