| the stock chamber is too shrouded to benefit from the 1mm OS valves .. (low lift suffers) With 88mm pistons you can do a half decent job of deshouding them as you can open the chamber a little more . I would run .5mm unless you do what I did and run 89mm pistons and match port the chambers to 89mm. But you will need custom pistons to bring the compression back up to where you want it .
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