What do you think is the cause of this piston damage?.

Diamond 2618 forged pistons. NA application. Tuned with 12.8 AFR.

Note; Only pistons # 5 and 7 got damaged. Others were fine. Spark plugs tips were broken and melted.

 

Looks like the comp. ring snapped the top of the piston forget what its called.. It could be detonation

 

Spark plugs. All three are on driver side.

 

Looks like the ring expanded to much

 

It was running fine for 6-months with same tune. I doubt it is detonation.

I am suspecting a failed injectors on those two damaged pistons or fuel pump.

I am running stock fuel pump and 42# FMS injectors (green top).

 

It looks like they were firing. Pre-ignition??

 

they overheated for some reason, might be fuel injectors screens are dirty or if the timing ignition setting are a little off same thing could happen. Thats why GM's stock tune is rich so this can't happen too easily. You realize at WOT this can happen in an instant, every cylinder is different. Some run much colder than others.

If your tune is on the edge of being lean or too much timing, Its asking for this kind of thing. Even fuel flow etc can cause this if you are always on the edge with the tune.

 

Detonation and then some damage from the pieces going from cylinder to cylinder through the manifold. Those must be Lunati or something made by Wiseco because no regular Wisecos look like that piston?

 

Is it just me, or does the #7 piston look quite a bit smaller than the bore?

 

Well, if it is detonation, my tuner is confident it's not the tune.

Could it be failed injectors causing detonation. This is what my tuner is telling

I wasn't driving when it happened. It was a friend driving it.

 

those cylinders are also the last to get fuel. when was your last fuel filter change and check for debris in the fuel rails.

 

Looks like the cylinders got a lean air/fuel mixture and drove the combustion temps sky high as witnessed by the obvious melting of the electrodes and pistons. Detonation came in as a result and broke the top of the piston above the top ring. As stated by others, injectors, fuel pressure, etc would be the obvious places to look, if the tune was verified. Any way to verify injector pulse in the computer history?

 

Correction: Diamond 2618 forged pistons.

 

I was trying to determine if it may be a shadow, but it looks like there is excessive clearance there.

OP: My guess is that the fuel pump is going south on you. My tune was fine for a while, then I started having to add fuel to the tune every couple months. The stock pump was replaced with a racetronix and even the original tune was way rich. I highly recommend you upgrade the fuel pump before running another engine in the car.

 

It looks fine at 6 o'clock, but at 12 o'clock there is a lot or clearance. .080"+ it looks like.

 

No excessive clearance, it's just a shadow.

I agree with fuel pump and I have Holly 255 lph fuel pump ready to install with rebuild. Will check the injectors, too, and retune the PCM.

 

I'm not trying to stir trouble....but NOWAY you do that kind of damage without ALOT of DETONATION NOISE as the cylinders overheat from constant WOT.

I had the same mess from a "FRIEND" driving my car. took number 7 piston out, fuel filter was a little dirty and he ran it WOT too long and BAM!

Good luck, change your pistons, get a new tuner, and move on........

 

your AFR is 12.8, whats your compression?

 

CR is around 10.7.

 

i'm leanin with these guys and sayin check your fuel pump to see if it's goin out. you CR is fine IMO you run pump gas (premium)?