What happened here

[R/Tony]

Hey guys I need a litle help here, my setup is a 2.5CB with std forged pistons, almost all of the bottom is forged, 8v ported head, TBI roller cam, Holset turbo, Big front intercooler, Megasquirt and some other goodies....

Well I hope you can tell me what is your first thought when you look at this piston:

This is the 4th piston still inside of the block:


Its a forged JE piston











This Picture was taken one week before the damage:


I guess it was too much timing and also could be some heat, but I will need more thoughts please.

Thanks.

[tryingbe]

Ran lean.

I'd get a new block.

[turbokid]

Shit son... Even forged...
Ya prolly ran lean would be my bet.

[8valveprick]

holy detonation. looks like my stock 2.5 piston did after 27psi on pump

[phantomrt]

I disagree with everyone. What was the piston --> cylinder wall clearance set at?

[speeduphoria]

you can clearly tell that there was detonation from the pitting on the pistons. I bet the head has similar marks. Also if the ring gaps were tight that could have been a secondary issue

[jim34]

Yep detonation attacked the weakest part of the piston must have went lean or overheated, How much boost were you running and what octane ?

[moparzrule]

Had the exact same thing happen to me, that is a lean condition right there. My FPR turned out to be faulty, staying at base pressure not adding for boost.
What was your A/F ratio?

The piston to wall clearance *may* have had an affect if it was set too tight, but being too tight would not make that happen on it's own. There was definite detonation, and when the top breaks off like that it's a lean condition detonation.

[Sittn86]

Quote:

Originally Posted by R/Tony Its a forged JE piston

You mean was?

[lancerman23]

i agree way to much detonation! what kind of guages you running? 3 bar map? as you can see i is definalty worth the money to get a GOOD A/F RATIO GUAGE... i use the AEM's wideband UEGO guage and i've never had a problem with it.

[crazymadbastard]

Too much boost, not enough octane and gas. PING PING PING!
Ouch!
Same happened to me went to 18-19psi with a cal that did not know wtf was happening above 15psi. Live and learn- did you have an eye on egts? I was running maybe 11s on the wb and 1600s egts- funny thing is that the hose popped off the wastegate can and I hit 29psi with no damage a few weeks before- but the air was much cooler then. Time for a new block and piston.

[R/Tony]

Quote:

Originally Posted by moparzrule Had the exact same thing happen to me, that is a lean condition right there. My FPR turned out to be faulty, staying at base pressure not adding for boost. What was your A/F ratio? The piston to wall clearance *may* have had an affect if it was set too tight, but being too tight would not make that happen on it's own. There was definite detonation, and when the top breaks off like that it's a lean condition detonation.

Well I dont think it was lean condition... check this log:

Quote:

Originally Posted by jim34 Yep detonation attacked the weakest part of the piston must have went lean or overheated, How much boost were you running and what octane ?

It was running rich (10:1 AFR in a LC-1) and it was not hot Im sure... the only reason could be detonation, I was using premium gas with toluene and xylene, with about 20psi of boost.

Quote:

Originally Posted by phantomrt I disagree with everyone. What was the piston --> cylinder wall clearance set at?

Yeah... It was way too open ! it was something like .010 or .012 dont recall the exact value at this time.

[R/Tony]

Do I need to change the block ?

I have already bought the pistons, but also the block ? and why ?

[mopartech]

heat. heat broke that piston. did you make sure you bled the cooling system ???

if not then thats detonation. i dont care if it shows it running rich.

[Gutfeeling]

If only that piston did that, then I'd say it was a wiring/injector problem with a possible ring gap issue.
Cylinder goes lean, heat expands the ring, piston fatigues and crack goes your JE.

If all are experiencing that issue, then check to make sure the logging software is reading right. Also, iirc while using toluene and xylene I think you need to run richer of an afr.