1996 LT1 T/A

mods:
6 speed manual
motor rebuilt 3k miles ago
LS1 aluminum driveshaft
Electric water pump
58mm Throttle body
Racetronics upgraded fuel kit w/Walbro 255lph pump, 42 lb injectors
LE2 Heads and ported intake by Lloyd Elliot
Roller rockers, hardened push-rods w/hardened guides
SFI superdamper
McLeod billet flywheel & RAM HD clutch
Full length stainless steel headers w/Magnaflow exhaust
SLP intake

cam specs: 230 x 236 .592 lift (w/1.6 rr), 108 LSA

With that being said, i've talked to PCMforless who did the tuning and a couple of local shops. Also PCMforless said that the PCM advance timing is good. They all say I should be putting down 400-425.

The car dyno'd the EXACT same with 87 octane and 93 octane in it. AFR @ WOT is 12.5-12.7. Fuel pressure checked good. Leads me to believe that I might have a false knock because no change in power from 87 octane to 93 octane. Which means that timing isn't being advanced.

I have aftermarket poly engine mounts and a lot of vibration in the car from that and the cam. So I don't think thats helping the situation.

Any help/advice is greatly appreciated.

 

Are you seeing any KR @ WOT? What's with the blip? Fuel pressure? Dyno conditions/operator/corrections?

 

fuel pressure was 43~ at idle and 50+ when going WOT. dynos were done in the same week, correction factor of 1% both times. and i know it's not the dyno because my daily driver 2.0t GTI put down 330 wheel. >_<

I have no idea whats going on with the blip, all parts/motor rebuild was done 3-4 thousand miles ago. spark plugs are autolite 104 gapped to .035.

as far as KR @ WOT, i have no idea how to check that on a obd2 lt1.

 

update: did some more digging, car has lt4 knock module but stock knock sensor, would that cause any issues?

 

IIRC, sensors are all the same. Only modules are different. You should be data logging the dyno runs and you would kow for sure.

 

what do you guys use to data log an obd2 lt1?

 

update: i borrowed a obd2 scanner from the hobby shop on base and did some 2nd-3rd gear pulls. timing stayed between 30-40~ degrees during WOT. which leads me to believe...

I can't have knock retard because:

its not possible to have knock retard AND timing advance right?

car is hard to crank when I run it hard and misfiring under a load according to the dyno.

the spark plugs, wires, cap, rotor have been replaced, the only thing left stock/never replaced is: optispark.

is it possible to have the PCM say "give me 40 degrees of timing" and the PCM not to be able to tell if the ignition system is actually doing it?

 

Wrong.

Timing advance will typically be in the 32-40deg range. If you have knock retard, the knock retard is DEDUCTED from the spark advance. In other words, if the PCM calculates a 40deg advance from the timing table and the various offsets, the scanner would read spark advance = 40deg. If, at the same time, you had 10 degrees knock retard, the scanner would read 40deg advance MINUS 10deg retard = 30deg advance.

So yes, you will still have spark advance when you have knock retard, just not as much as you should have.

Can't your scanner read knock retard?

Use AutoTap to data log.

Does the dyno shop have a wide-band? If so, have it used and plotted at the bottom of the curve.

Why is your fuel pressure so high? Did you tell the tuner you were running greater than normal fuel pressure?