I have used these heads on several engines and my dynojet numbers were much like a previous poster..
On a 383 GM and a 347 Ford it was difficult to exceed 400 HP. But all made very VERY good torque.
I have to agree these are not the best heads to hit the market.
They are however, super affordable..
I am in the automotive machine business , complete heads with roller springs and 2.05" intake and 1.60" exhaust valves are around $800.00...
The biggest flow problem I have with these heads is that they use a cutter before the seats are installed and just plunge it down into the bowl leaving a huge ridge.. Making porting them a new adventure.
If you are handy at all, a few hours on these heads really opens them up..
It does take some handywork to get any sort of a match on the intake ports..
I just built a 383 GM ..
Using a pair of hand ported ProComp heads.
An ******Comp cam.
A modifide RPM Vortec intake..
Flat top pistons.. < some pinging issues, that a more aggresive cam will hopefully overcome>
Not unusual with some Comp cams with the fast closing intake lobes..
Balanced, blueprinted. line honed and decked .005 only to equalize the deck height..
Made over 430 Hp on the dynojet.. It has enough torque to pull a bridge off it's foundation. I don't think this is shabby for a budget street motor.
Take it for what it is worth,,