Hi Guys,

No sings of det on top of the pistons. I was running 260whp 1,3bar boost with these stock pistons.
I guess this was their limit overall.

 

When you re-assemble engine add a little more ring gap.

 

Thanks! I will comeback on what the orignal ringgap was on this build. might be interesting.

 

That's really quite impressive. I don't believe I've ever seen that portion of the piston shear off so cleanly.

 

I've had that happen exactly at least twice that I can remember. Both times I can only attribute to power adder with insufficient ring gap. You would think I would have learned to check ring gap after this first time LOL... Once was an older 240sx with a stock ka24e engine that was turboed, second time was a big block chevy on nitrous with hypereutectic pistons. They looked exactly like that as far as I can remember

 

top 0.0216 - 0,55mm
bot 0.0196 - 0,50mm

seems no issue here

 

Yeah that does look like sufficient gap for normal operating temps and sane boost levels. Maybe you did get some detonation. Cast pistons cant take much of that.
However I usually like a little more gap on the bottom ring personally.

 

The factory rods are forged but have a relatively small beam cross section and should be upgraded when going to forced induction. What is not commonly discussed is that the factory cast pistons are an equal failure point. The reason is because most upgrade the pistons when they upgrade the rods. When I did the calcs for the ring end gap I was surprised that .020" (.5mm) was barely enough for the top ring. Although .001" of face and bore wear will increase the end gap by .003". The upper ring runs hotter then the second and they can be equal in gap at ambient temp. My recommendation is .020-.022". Ring butting is not common in NA applications but can be in FI. When they butt, they don't just break pistions. The bore will usually show signs of vertical scoring and faces of the end gap become polished.