Until you run out of cylinder head. You ain’t making power out of cylinder head.
A W2 struggles to feed 340 inches at 8500. And that’s fully ported. That’s a W2.
A W5, like the Indy 360 makes 8500 on 340 inches a bit easier.
I’m taking about making power up there.
I’m saying on the dyno and at the track, if you are running 400 inches and your rockers are in line you don’t have enough cylinder head/induction to make any power above 6500.
Period.
You can can the **** out of it, but you’ll kill power coming off brake or clutch. It will be horrible in the gear changes and the more gears you have the more it hurts.
To argue that these engines aren’t under headed is absolutely refusing to look at and understand what it takes to make power at higher rpm.
If the OP wants to help himself, he can find a 3.79 stroke.
He can add 500 rpm up top with the same cam timing and it will beat the brakes off a 4 inch engine.