Flycutting of the pistons all depends on your total lift, rocker ratio and duration of cam. Remember that big lift cams don't always mean big power, the entire combination has to work together.
Check out TFS' site at
www.trickflow.com for some good technical information.
FWIW, on my old setup, I had used a .480/.480 (w/1.6's) 220/226 with 115 lobe separation with no issues whatsoever. My new engine has custom TFS TW pistons (Probe Industries Sportsman Race Series) so that I'm safe to nearly .650" - way more than I'll ever go.
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