without sitting here and writing an essay about it the only answer i could give is use a .82 or larger.
the reason i say that is why would you make the engine breathe better with largish cams and a big turbo only to restrict exhaust flow by using a small exhaust housing like a .63?
if your chasing 400rwkw i wouldn't use anything smaller than a .82 and would probly end up choosing a 1.06 just to make sure it can get the topend numbers you require.
cheers
linden
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