10secz

Twice since running the ys-trim kinda hard I have pulled plugs that had their gaps closed down to maybe 0.005". The first one was an Autolite 104 from #2, the second time was a Champ RS5C race plug from #8. There was no sign of contact in either case. And yes, I'm quite sure I didn't drop them either before or after running them. Initial gap was 0.035" in both cases.

Mike Blackstone (the guy that did the engine) said he has never seen a case where detonation had closed a plug gap. His only suggestion was to look into side gap plugs. Do you guys have any ideas about this?

znines

I run a NGK 5724-8 (TR8) gapped at .025 and have never experienced closing gap.I do change plugs after a couple passes and notice the gap opening up. If the plugs open to .030-.035 they will blow out with 23lbs. boost

Lonnie Pavtis

Detonation will often close the gaps. Check your tune, you may be on the ragged edge of engine damage. Do you see any pepper like specks on them?

10secz

This is where it gets weird - I checked the plugs with a magnifying glass and didn't see any specks, and the car is running rich at WOT, 11.0-11.5 AFR according to my dual widebands. Max timing is set to 28*, although the DataMaster logs show 32*, meaning that I have (or maybe don't have) the mysterious extra 4*. Next time I'll back off to 26*.

cmotorsports.com

One word. Detonation. Even if you can't hear it, it's there. That's what will cause the spark plug gap to close 99% of the time on an FI motor. Happens quite a bit actually, even on naturally aspirated engines. Forced Induction engines are particualarly prone to this, though. My car used to do it quite a bit, even though there was no knock recorded during data logs. To make sure it was detonation doing it though, we ran 106 octane for a couple of weeks. No closed gaps at all. Only thing it could be was detonation. Hope this helps.


Seth

Josh-'04 GTO

Whoa! I've been following your buildup on your website, and am surprised you are having detonation problems given the amount of work you put into the fueling system. Now that you are running copper head gaskets, let's hope you don't scrap the shortblock!

airflowdevelop

LJ,
It is almost certainly detonation, It can also be caused by a slow flame front "softening" up the plug, although this is not normally a problem on small bore motors. On our 4.300-4.500 bore motors this is pretty common, but hard to believe on a 4" motor w/ an effecient chamber.


Dennis

Jason Short

LJ, I assume you are still using LT1 Edit to tune your car.....I would back the timing down some. For some reason, I have noticed on my own car that the actual timing is ~3 degrees more than what LT1 Edit *says* it is supposed to be.

Sounds like it is right on the verge of detonation.

Jason

BigRick

One word, Detonation. At SBSO I had some fuel problems and detonated on the dope. It closed the gaps complety on half my plugs. This is where it get's interesting. I though I had blown my motor when I got back to Houston and made a motor pass after all that. I determined I had a dead cylinder and thought it was from melting a slug. Well what happened was the rail for the shaft rockers bent. The heli coil was pulled out of the heads on the #7 cylinder! I thought damn my triple valve springs with 320lbs seat pressure and 1000+ open caused the problem. The guy at T&D said no way the springs could have bent the rail. The only thing that could was detonation. Detonation has over 35,000 lbs per sq inch!!! $200 later with a new rail I was on my way to Bowling Green.