Hey guys,

So my 502 Mag is out for a rebuild at the machine shop, nothing crazy just a little kick in power. It is a Gen 6 roller engine with an black MPI mefi 1 system on it, not sure of the exact year engine as it is not original to the my boat which is a 1996 Baja 252.

I am keeping it EFI but thinking about ditching the mercruiser MPI and going to a Holley Sniper or keeping the MPI intake/injectors and running it off Holley HP.

Right now I am trying to select a cam for it, I am looking to be in the 550-600hp range, going .030 for a 509 and 9.5-10.0:1 compression. Debating on dry tip VS the full wet/silent choice exhaust on it now which I know drastically changes cam profile due to reversion.

Looking for advice from people with experience and what they would do if it were there setup. Again it is a lake boat, not looking to race it or be the fastest just want it to be a fun boat that has some pep and sounds good doing it.

To make 550-600hp, you will need new heads as well. Low 500's is doable with the stock rect port heads.
Here are some older threads with great info.

502 MPI upgrade results

Off the shelf cam options for marine engines

Off the shelf cam options for marine engines

how do I make my 454/502 mag boat "faster" ????

Been debating going aluminum but my boat is raw water cooled. It is fresh water only but will aluminum last with lake water flowing through them?

Anodized aluminum heads would work.

What heads are on there now?

Aluminum heads are fine in freshwater, but a decent set of iron heads will be fine too.

GM rect ports would be stock on a 502 mag

Just asked. Stock 088's will make decent power if they have a good 3 angle valve job, good springs and the right cam. Mine is making 650tq and 630+ HP @5300 RPM

Stock Iron rectangle port heads. I was thinking heads would run me around 3k. Am i in the ballpark?

So the summer of 2021 the boat would run 59-61mph and this past 2022 season I saw it struggle to pull RPM and I couldnt get over 58mph but by the end of the season it was stumbling above 4K and could not run over 45-48 so I knew things were going south and before a total failure it was time to pull it apart and thats when I found 2 different head gaskets and the ****ter of the two ****ty gaskets scorched and water was sitting in one cylinder. The head was removed about 5 weeks after the boat was taken out of the lake for the season.

Sniper is not intended for marina use. I know they claim its USCG certified, but it isnt potted or water resistant. Spring for HP.