I have a '94 Z28 and a NX kit. Whenever the initial crack hits, massive knock is detected. I have it jetted at a 75 shot. Have both an AutoXray and LT1 Scanmaster hooked up. The O2s are reading fine but 8-10 degrees of timing is being pulled out because of the knock detection. Have tried 110 fuel but made no difference. Anyone care to share their thoughts?

 

No solid evidence/testing/numbers to this, but my understanding is the initial Retard comes from the sudden increase in cylinder pressure, due to what causes who knows?

Are you getting 8-10 initially or the entire run?

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Kurtis Tamez
LT4-396.com
97 Z28 LT4-396
94 Firehawk LT1-396
Team NW F-Body

 

Are you spraying before or after the MAF?

 

The 8-10 is initally then goes down to about 3 degrees towards the end of the run.

It is a wet kit being sprayed after the MAF.

 

do you have any kind of ign retard control?
MSD box or such? If so try pulling a little more timing out when the system hits, pulling 4-6 degrees with the box is better than the KS pulling 8-10.

 

Just go buy a mustang you sissy.

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James
95 Z28 M6
-355 forged 11:1 motor, 3.73 gears, Star spec II clutch, Port/Poished heads, CC305 Cam, 1.6RR's, Pacesetter headers and Y-pipe, 3" cutout, Pullies, Homemade CAI with K&N, Ported/Polished MAF, Blocked EGR, Throttle Body bypass, LT4 knock mod., Accel adjustable fuel pressure reg., Hypertech Power Programmer, Hurst short throw with short stick, Airlift air bag, LakeWood lower control arms, LakeWood adjustable panhard rod, 1999 corvette wheels with carbon fiber inserts, Silver badges, Nitrous Works Wet kit 125 shot

 

No, I don't have an ign. retard control. Do you think pulling a little out before would solve the problem?

Thanks James

 

kind of a dumb question but, are you running colder plugs and what are you gapping them at?

 

Not a dumb question. I have the ngk tr6 plugs gapped at .035. I'm still at a loss.

 

Does anyone else use a scanner while spraying? Anyone ever hear of this problem?

 

I had the same thing going on. Here's a few things I did to eliminate the problem:
The first thing I did was convert to dual stage to lessen the initial hit.
At the same time I added window switches for both stages. And put in a fresh set of TR6s. The problem went away completely for a while. Then It started happening again. So I came to the conclusion that NGK tr6 were not cold enough for my application. So I switched to Autolite 103s. The readings immediately got better.
But I was still seeing KR on and off. And the 02 readings were a bit lean. So I added an adjustable fuel pressure regulator. And bumped the pressure to 42 psi from 38. My readings are right where I want them now! And no KR! on 91 octain fuel.
As far as I'm concerned, if your hittin the bottle pretty hard. The plugs should be changed every few months. We'll see how the autolites hold up.
Good luck finding your problem.

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Mario,
White 94 Z28
Yeah I got a few mods
Video
Black 87 IROC-Z

 

To my knowledge, its normal to have some false knock due to the spike in cylinder pressure. I get it too, so says my LT1 ScanMaster.

 

Thanks for the info. Kain, how much knock retard are you getting with yours?