I put heads & a cam on my car a couple weeks ago, and I've been working on tuning it for the last two weeks. I'd log my AutoTap runs at WOT, watch my O2's, knock retard, MAF, MAP, fuel cell, LTRIMS... All the stuff I've tuned with before. Piece of cake. I was a little surprised that my car, which WAS showing knock in fuel cell 12 (until I got rid of it) had NEVER shown any knock at WOT... I bumped up the timing 7 degrees, to 29 total at high RPM/high MAP... still no KR. O2's kept reading slightly rich at 890-910, so I kept leaning the car out at high RPM's in search of that last little bit of power. Eventually, my PE table was actually a DOWNWARD slope, but the O2's kept reading 890-905. No KR showing, so I thought life was good.

Then I put the car on the dyno at Camaro Superfest this past weekend. Right away Eric said the car was knocking like crazy, and he wouldn't take it up past 5500 RPM. I was in the car with him on the dyno, with A-Tap hooked up, and I showed him that there was no knock retard kicking in. He replied that whether A-Tap was showing it or not, he could HEAR the knock very obviously. Then he showed me the A/F graph... 12.2 to 1 at 3250 RPM, then it leaned out to almost 13.5 to 1 at 4750 RPM!!!

He let me bump up the power enrichment table to approximately stock while the car was sitting on the dyno, and we ran it again. This time it was a little rich at points, dipping to 10.8 to 1 at 5500 RPM. But no more knock, and I picked up 10 RWHP above 4800 RPM.

I still have some tuning to do... Need to get that A/F just a little leaner... But I'll do my tuning on a dyno from now on, thanks!

The moral: You can't always trust your KR readings and your O2's... (I may just need new O2's, as these have nearly 40,000 miles on them. But I wouldn't have known that since I haven't been getting any SES lights.) Just thought I'd pass on my experiences...

 

Excuse my ignorance, but your saying that 13.5afr gave you knock? Thats hard for me to understand since the computer is trying to maintain 14.7, and peak NA power is at 13.1-13.3afr. Maybe thats the difference in loads too, cause I like being able to WB on the street/highway, on Dyno showed 12.5afr and on street a day later no changes other than weather and I showed 12.8 on a WB. Interesting.

 

The computer is only trying to get 14.7 at idle and cruise, not a WOT. WOT you want a lot richer say 12.5 (or richer) on a dyno. If you are logging more than one or two parameters at a time with autotap you can and will miss a lot of data. You will probably be .5 afr leaner on the road compared to the dyno.

Gary

 

Thats what I was saying basically, w/out thinking of afr on the dyno, then remembered I had a .3 difference leaner on the street when I wideband from the Dyno. I still think that 13.8 or even 14:1 isnt lean enough to get that severe of detontation, maybe a combo of low octane, and too much timing but not just that afr, doesnt add up.
12.5 on Dyno is what I try for when setting up N2O, gives about 12.8 on street, and with NX jets which are a hair rich anyway you achieve a real world of 12.5 on spray.

I think if you get the spark, and octane up, you should be bale to lean it out to a 12.8 on dyno and see more than you are now w/out KR, but every engine cobo is different.

Good-luck.