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Evo 8 2L Build Piston Ring End Gaps & PTW

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Hi guys,

I'm building my 4G63 engine in my Evo 8 and I am aiming for a 450kw (600hp) capable engine.

I'll be sticking to the standard stroke and standard length conrods.

I have ordered Wiseco 2L 9:1 CR 85.5mm pistons (K626M855AP).

Wiseco recommends:

Top ring = 0.0168" (Bore x 0.0050)

Bottom Ring = 0.0185" (Bore x 0.0055)

PTW = 0.0035"

From what I've read online. Everyone seems to be running slightly looser clearances. Eg Top ring = 0.02", Bottom ring = 0.022, PTW = 0.004".

Should I follow the manufacturers recommendation or run slightly looser clearances for the power I'm chasing?


Hi Nathan,

Those ring gap recommendations sound accurate for a piston of that size, but perhaps a hair on the tight side. Tighter is better to a point (less blow by etc) but too tight can be catastrophic, when a piston experiences too much heat (thermal expansion) the ring gap can close and bad things happen.

On a turbo engine the piston temps can raise quite dramatically, they require extra fuelling not just to compensate for extra air coming in but keeping temperatures stable as well. If your running E85 fuel your piston temps can be quite a bit lower than on 98 and less prone to heat soak, in which case the tighter gaps may be acceptable. But 30psi+ on 98 pump gas may need a little extra room to expand as things can get very hot very quick.

I hope that info helps in some way.

Agreed - a couple of thou" too big and you may lose a tiny bit of potential power - a couple of thou" too small and you lose an engine... the greater the power you expect to make, the more heat in the engine and the greater the ring expansion... and if you run it a bit lean, then it is even worse.

You pay the bills, you make the call.

I would be more than happy with those ring clearances for the power level you're aiming for.