Looking for some recommendations on my engine rebuild project, The engines are 502 mag mpi, Due to some wear they are at the machine shop being bored to 509s right now. I have been here searching and reading about cams and 502 builds for weeks, but it seems most are looking for more power than I am. The boat is a Formula 400ss that will mostly just be used for cruising, but, while i have the engines apart... So I am just looking for suggestions,
-What cam could I use? Currently have stock exhaust manifolds with silent choice.
-One of the engines has been apart before and has the better, H-beam rods (weird,that seems to be the only upgrade) should I get a set for the other motor?
-Use the JE forged replacement pistons, or is there a better choice? I don't want to be stuck using premium fuel, I plan on burning a lot of it, compression ratio suggestions?
-I'm told that these heads flow pretty good for this level and to leave them alone, true or? What about better valves, anything to gain there? I would use the springs that go with the cam.
Any other suggestions? I am trying to keep cost down as much as possible for now, might do more later (exhaust, intake work ecm...) I can do that in the boat.
Thanks!

Honestly I'd just be more concerned with rebuilding them correctly and not look for much extra power unless your going to change the exhaust. That cast or Gil's. Have the heads properly gone through and replace the exh valves with inconels and severe duty stainless intakes. Have springs checked or replaced. Depending on what exhaust you have you could maybe up the cams a bit but with limited budget and do mostly cruising you'd have to make some major changes to see any noticeable gains on that 40'. The H beams aren't necessarily better by any means. Stock 7/16 i beam are plenty strong and a great rod.

Post what exh you have. I have a feeling their the cast manifolds. That will dictatate what your limitations are on cams. Btw what castings are those GM heads. Just do a good job on rebuild and I'd keep comp 9.0:1 or less.

^^^^^i agree,the 502 mpi came with merc cast iron exhaust manifolds and they really limit cam choice.i think for your boat rebuilding to stock is the best route to take.i would for sure mark the injector location,then remove them and send them out for flow testing&cleaning.as part of the rebuild.

u might lo0ok at a simple upgrade to the( crane 731 I think) cam that was used in the 500 efi engines. and yes the h beam rods and je pistons stainless manifolds or emi manifolds are good choices for the money and ofcourse an ecm reflash

the 500efi engine did not use a crane 731 cam and they did not come with merc center rise cast iron manifolds.a 731 with stock manifolds will no doubt have a reversion problem.

I know there is a roller cam upgrade out there that does not require a reflash, although I dont know the number. I believe those black motors came with flat tappet which todays oils do not work overly well with.

the 502 mpi engine comes with a hyd roller cam but it is very mild.

As a note: Gen VI had the roller cam. Not the others.

good catch sb,i am so used to gen6 stuff that i forgot about the gen5 having a flat tappet cam but the last gen5 was made in 1995.

Personally I'd get away from the JE piston and the metric ring pac, maybe take a look at Wiesco pistons, the dimple rods in the other rotating assembly are fine, no need to get H beam, unless you want it all to match