I am not a firm believer that the $ spent on expensive large valve heads is worth the $. Then again I feel the same way about an MPX over an S trip :O)~
In both cases it's how you use it that matters. Phil's car went from 400rwhp to 325rwhp going from the MPX to an S-port. The S-port has 10% OD and the MPX had 20, but that doesn't account for 75rwhp. Nothing else changed on the car.
For people wanting 300rwhp you can get away with just about anything. You can port stock heads to the max and keep your stock valves, or you can upgrade to a larger valve and skip the porting and get the same results. That's just an example. Bigger valves gives you new, better quality parts, and costs less than spending all that time porting the stock valve heads. I've got more than one mid 12sec car out there with stock heads with just bigger valves and matching cam. What people miss a lot of times is that it's not what is done to the heads so much as it is how the combination is matched both to the cam and blower and also how you drive and what your power level expectations are.
SSM heads are limited just as Dave Clark's Steigemier heads are due to a couple of reasons - first they overport the exhaust side which actually results in lower flow #'s. This is a flaw in 99% of all the heads that come through my hands after being ported by other guys. Once you take out too much material there is no way to fix it short of welding and by the time you've already bought what you thought were ported heads, welding them is kind of like starting over and completely unnecessary if they were ported right in the first place.
I have avoided most flow number discussions frankly just because almost everyone seems to lie about numbers. I don't care that much about the hard #'s if the heads are done right in the first place, but I've had the chance to flow just about every imaginable SC cylinder head out there on the same flow bench using the exact same templates on all of them and so whether or not anyone believes my statements, I know how the different heads compare to each other. I know what works, and what just looks cool. I also know when people are exaggerating.
It
does make a difference if you have highly ported, full on cylinder heads as opposed to something that is just "decent". No offense to Dave, but when you struggle to make 400rwhp when other seemingly similar builds are making 450+ then you have to question the cylinder heads. I know what they flow, and I see the results. You don't have to believe in science for it to be real. I know the science behind cylinder head flow #'s and I've seen the results over and over.
That being said, for 300-350rwhp, most any non-butchered cylinder head will do. Phil's car made 350rwhp with completely unported heads (but with appropriate cam and properly set up big valves). That's easy and can be accomplished with just about any cylinder head out there unless it's been totally ruined.
And no, this isn't a sales pitch. I am not trying to sell heads I'm just trying to inform. I have more work than I can do, for which I extend many thanks to the people of this community who continue to support my efforts.