This first! ---> :doh: so this has been set up at 8-9 psi. Running 92 pump gas.. is it just a octane problem? timing? I think I have a picture of the map I have in the msd.. Its only this piston. The rest look fine. also at WOT it was in the 10.5 range on the afr gauge..

9# on pump gas? what's the static CR, how much timing?

What's your CR? Fuel distribution problem?

Its a 8-1 motor. timing is a hair over 1* per pound of boost iirc. Its a map in the msd. I did find a chart on BDS's site that says I was probably about 12.5 - 13.1 final compression. Unfortunatly I didnt know until it blew a headgasket. then I noticed the piston.. not even sure how many passes I made with the blown gasket. Wasnt swapping fluids just eating water.. also ring gaps are .025 top and second ring.

forgot to add FP gauge is at 12 at WOT and the AFRs at 10-10.5..

were your ring end gaps setup for your combo?

If the motor still spins over freely (rings not butted) what you have is caused by detonation....which is caused by too much timing, too low of an octane of fuel or oil is getting into the combustion process which is lowering the octane....

You, obviously, have no quench and mid 10's AFR is way too rich....Too rich washes oil off the cylinder walls, which puts heat into the rings, which puts heat into the ring lands, which lets the ring lands move and pinch a ring which lets oil into the combustion process....

The motor needs at least one if not all four of these... quench, better fuel, less timing, cleaned up A/F ratio...

Show us the ends of the top ring when you get it out. Looks like part of it is missing?

.025" seems pretty tight for a turbo motor.

Would like to see what is left of the ends of the top and second rings. More than likely they have been butting at .025 ring gap. Really need to be above .030 IMO.

I personally can't make a judgement on your quench. When you are playing with power adders you can't be lazy on checking plugs. Should have seen this coming. You are seeing this damage on one piston. I suggest you remove all 8. I will bet you have at least one more that is lifting the ring land. Look over in the holes sometimes you can see a mark next to the valve where it has touched the head.

If you are running boost to equal a 13.5:1 compression ratio you are going to have to drastically take timing out. 93 octane is going to be sensitive to detonation.

Just to clear this up you do not have a cooked piston. What happened is you had a rich fuel mixture with too much timing. Your fuel was not getting burned and it basically puddled around the top ring. As it leaked by the top ring it got trapped between 1st and 2nd. This fuel will still light with heat. When it did it kept trying to lift the top ring. After a while the ring land is touching the cylinder head. Note every cycle of this accorance it becomes easier and easier to do. When the ring land hits the cylinder head it pushes it back down some. Before you now it you have broke the ring land out of the piston.

If you run a real tight quench the cylinder head will in a matter of speaking fix the piston. The real way to fix it is to run enough ring gap to not have problems with bad tuneups. I also recomment putting the top ring gap towards the intake manifold. The second ring gap towards the exhaust manifold. When runner power adders you are going to screw up and this allows that fuel to get to the crankcase where it discontinues trying to kill your piston.

Leon

if your fuel gauge is at 12 at full throttle and you were running 9lbs of boost thats a problem. You need to run 6-7lbs base then 1 lb per.
You say your pulling timing at 1 per also but what did it start at? You figure your total timing by what the plug wants....Pump gas sucks for boost is it intercooled or hot air?

your piston looks more broken then melted so i would go with detonation, Detonation will lift the head enough for the gasket to fail and crack the piston.


Last thing, NOTHING replces pulling a plug and looking at it. gauges are OK but not a replacement for pulling plugs.

I burned 2 #3's...both times it was because I forgot to turn on the extra fuel pump...and it went lean. This was only on 6psi of boost. That looks dead like the 2 I burned up...same deal everything else was fine. Just jam another piston in and go!

Leon 441

That was a very good analysis and well explained comment.

I have had burnt pistons like that in a SB motor.No Nos or blower stuff


Same principle apply?? The pistons I have burned looked just like this one on this post

I'll try to give more detail later when I get home from work. But a couple answers. The fp gauge only goes up to 12 and it was pegged. Also the thing was still running when I tore it apart. Timing pre boost was 38* I don't remember exactly what the ramp retard graph was. I need to look it up on the computer in the shop. No signs of the piston touching the head. It is down the hole a touch and I run a .062 copper gasket.

Lots of good info. Looks like I have a lot of learning to do. I guess the rumor was right everyone toasts their first boosted engine.

This whole pump gas thing gets tricky ESPECIALLY w/boost, nos etc. and I wouldn`t even consider pump crap in ANY of those motors...........I don`t even run pump 91 in my lowly 175 cranking motor and never will. Had a conversation w/Jason Pettis about pump junk and even the 10.1.1 stocker motors we built ran race gas................

Not exactly sure what "stockers" they were but guys like Gene Buell and others w/small and big blocks w/limited comp. all ran race gas.......even 9.1.1 motors iirc.