I am wanting to overhaul my engine its a 502 mag mpi. going to make a 509 go with promaxx 317 head not looking to get into a debate on this head or that head. My main question is what cam would be a good cam? really would like to get to mid 650hp. boat is 7200 lbs. I plan on upgrading the manifold to a holley and going with holley efi. Thanks in advance

Don't know what ECM you have but Eddie young programed my MEFI 3 to get 530hp
MEFI is easier to tune and I'm sure there are some here with the correct bin files. I have the one for mine

Not going to make 650hp out of a N/A 509ci without some crazy high lift cam and spinning it to 6000rpms+

Consider getting a new crank and making it a 540.

Also, what out drive do you have?

Did you plan on upgrading your oil cooler?

Thanks Griff, did think about a 540 but not sure yet.

I'd be more concerned at building torque then horsepower with a 7200lb boat. You'd have to spin it 6000+ and more compression than I'd be comfortable with. I'd try to keep it to 5600 and as much torque as possible. At least you're starting with good heads.

This is the cam I ran in a 548 with iron 088 heads I used to have. I also had a really heavy boat and the torque definitely was a plus. I am currently running the comp 525efi in my current motor and happy with that cam.

On promax web site they say .600 max lift for 317 head. Does that not apply if you use different springs?

That's if they are assembled. Buy bare and build to your specs.
My SBF 302 heads came with PAC springs I believe. My head guy asked them to send an "assembled" kit and he would assemble them.

its part of the equation,valve stem length and and spring pocket depths will then let you pick a spring for higher lifts.