Does anyone know what the 502 mag mpi system will handle in stock form, and can you reprogram the ECM for more power.
I have a 97 502 Mag MPI with CMI e-tops. Looking to rebuild over the winter for max hp. I am pretty sure I will have to get new pistons and perhaps a new crank as well. The engine ingested water and has been sitting for several months before I got a hold of it to drain it. Why don't people drain their engines when they know there is water in them!?!?!?!?
If I need a new crank and pistons, then the sky is the limit........... 540........572........... too much for EFI??

Using my original 2000 502 mpi mefi-3 ecu I made 950 hp (on a 540 w/m-3sc procharger). You could build a 540 and use your ecu and intake/plenum/throttle body. In un-modified form your motor will be about done at 5000-5200 rpm's and make 580-600 hp if everythings perfect and you have good flowing heads. I went a step further last time, bored out the throttle body, full ported the lower manifold. Made 657 hp (NOT turning accesories though) normally aspirated and 1115h turning the Procharger, I was told by Tyler Crockett that at the time he hadn't seen any merc mpi top end make that kind of power. I since bought several mpi throttle bodies and had them bored out to sell on a exchange basis. We saw 19 hp (if I remember correctly) in a back to back test from a stock tbodie vs a bored out one, If you switch EVERYTHING to something more main stream there is probably more hp to be had at about the same cost plus you can sell all your mpi parts but thats up to you, Smitty

The ecm doesn't really have a limit. The biggest problem with yours is that it is a Mefi 1, if it is a 1997. That ecm has no way to tune it boost, so you will have to stick with an N/A engine. Procharger has a setup that will compensate with increased fuel pressure by using a rising rate regulator (3:1, 5:1, etc) That is a band aid and honestly doesn't work that well. However, you can cerainly build an NA engine that will make quite a bit more power than you currently have.
The single biggest improvement would be to lose that intake if you want to make much over 550 hp without much trouble. That intake will make 600 or more, but takes quite a bit of work to get there. You can replace it and instantly pick up quite a bit of power.
How much power are you looking to make, what's the budget, what type of boat, what's it's current speed and what speed would you like to run, etc.? That would be the best place to start. Give me a shout if I can help.
Eddie

Thanks for the input guys, It is a 1997 fountain 27. I don't need to go crazy as there are not that many lakes here where I boat to justify anything over say 75mph. I believe the boat was about 70 mph with 425hp at sea level in stock form. Most of my boating will be from 3500' to 5200'. I still need good holeshot to pull the kids around when they want to and like I said would love to see about 75-78 here at altitude. I would like to stick with the MPI just for the sake of buying more parts than I absolutely have to at the moment. I will probably be putting crank, rods, and pistons in at least and a new cam due to water damage.
So with all that in mind.............. am I correct in thinking I probably need about 500-550 hp? I have the cmi e-tops so I won't be limited by exhaust, just what the computer will run well with.

Oh, and budget? well like most on here I work for a living and not made of money. I think I can probably spend about 2000 more than if I were to rebuild it stock. I will assemble the engine myself and have the machine work done.
So If I can stay under 2,800 or so in parts that would be good.

You will need more power than that to get to 75mph at 5000ft. I would say you need closer to 600HP to hit 75 and that is dynoed in Denver. I would go with the 540 rotating assembly if you have to replace the crank, rods, and pistons. Your budget doesn't give you much leeway for improvements. Everyone needs to remember that you will loss %15 HP at this elevation, so to get 600hp the motor needs to put out 690hp at sea level. Most boaters in our area that want to go faster put on blowers to make up for the loss in air density due to the elevation.

You will have to double your budget to build a 540.

$2000 stroker kit
$2000 cam and valvetrain (lifters, push rods, valves, springs, rockers)
$1000 machine work (clean, bore and deck block, balance rotating assy, resurface and rebuild heads)
$350 ECU reprogram
$300 bigger oil cooler
and you still need to buy gaskets, belts, hoses, oil and filters and an adjustable fuel pressure regulator.
Then you will have to get the new engined tuned either on the water or on the dyno.

Like I said, might have to triple the budget.

I second that Snapmorgan! And the extra cost to upgrade the fuel lines, fuel pump and new prop. If you can't come up with the extra $$$, just give it a quick overhaul, if it is salvagable and run it until you can upgrade later. I do my own rebuilds also, and it always cost $5,000 or more everytime for a BBC.

Thanks guys, I think I'll probably rebuild it to stock specs, maybe a little more agressive cam, and think about an s/c down the road.
What is the best side mount s/c to look for used?

What if you just swapped the intake for the HP500 intake from AZ? Would you need to change anything else? Reflash or would it work as is on an MEFI1?

It would be an easy change for some power if it would work alone.