Well Today I swapped the heads on my step dads 68 Corvette for lower compression. Its got a 1970 LT1 and its been smoking out the left side on hard acceleration while pinging. So I figured lower compression heads would work and what do you know, pull off the old heads and piston #8 has a curved crack at the top in the shape of the casting edges on the underside. I figured that was why it was smoking on that side, but after cleaning them all every piston 1-8 had the same shaped crack! Amazing it didn't blow up but that would be weird for them all to crack. Anyway the other heads are on now with the possibly cracked pistons and well see if it still smokes or if it blows up. Anyone have any info or a similar experience? I'll post the part number of the pistons tomorrow but they're the domed GM LT1 high compression's. The piston tops look exactly like these only I'm pretty sure the part number was different:

 

First real "LT-1" (note the hyphen) post I've ever seen here in all these years.

The "LT1" (note - no hyphen) really only covers the Gen 2 SBC LT1 that was used in the 92-96 Corvettes, the 93-97 F-Bodys, and 94-96 B-Bodys (Caprice/SS/Roadmaster/Fleetwood).

I'll leave the post here, to see if someone can help you. If not, I'll move it to "Advanced Tech"..... lot of old farts over there that may have some experience with those pistons

 

All I can tell you about that is that those engines were really high performance for the day and they needed the best gasoline available to not detonate. A lot of those engines, like the hemis didn't really have the best chamber design and they were on the edge of detonation how they were tuned. My buddy sold his recently, and he had to put race gas in it to keep it from pinging on hard accelleration. So it's my guess, that if you have cracked ring lands or whatever, that some inferior gas found its way into your car and the timing was too much for it.

 

The new heads and screwdriver tuning tuned out the pinging and theres no more smoking on hard acceleration. Runs great now. Those heads were way to high compression for todays gas.
Me very happy