I have a 97 502MPI it has 403hrs on it. I hear these motors have head gasket issues. I boat alot so wanted to freshen the motor this winter. Are there any simple or cheap upgrades to squeeze some more power out of this thing. While in the freshening process. One thing i would for sure like to have is a little bigger cam. I know i cant afford to spend a ton of money on a big engine build but i atleast want it to sound better. ALL IDEAS WELCOME. Thanks guys.

What kind of $$$ are you willing to spend on a refresh and upgrades. That's going to be the big determinate of what you can do.

Call Bob Madera at Marine Kinetics for a cam. Your best bet would be better heads (aluminum possibly), bump compression a bit, bigger cam, and good exhaust manifolds with long risers to be able to maximize cam without reversion, and re-tune the ECM. The intake is extremely restrictive on that motor and will be the limiting factor. Should be able to add 100 hp doing the right things that way. Talk to Bob, he knows these motors. Budget will be your biggest factor and determine what if anything you can do.

I was hoping 4k or under on cost. Is that pissing in the wind or what? Thanks for the responses guys. Keep em comin'

Keep an eye out for some good used stainless marine exhaust. Heads will likely be your biggest expense if you go with nrmew aluminum. Can have yours reworked for alot less. I would think that $4000 should be a hell of a start

M3SC Procharger an leave it alone...i have one an i put one on for a friend 4yrs ago motor has lots of trouble free hrs wit pro charger....

I wouldn't touch it with 403 hrs. IMO, its a waste of money, especially without at least doing a leak down test and finding an issue. About the soonest I have ever heard of somebody loosing a head gasket on a 502mpi is 550hrs. Plenty of people have 800+ hours without them ever being taken apart.

I have about 680 hours on my 1997 502 mpi mags which run great and never been apart.

I put over 1,000 hours on my first set of 502's with a valve spring change around 500 hours. Nothing but problems with rebuilts after that.