1979-1993 & 94 Conv [Subscribe to Daily Digest] |
Base boost is what the turbo will give you without the APC bleeding off the boost signal to the turbo wastegate.
So the idea is to stop the apc from bleeding air to atmosphere and fooling the turbo wastegate.
One way is to simply pull the electrical connector off the APC solenoid...the three way valve near the coil on the radiator support. That way the turbo wastegate sees engine boost and will open at base boost...should be about 6.5psi on my 87 900T.
To set the base boost, you simply measure how much boost you're getting...run up to 3000 rpm in second gear and push on the brake and the gas pedal at the same time. Look at the gauge you installed temporarily to measure boost in psi...don't hold the brake for more than about 5 seconds, the idea is to hold the car from accelerating with the brake while boost builds enough to trip the wastegate. If you're not getting the spec you have to adjust the wastegate length. Shortening the length is more boost...more boost has to occur to push the rod to open the gate (or vice versa..I have to look at the can and see which way the port is on the diaphragm). Supposedly you can do this at rest in first gear with an automatic trans by stalling against the torque converter but I wouldn't do it with mine, I'll tell you! With a standard, the brake/second gear (or third if you want to do it at higher speed) trick or a dyno is the only way to do it. I guess you could use a mityvac or air compressor/regulator that could adjust/supply up to 10psi and then measure wastegate opening, but that would just give you a starting point...it only matters what the engine sees.
You shorten the rod by disconnecting the rod from the wastegate, holding the threaded rod and turning the wastegate end of the rod. Do not let the rod turn at the diaphragm, it will rip the diaphragm. It used to be 1/2 was 1/2 psi or somesuch...you'll probably have to experiment a little.
posted by 68.55.43...
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