5 MPH increase with better spark plugs? You'll have a hard time convincing me of that.

catmando can you give more info on this vortec kit?

Cat,

What do you mean the 502 internals are not as strong as the 500EFI. The block, crank, pistons, and rods are the same. What is different the cam, heads, intake, and exhaust? Im not sure what heads or valvetrain the 500EFI has but the 502 Mag is a good candidate for supercharging.

Ron

If you ditch the EFI it is worth at least $1000 on eBay......That should help offset some of the costs...

Ken

That 502 comes stock w/ 390hp(you probbably already know) just built mine carbeurated motor, angle cut and polished heads (original) replaced valves with the Manley one piece went 30 over on the block with JE 700 forged pistons and Competion ground a special marine app cam. and went 440hp @ 4900 I know that dont sound like much for all I spent but spring melt down left little choice. I om very pleased with the boats performance. We run about the same length but I probably easy 7 to 900lbs heavier. 50 horse upgrade is a hell of a lot of difference. I really wanted reliability over unpurchasable hp for my budget just a .02 ct piece
jrocket

Buy my Weiand 177 blower/manifold and run some boost through that bee-aatch.

joey O

The bottom end of a 502 mag is very tough. I wouldn't want to turn it over 6500, but then again how often do you see that in a marine engine? I turned mine 6000 with no problems. I know several drag racers who regurally put a 250hp NOS shot to a stock 502 bottom end and have never had any issues.

Forgot to mention, I ran GIL exhaust...because it was already there.:rolleyes: :p Never any reversion problems with that cam and it was a thumper, idled great though. :cool:

Cat

I belive the 500 is the only engine from the Merc Racing line that is not hand built. They buy the shortblock from GM then assemble using parts from GM and other vendors. They may even buy the engine with the heads already on it.

Ron

Thanks for all the responses....wow, I have my hands full now. I'll keep you posted on what I end up doing. Keep the recommendations coming though, they are much appreciated. Tantrum, let me know for sure when you get up here again next year. There are some great out of the way spots to show you. Time to start staring at the Calender now.......what is your boat now?

Tyler Crockett offers a (500hp) 502 EFI Upgrade He does quite a few of them with great results. See: http://www.azspeed-marine.com/articles-1a.html Some of the dyno numbers in the article are mis printed but the end result is about 500 Hp + extra reliability. I think the $$$ suggested include Stainless Marine manifolds and risers.