Piston to cylinder clearance
Senior Member
Joined: Oct 2004
Posts: 4,270
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From: Texas
If you don't have the proper documentation on the pistons & rings you bought, I would advise you contact Supertech and get the proper gap formula and any other information you need from them. My CP pistons came with a spec sheet which specified all this. My top ring was .020, second ring was .022 and oil rings were OEM spec. Clock them exactly as the helms states.
Just to give you an idea, Honda OEM spec is:
Top Compression Ring: .008" - .014"
Second Compression Ring: .016" - .022"
Oil Rings: .008" - .020"
Also when I did mine, the machinist that did my bore and hone file fitted the rings for me, cost was $35 which came out much cheaper than a good ring filer.
Just to give you an idea, Honda OEM spec is:
Top Compression Ring: .008" - .014"
Second Compression Ring: .016" - .022"
Oil Rings: .008" - .020"
Also when I did mine, the machinist that did my bore and hone file fitted the rings for me, cost was $35 which came out much cheaper than a good ring filer.
been there done that
Joined: Jun 2002
Posts: 30,637
Likes: 0
From: 916
um..theyre pistons from KMS at honda-performance.com...i believe the brand is supertech or something like that..theyre 9:1 cr with 84.5mm bore. the only reason im asking is because i talked to a guy who was running about 28psi and he locked up the bottom end...he said it was bc he didnt have enuf clearance under that much boost...i wasnt too sure about that so i figured id ask...it says on my piston specs paper the minimum clearance is .00315"
When you boost in a lean condition, the upper part of the piston expands quickly. Since the ring land area is cut smaller than the tapered skirt below it, the first part of the piston that pushes into the cylinder wall is just below the oil ring. Thus you will see the worst scarring on your piston right under the ring lands where the excess heat is the highest.The more heat that is generated, the harder the piston pushes into the cylinder wall. The uninformed would blame the piston damage on bad piston to wall clearance. Untrue. If that were the problem, the damage would show up at the very bottom of the skirt. What has happened is that you have expanded your piston to the point that it has just ground itself into the cylinder wall.
so as long as you set your clearances to the recommended by the manufacturer and your tune is good, you shouldnt really have any issues. if i recall correctly, supertech pistons have a higher silicone content and dont expand as much as most other pistons, provided everything else is equal.
