Oddly broken piston

[CatDaddyDrift]

So in my brother in laws RB20DET engine. It started to get a lot of blow by on a 0 mile “fresh rebuild” (according to the person we bought it from)....

It had a few drift days in it, and it still felt as fast as ever but the blow by suddenly got a lot worse. It seemed bad enough that a headgasket might be blown and there was a lot of condensation forming in the catch can.

Pulled off the head and the head gasket didn’t seem great. Probably blown, but it was hard to tell because the head studs definitely weren’t evenly tightened.

Now the tops of the pistons all looked very very good but for the hell of it he tried to do the old WD40 drain test. Fill the cylinder with WD40 and see what happens.

#6 drained in 30 seconds. The rest took 10minutes.

Found this on #6 piston:


The bearings don’t show any pin marks, cloudiness, scuffing. The piston tops are damn near perfectly smooth. There are slight slight needling marks at the quench pad area. Maybe the Squish was too tight.

Very strange. I’ve seen ring lands break but usually you can see heat and buildup leading up to it. This looks like it broke stone cold.

Do Old cast pistons sitting in an engine forever not being used get brittle with age and no heat?

One sudden burst of detonation one time randomly cause this in one single blow?

[rustbucket79]

Drift days. This is nearly WOT sustained (high load/high inlet temperatures/moderate car speed) for quite a run. Very likely that piston detonated in that situation. Forged (pistons) would put up with more, E85 might be a better option. Timing offset table with elevated air inlet temperature/ enrichment.

[JES]

Yes detonation. Agree with Rustbucket

[BLSTIC]

Also a lot of drift cars will have an undersized turbine to try eek out every bit of boost threshold and response. That won't help detonation if that's the case.

[CatDaddyDrift]

3 for 3, I’ll take your word !

Forged pistons are being ordered.

The turbine isn’t small like lots of people run, but we will
Be monitoring egt and iat from now on as well.

Thanks guys!

[modok]

MAYBE it broke the ring land, then melted it back together again ??

[Fusion Works]

Pics of the bearings? I see no hammer marks on top of the pistons, very little black death on the sides of the pistons. Did you find the missing piece?

[CatDaddyDrift]

Fusion,

The missing piece was sitting in its place upon removal it fell apart.

Sorry I don’t have pics of the bearings.

[quickd100]

Detonation! Did that to a couple sets of cast pistons with to much boost and not enough octane.

[stealth]

Not so odd...

see video:
https://youtu.be/AoNNfcfFTdU

[CatDaddyDrift]

Stealth,

That must have been it. He did notice a #6 random misfire and the injector plug had wiggled a touch loose. Un plug, re plug. Misfire went away for good.