1985 Monte Carlo SS known as Barney

[mfain]

Lance,

Do you see any signs of detonation?

Pappy

[SSLance]

Originally Posted by mfain

Lance,

Do you see any signs of detonation?

Pappy

A lot on #4, the one that cracked and burned and just a couple small pits on #1. Tops of all the rest of the pistons look great, including #8 with broken ring land.

[mfain]

Originally Posted by SSLance

A lot on #4, the one that cracked and burned and just a couple small pits on #1. Tops of all the rest of the pistons look great, including #8 with broken ring land.

Might want to investigate the source of the detonation - usually an octane, timing, or AFR problem. Cast pistons tend to give up early (broken ring lands or cracks at the wrist pin), but even good forged pistons don't like detonation. Were you running an AFR gage or monitoring EGTs? With a nominal compression ratio, octane should not have been a problem, barring excessive timing advance. Sounds like there might have been something in the tune at some point that was causing problems - just my opinion.

Pappy

[SSLance]

I was not data logging at the time, but I have plenty of WOT logs showing the tune performing as desired.

I'm still leaning more toward something happening in that cylinder that raised compression or lowered octane enough to cause the melting of the edge of the piston. There were several mechanical failures there and all of the rest of the cylinders were fine.

We may have been close to the edge and a minor variance put it over, not discounting that...but if it truly was only tune related, it would have shown more damage across the board and most likely would have happened earlier.

It had been pushing antifreeze out recovery tank for two events prior, indicating the start of the real problem. The burnt piston is more of a result of that problem than the tune.

But yes, I probably will back it back away from the edge next go ahead.

[Tinker]

Too bad you had to tear it apart again Lance, but addressing the possible shortcomings will continue to make your engine more bulletproof. I enjoy following your journey because except for a minor setback such as this your car is a contender amongst much higher dollar builds out there. Keep it up and let us all learn and enjoy with you as you go.

[CamaroAJ]

Just throwing this out there, what were the ring gaps set to?

[SSLance]

Originally Posted by CamaroAJ

Just throwing this out there, what were the ring gaps set to?

That is on my list of things to check.