When you are going with forced induction, a great flowing head is not as important as a naturally aspirated engine is.
Having a bad flowing cyl head on a naturally aspirated engine has a big impact on how the engine is going to make power.(it will make bad/low power because the the bad flowing cyl head.
On a N/A engine it is hugely dependant upon a great flowing/high port velosity cylinder head to get some good/great HP & torque numbers.
When naturally aspirated,,, If you open up the port windows too big on our siamesed cyl heads, the port velosity will drop too much & in return, you will have a doggy, no low end low torque engine.
Being said that, when you are forcing air/fuel into your engine, you need to see where the ports narrow down the most & you would benefit by making these areas wider/taller up to a point, (don't go overboard with the porting)
Also, if your valves are only so big/small, they can only allow a certain amount of air/fuel through the valve throat areas (another bottle neck)
So the minimun head work I would do is go w/oversized valves intake & exhaust.
Open up the bottle neck areas/port windows, basically anywhere the intake port gets smaller, open those areas up.
Profile the intake boss on the cyl head into a wing shape profile, but not so far where you are going to get into the head bolt hole.
Machine & install screw in studs, because you are going with a roller camshaft, or bare minimun pin the studs.Doing this type of basic work on your cyl head will pay off & will not cost an arm & a leg, or so to speak.
If you do not do @ least these type of basic mods, it will be harder to make 400 HP.
My 262 V-6 only made 386 HP & was pushing 21 psi though it.
560 ft lbs though.
Rating is from R.W.H.P.
I would be more concerned with the torque output & not focus too much on the HP.
With having a siamesed cast iron cyl head, they are not going to make a lot of HP as compared to torque.
Just saying, it is not going to produce a lot of HP like a 4200 engine does, & the main reason is because the 4200 engines cyl head, it flows great & is a much better design.
Hope this helps.
MBHD
