[Kerry]

I don't believe in magic,,,,,,,,,,,,,, over the last 30 years i have seen all kinds of piston failures. They were mostly in the 2 stroke world.

Had a 4 stroke boosted motor pull the wrist pin out the bottom of the piston. The boost was coming and going causing what appeared to be a misfire at about 9400 rom and 26 pds boost. The jerking misfiring was just more than the stock cast piston could take. Ran it several times before figuring out what the problem was.

Had another 4 stroke I raised the compression from 8.6 to 11.5 trying to run 16 pds on 93 oct. The timing had to be so low it lost power and I just bull headed kept razing timing till I sized it. That means the piston got so hot that it swelled until it stuck its self to the cylinder walls and scared the side of the piston.
Putting the same motor using e85 allowed the timing to go way back up advanced and made incredible power over the 8.6 comp.
However as boost went up it began to go the other way again and began to loose power.
Not sure where the defining line was but some where of about 25 pds and up and was better at the 8.6 even when going to pure methanol.

Every motor is different of course. This is a 1.8 litter and exhaust piping intake manifold all has a huge impact on how it reacts to boost and compression. I could never ever run this motor at 14.7 afr under any circumstance. it would be weak. cruse I could do 13.1 that was about max and top end liked 12.0 to 11.9. Would make the most power.

I think its kind of hard for deto to bypass all the other parts. piston top spark plug head valves and then have enough force to go to the ring land and break out a small piece. You should see the spark plug on my 2020 silverado when running 87. Not good. as far as knock goes.

I think its a weak piston and cannot stand up to the extra pressure from boost. The ring did not break any other part so it had to bend slightly right their across that small span. If I had kept standing on it Im sure more damage would have occurred.

If the rings butted that hard their would be some evidence of that. Score mark on the bore, ring bent ect. it could butt alot before it broke the ring land in that one tiny spot but no where else. i just dont buy that. If a ring hangs its gonna tare up crap and now!

How hot does a ring have to get before it can grow 14 thousand of an inch. 14 thou think about that for a minute. Ever heat anything and press fit or freeze it. it does not grow no where that much thats alot 14 thouand I think thats a crazy amount to grow with out loosening tension. 2 to 3 is about a press fit

Hell I dont know Im just some hick living in the woods but I been around a while and seen some things.

[95 imp]

Originally Posted by Spaceme1117

Not saying this failure has anything to do with piston to wall clearances. I am aware that stock cast or hypereutectic pistons expand less than forged pistons.

But stock NA engines run tighter piston ring gaps that don't allow much margin when supercharging. Push the boost too much and it will break a piston.

As I read it, the OP is saying his piston ring end gap was 0.014. From that Summit Racing document, they recommend a 0.0080 multiplier times the bore diameter for street supercharged applications to be safe. That means 4.065 x 0.0080 = 0.0325 piston ring gap.

And the OP running 11, 12 psi of boost is a lot for a NA engine.

The chart was General guidelines.

If you take the .0065 multiplier for NA street that would be a .026 gap, which is almost DOUBLE what the OP has.