So 500 fwhp or rwhp because you are not going to get either one with a NA 302 without dropping some major coin on it. There are plenty of motors out there making good hp with 9:1 to 11:1 compression ratios. I will say that the cam is the brains of the motor and you typically select the cam based on what you are trying to do with a specific cubic inch motor. From there you select heads and intake and build the motor around that.
So can we assume this is on a stock short block minus the X cam? Assume the headers are 1-1/2" primary into a 2-1/2" fire cone? Is the exhaust system 2-1/2"? What is your shift point in rpm? Can we assume you have a bigger than stock fuel pump? More questions are what size injectors, what MAF, and do you have a CAI? Another question that will directly affect compression ratio is what head gasket did you use? They have different thicknesses so it will affect it and may not be a huge amount but when looking for a little more power NA it counts.
What I am trying to drive home here is you are asking if the heads are the issue when we do not know
about your car, setup, tune, etc. The more info you provide the more feedback we can give.
With a stock bottom end those heads are going to get you about a 9:1 compression ratio which is stock. If you can mill them (I do not know the deck thickness but maybe you can call them and see if they can be milled and if so how much) that will provide the most gain. Realize that when you mill them you may end up needing to mill your lower intake to get things to line up. I had to do this with my Cobra lower to match the heads on that motor.
There are plenty of motors out there making good hp with 9:1 to 11:1 compression ratios. I will say that the cam is the brains of the motor and you typically select the cam based on what you are trying to do with a specific cubic inch motor. From there you select heads and intake and build the motor around that.
A quick piece of advice is to get ahold of TMoss over on the Corral (
[email protected]) and have him port that Cobra intake as that is a lot of your restriction. Tom ported my old Cobra intake about 15 years ago and it made a huge difference. His son Matt is now doing the porting and from what I have heard he has taken it to the next level. I believe they can port heads as well so you may want to talk to him about that if you want to keep those heads. I will say that he needs to know just about everything we have asked you to provide information wise on the car so he knows how far to take the porting on the intake. The intake needs to match the heads flow wise so things work together and to not create choke points or lazy flow.