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I got a modified distributor advance/retard unit from Brad at KC Saab (check for his posts on the Performance BB for his email).
The stock distributor only retards 5 degrees at max boost. So, from the stock setting of 16 degrees BTDC at idle, timing will retard to 11 degrees at 11 psi boost. On my modified unit, there is 10 degrees retard. Now, if you kept the stock setting of 16 at idle, you'd have way too much retard under boost.
I ran my car for a few weeks like this though - the flywheels were changed and there was some question about the timing marks being in the same spot - they are, btw. So, my car was retarding to 6 degrees, except full boost at the time, was 20 psi. It would hold that all day when outside temps were 85F, although remember, I also have water injection that comes on at 10 psi. Once I advanced the timing to 20 degrees (so 10 at full boost), it wouldn't hold 20 psi anymore. If I set the APC so that it tries to achieve 20 psi, it will get there, but the APC will typically almost immediately drop the boost back, anywhere from 5-10 psi, depending on just how fast it got to 20.
I have found a 'magic' setting for now, but it's only producing 17 psi max, and that only under 4000 rpm, above which point I get slow taper. The magic however, is the fact that it no longer gets cut back by the APC. I haven't taken it up to redline yet, but it looks like it will probably taper to about 11 psi. I don't think this is bad at all, considering that was the max boost before, and there was even more taper with the stock APC.
Anyhoo, I will probably do one of two things from this point - 1) adjust the APC in minute increments until I reach a point where it is starting to kick down the boost from maximum, or 2) advance timing until the same occurs. Either will give me more power and torque, so I am leaning towards the timing at this point, especially since advancing the timing will help low end response, while increasing boost will only help response after the turbo has spooled up, which is no less than 2700-2800 rpm.
Aaron Gilbert
1987 9000T 275k miles
posted by 207.202.17...
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