Wow, I am suprised by the MSD. I always thougt that the merc ignition was pretty damn good. Interesting though.

You need to compare the Propshaft horsepower..ie, 502mag = 415psh & the HP500 = 470psh add 30hp to get the crankshaft horsepower for each engine..FYI, the 525sc is a blown 454 that made 490 psh... the HP600sc is blown 502 and made 550 psh..the 800sc is a blown 572 and made 700psh..the 1000 sc was a blown 542 with high compression 9:1 ! and made 950psh !!! yikes..all the other blown mercury engines had 7.5:1 compression....also, the 525sc had a single 1050 carb..the 600 & 800 both had dual 700 holleys & the 1000sc had twin 1050's! they all had 4800-5200 RPM range accept the 1000sc it just had "run me @ 6200rpm" stamped on it!

Well there are a couple of things...(A) your motor is not a true '2002' HP500 because Merc stopped building carbed HP500's in 99'. (B) If it has a 02' serial number, then someone has already scrapped the fuel injection. It would be helpful to know which motor you have because they had a cam for the carbed and a cam for the EFI which are quite different. Non the less, since you are already cabed you have a lot more options..some of which have already been mentioned....:drink: But the huge hang-up with the regular EFI stuff is the very restrictive intake manifold and from what I have been told its very hard to make them flow enough to support better heads, etc...can the intake be modded...sure...but its only money....:p :drink:

The motors were bought in 2002 but were carbed so they must have been left overs from 99 i guess. It looks like the heads and the cam are the way i will go, what heads should i go with or is it cheaper to just port the stockers. Also what cam will i need to go with. Thanks for all the info guys.

probably similar price if you just buy soem good aluminum heads and blot them on rather than remove disassemble, port, ressemble and install the stockers.

Just my 2 cents.

I think the 500hp's are around 517 horse? 470 ish at the prop?

If 550HP is your goal the stock heads should be fine with some bowl porting and a valve job.
For 600HP, it may be more cost effective to buy new heads.
RMBuilder is man to select a cam to maximize the power of your combo.