Ring end Gaps

[Belgian1979]

Looks like a good candidate for TBC.
(and maybe abradable skirt coated forged pistons, to get strength without noise)

Tender butt care ??

[MadBill]

We do love our acronyms, don't we? Thermal Barrier Coating

[Cougar5.0]

I'm fairly certain it wasn't detonation, I didn't note any of the tell-tale signs and others didn't see signs of it when I posted the pictures back when it happened. I pushed the thing over the threshold by adding a KB blower (non-intercooled, ~6-8 psi) to a short block not built for boost. Ring gap was insufficient (not sure what gap was, I didn't fit the rings/pistons), but it was built as a ~9:1 N/A application with the KB pistons pictured. I may have rotated the rings to the broken area to facilitate taking photos of the ends.

The ends of the rings had polished areas which seemed to imply that they were butting (tough to see, but differences in reflectivity imply butting):

Butted_ring.jpg

Other pistons had cracks in the same area (which is definitely weak where the valve relief gets close to ring groove)...

KB_crack.jpg

Looks like it is heat induced/expansion cracking. Any signs the pistons were scuffing ?

I dunno, it's tough to take a photo that shows much, and this piston was also bounced about as it digested and spit out part of the top of the piston out the exhaust. Was after a little goose on the highway that this happened, I drove the car for a bit before tearing it apart. Also, it's been sitting on a shelf for years after sitting in the garage for a while.

2017-08-22 13.49.01.jpg

[Belgian1979]

We do love our acronyms, don't we? Thermal Barrier Coating

ok, thanks, learned something new.

I think you might be right. Although I would have expected scuff marks on the top ring land if it was heat induced.

[pamotorman]

one of my customers raced a BBC dirt modified and had to wire the dip stick in so it would not blow out because of the blow by. I told him the engine needed freshened and he said "why we are still winning"

[Belgian1979]

one of my customers raced a BBC dirt modified and had to wire the dip stick in so it would not blow out because of the blow by. I told him the engine needed freshened and he said "why we are still winning"

Probably the pressure inside the crankcase created some upward pressure during compression and expansion stroke negating the negative friction forces, which gave him extra horsepower

[BOSS 429]

the 2nd ring gap should always be larger then no1