Thread: I thought i did it right, still have KR

02 Grand Prix GTP, mods are as follows
3.4 pulley
ported supercharger
ported TB
fenderwell intake
speed daddy headers
3" ZZP catback
180 stat
Overkill PCM tune
Autolite 104s gapped at .052"

Originally i was still using 605's or something and had so much knock there were misfires, so i put in the 104s and it brought it down to 4-5 degrees of KR at WOT under full load. At the moment I have access to a whole slew of very expensive and awesome tools so now is the time to play. We hooked up the ignition scope to the car today and went for a joy ride and got some interesting data. On a WOT run through a couple gears the firing voltage went waaayyy down, and the spark burn time went as low as .5-.6 ms across the board. According to my instructor burn time should be around 1.2-1.5ms, and go no lower than .8ms, and this means I have too much resistance in the secondary ignition. Since it is fine at idle that means it has to be a variable resistance, i.e. compression, fuel, heat, etc. at full boost. We're going to stick a bore scope in it tomorrow to check for any damage, but if that fails to turn up anything...well i dunno. I have the same mods as so many others I've read about but I still get KR. Should I drop ANOTHER heat range to 103s? Or maybe its going lean somehow? My teachers are pretty smart guys but mainly in the stock category, so if any of you tuner/mod gurus could help me finger this out I'd be much appreciative.

Yeah...so we stuck the bore scope in it and cylinder 3's piston is fubarred. It's got detonation damage, pitting, and from the looks of it a huge chunk is about to come off. It's probably my fault for driving around without a way to check knock after I started modding. I think I'm just gonna sell it and try to find another trans am to put my lt1 in. Lesson learned.

Originally Posted by Z34Phoenix

i have heard some people even need rockers to run a 3.4 is that correct? it sounds like he has enough supporting mods to me though.

I needed rockers to run a 3.4 with decent timing at AFR that wasnt in the 10's, So id say so.

Originally Posted by bluegtp91

Meh, this is where the "scan because every car is different" comes into play.

Plenty of locals here are running knock free on just a 3.4" with headers as no other mods...well and intake/180*/plugs/wires...but those really don't do much...and a good tune.

Oh i ran fine and knock free on a 3.4 on just headers, intake, and AL104's -- But i also had to run mid 10's for AFR.

I was thinking about it today, and I might just go ahead and be a super cheap bastard and replace ONE piston. If nothing else, just to see if it works. Pull one head off, take out #3, swap the old rings onto the new piston and put it back in. I can already hear the cries of "you might as well..." but I don't want to. It's pretty fancy for a FWD grocery getter, but a full bottom end swap? A rebuild? I know if I were to take this thing alll the way apart I'd find enough wrong with it that I'd be replacing parts or paying a machine shop for work or any number of things. Dont care enough, I'd rather sell it to the next guy. But if I can put in a 50 dollar piston and only have to buy a couple gaskets? I'm down.