Just a consideration, but with such a large TB as a 65mm, I think you'd really kill off the bottom end of the motor. This may or may not be a concern, depending on your application, but 65mm's isn't going to generate as much velocity at the lower rpms as the smaller TB. I don't have enough experience with how TB size interacts with IMRC and the primaries vs. secondaries, perhaps it wouldn't be as bad as I think. I know on my 3.4 liter pushrod Grand Am, stock is 56mm, we have a 62mm avalible which helps quite a bit, but going beyond that is really detrimental for the bottom end, you just can't generate velocity in the intake system. Like I said though, this is just theory for me thus far on the Duratech, I don't know enough about how TB size interacts with multiple length runners.
