The heads will flow plenty for his application.Any upgrades you can do to the L31 you can do to the 4.3.For the cam it would be better to get a custom grind for his application.they dont charge much than ordering an off the shelf one. I say 350whp is the limit for stock internals in that application due to the pistons. well good luck as im in the proccess of duing the same thing using sy/ty manifolds.

 

well we are going to use stock crank and forged rods and pistons. he wants 500whp out of it so we will see. how it does. we will be using meth, 60lb deka injectors, marine intake, eagle rods, forged pistons, cam&springs, and a mpt70 with a .68 a/r turbine housing. maybe long tubes wraped from heads all the way to the turbo. this is what we have come up with so far.

 

Its possible with that setup.If hes going that high in hp then it would not be a bad idea to get the heads ported or get them extrude & Honed like i did mine.To me this is the best way to get everything smoothed out for a boosted application.Also might want to try and install some bigger valves like 2.00" I 1.55" E or even 2.02 !.60. I would invest in some incolnel valves to be able to handle the heat and pressures.

 

Either hot rod or car craft did a 4.3 a few years ago. They had a centrifical blower, carb, different intake, ported heads, gm performance cam? and i think stock bottom end. I believe they hit 500 hp on race fuel before it puked a head gasket or something.