So i got a 1990 5.0 HO. Mustang GT.i just got some new aluminum GT40 heads. I was wondering if i should put a better camshaft or what ratio rollor rockers i should use to gain most hp but still be smog legal in cali.
I have no experience with California emissions but I can tell you its a bit of a Pandora's box with these things. Change the heads then it's time for an intake, then injectors and camshaft, fuel pump, throttle body and Maf, and that goes for just about anything on these cars.
I read up a little on those heads, I didn't see a carb (California air research board?) certification but it does have the air tubes so the emissions will hook up, they do recomended that you use a gt40 type intake, explorer/cobra, and like joe said above, it snow balls from there but in a good way, I would gather the parts to take advantage of the heads and install all at once, just make sure the parts you use will pass cali emissions.
The thing that most over look when building horsepower are the brakes and suspension, are they up to handling the new power?