Piston 2&3 Cracked ringlands
#5
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
#8
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.
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mekaw
Engine Performance
10
04-29-2010 11:03 PM