Yesterday I was scanning my Dad's GTA. THe outside temp was about 108. We made three runs and recorded it with dicom. Now the first run the coolant temp was 169 (he has a 170 t-stat). This run recorded the most amount of knock seeing as much as 12 a one point. O2 where in the low 800's. Next run was 185 this run was the 2nd worst with O2's in the low to mid 800's. Knock retard averaging about 3-4 with as much as 6 at one point. Next we ran the car @196 degrees. This run had O2 volts in the low 900's with no more than 3 degrees of knock. I just thought that was a little strange. He has the stock chip so far so it would seem that he should try to run his car @ about 200 at the track. Someone told me our cars run better warm but I didn't believe them at first.

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1991 5.7L Z28 - gutted air boxes, K&Ns, airfoil, ported plenum, relocated MAT, accel TPI base, accel 300+ ignition, accel cap&rotor, homemade AFPR, derale fan switch, vette servo ,flowmaster exhaust, torque conv. lock-up switch, and fresh 255/50/16 Dunlop sp800s. More to come!

 

Your buddy's car is running lean at WOT.

At higher temps the intake charge is LESS dense meaning less O2. Less O2 means that you'll run more rich. More fuel in many cases decreases the knock.

Simply put - pump up the fuel pressure a PSI or two and then run again at 169º. You should notice more power because now you'll have enough fuel to supply the amount of O2 entering the engine. Having more fuel will suppress the knock and allow you to run with more advance .... all of that equates to more power

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.587 @ 107.97mph (1.710 60ftr) on the long runner setup.
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels. Stock Wheels. No Weight Reduction.
Gunning for NA 11's with the MiniRam II and Hooker LT Headers.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I agree with Traxion. The car needs more fuel pressure when the engine temp is cooler.

Your O2 readings (and performance) are confirming each other: not enough fuel (pressure).

You want a reading around 900 mVs @ WOT on the O2 sensor to get optimum times. A nice flat O2 reading is also desireable.

Also, watch those knock indicators too. Though they can be "false readings" they may also indicate an injector imbalance especially if you O2 readings are outside the 900 mV +/- 20 mV. One lean injector may be causing the knocks (and retarding your ignition) while the other injectors are rich due to excessive fuel pressure to compensate for the weak injector. Welcome to "tuning".

 

That's probably what I am experiencing with my car. For the mods I have it seems like I have not only had to bump the fuel pressure but increas the VE tables to almost 100% from 2800-4100 and it still hits the knock sensor sometimes. This is with a stock timing curve. Fuel pressure is @ 47 psi. Initial timing is 6*.

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1991 5.7L Z28 - gutted air boxes, K&Ns, airfoil, ported plenum, relocated MAT, accel base, accel 300+ ignition, walboro fuel pump, holley AFPR, vette servo ,flowmaster exhaust, and a custom chip. More to come!

[This message has been edited by redmet91z (edited September 29, 2000).]