The guys at the machine shop told me you cant go real deep on gt-40's cuz of water passages, if i were you i would just clean up the intake side, and cut out a good amount on the exhaust and polish smooth).
my intake was hogged out, carved on the upper inlet, and opened up the lower pretty good, on the lower part of the runners they made a swirl rough polish for turbulence.
I would recomend a 3 angle valve job also.
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