[Supras] boost pulling timing

[Walker, Brian (Rich. Dist)]

I'm not aware of a feature that would cause boost to pull timing, I
believe that circuit is open loop as I don't recall the ecu receiving a
pressure signal from the sensor. Perhaps it's related to an airflow
signal that pulls timing? (from my understanding the ecu should retard
timing at higher boost for safety and power reasons, I'm imaging that's
a function of airflow in the maps?)

I wonder if anyone out there has datalogs showing timing vs. boost? The
MAFT is supposed to show this info, but I haven't had a chance to mess
with mine since install. FWIW, I've never had a code for knock, even
when one sensor crumbled apart as I went to remove it.
Brian W

-----Original Message-----
From: berniek at technicaldevelop.com [mailto:berniek at technicaldevelop.com]

Sent: Thursday, December 20, 2007 12:58 AM
To: Walker, Brian (Rich. Dist); cthommes at adelphia.net; Jim Jobe;
Supras at supras.com; Jeff Mohler; Jeff Corbat
Subject: Re: boost pulling timing

I've wrestled with this issue too, running a Lex and 550cc injectors, 57
trim CT26, 3" turbo back exhaust, 15-17 PSI boost, IC upgrade to come,
some hardpipes, all with the stock ECU, trimming fuel pressure and the
Lex bypass.  In a word, the pressure transducer at least in '90 and '91
applications only operates the dash gauge, nothing more (it will operate
up to almost 15 PSI at about 14.9V output if you rescale the gauge
circuitry to match it).  That leaves the knock sensors to retard timing
if and when needed under higher boost.  I believe Jeff Corbat is running
a setup like this with a stock turbo and has had no problems.  I've had
no codes set ever (in all of 500 miles, lol, but some of it before the
snow under really punishing conditions.


    Bernie


PS:  I believe I might have an earlier ECU which might explain slight
mixture dependence upon temperature and faster idle with the lights on.

Once when I did not catch second gear upshifting in time, it spun to
6500 RPM, which '91's with fully counterweighted crankshafts are not
supposed to do.  My '90 stuttered at 6200.