captndonzi

Can anyone tell me about my 502? It is a 99 502 mag mpi(425 hp?) that I would like to pep-up. I would like to upgrade the manifolds to GIL or someone similar. Does anyone know if my ports are square or oval? I think this is a Gen 6? I have also been told to go with a larger throttle body, anyone tried this? Do I have roller cam, or roller rockers?
This is in a 99 Donzi 26ZX. if anyone has any suggestions as to upgrades on this engine please let me know. Any help would be GREATLY appreciated, Heath

please don't say supercharge her because I just bought lakefront and I'm building a new house this summer so the "boatbudget" for '05 will be limited, very limited!

BadDog

Stupid answer but save your money until you know where you are at. Then do it right like you want it. You did not buy your property and house with second considerations did you?

Maybe not a bad answer after all.

Welcome to the Board!

As far as your 502 do some research. You will get your answer with a post but you won't learn as much.

captndonzi

Bad Dog,
The reason I ask about the head porting is because I have 2 sets of GIL manifolds that came off my Sonic and I would like to use them if possible, however they are square port.
Also B.D., I don't believe I have owned a boat for over a few months so saving my money till later is usless, just want to have a little fun until someone makes me an offer on this one. Thanks for the welcome, Heath

captndonzi

formulaz,
what would you call the exhaust "hole" then?

wwwTOPDJcom

cheap speed is to have your prop done.. Darin took me from 67 to 70.6
with a 26 B1 labbing is one of the ones that gets ya something for very little cost.

exhaust will gain you unnoticeable speed less than 1mph, unless you have thur hub
in which case it could be slighty over 1mph.

BadDog

Looks like your best bet is the exhaust and the prop. Depending upon how the hull reacts to the prop changes you may pick up some speed with Gills. If the Gills are in good shape selling them would put you half way to a nice low boost Pro Charger setup (dang there is that blower word again)! With that engine a 3.5 PSI Pro Charger is probably going to be the best bang for the buck. Whatever route you go do bear in mind your insurance policy. They are often somewhat void if you have done any modifications without specifically stating such to them.

mcollinstn

All Merc 502's use iron rectangle GM heads ('cept the HP525).

All BBC exhausts are steup to work with the same basic exhaust port. Some header flanges have a little different shaped hole, but they were all designed to "work" on any BBC head. If you're going for the last smidgen of HP, then you would want to match the port to the flange, but that's not the case here.

captndonzi

knowledge is priceless, ...thanks guys

Edward R. Cozzi

I just had a thought.
What would happen if captndonzi bought the 500EFI cam and lifters, upgraded to roller rockers and used his Gil exhaust?