hello fellow boaters,how can i "bolt on" more horsepower to my stock merc 502 mag (1997 model).? already thinking of relatively inexpensive gil exhuast-any thoughts?what else for quick add-ons?trying to acheive around 450-475 hp range without serious modification.thank you:

Exhaust might give you 15hp and thats about all you can do, without going inside the engine.

What he said.

If you want around 500hp you can do the heads, cam and exhaust. You will need to get the ECU reprogrammed though

If you are interested, I have some used 525EFI (70 Hours) Parts for two engines, consisting of Heads(complete less rockers), cams, sprockets, pistons, lifters and ECM's.

Ray

Whipplecharge it

that is always the question
To Blow it or Not to Blow it?

Isn't the Merc 502Mag the carbureated (Rochester) version of one of their 502's? I ask because I cannot remember.

450-475hp will be very very easy with a 502cid engine. FIRST you will need to upgrade to a better breathing aftermarket exhaust system like Stainless Marine, GIL, Dana or something comparable.

And if 450-475hp is all you are looking for, then you will probably get at least 500+hp by mistake! This can easily be achieved by the GM heads that came stock on your engine. Just have them bowl/pocket ported with some short turn radius work---just very mild stuff. roller rocker arms.

Add a decent upgraded hydraulic roller cam/lifter/springs/roller rocker arms and a Holley 800cfm carb.

Depending on the cam and intake manifold you choose, you will easily be at 500+hp. Have fun

502mags went EFI in about 1994.

I'm in the middle of rebuilding my 502's to around 500 h.p. using the set-up recommended by Mark Boos at Precision Marine. There's no real short-cuts or single component upgrade- you're either "all-in" or you're wasting your money. I'll have close to 10K invested in 2 engines when all is said and done, and that's with used Gil's

If you are planning on keeping the boat and adding further upgrades later. If you are do the exhaust first then do other mods later. It will only yeild you about 1 or 2 mph but exhaust is needed for cam upgrades. I use EMI with long stainless risers.