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AFM744 AFM744 is offline
Cynical Misanthrope
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Join Date: Dec 2001
Location: Campbell, CA
Posts: 382
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This is an inherent characteristic of this engine, and I believe the real culprit in why so many 930s meet their demise tail-first.
The cause (IMHO) is that with this primitive mechanical/pneumatic boost control, when you lift off the gas the BOV relieves the intake pressure (good), but nothing relieves the exhaust pressure. The wastegate is slammed closed by the high intake vacuum so the immediate and abrupt result is heavy engine braking. This braking torque transfers the car's weight off the wheels it is loading, and the triple-whammy of causing abrupt positive camber on an unweighted, torque-loaded wheel. May as well yank up the handbrake!!!
I plan to address this characteristic with a very soft WG spring and electronic boost control along with the EFI in hopes of allowing the WG to relieve some exhaust backpressure when lifting. The more modern turbo cars I've tuned have way less of the driveline-shocking, inertia-reel-testing lift-throttle braking you observe.
X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-26-2008, 11:09 AM
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