Dutchboy

I took out my 2000 502 mag mpi out of my boat to freshen it up. (somehow water got in manifolds after winterizing and a couple valves stuck open) it is stock, with stock injection. I had the heads opened up a little bit and going with a 2.25 Intake and keeping the 1.88 Exhaust valve. SS valves, brass guides. Also adding a set of Stellings dry headers and tails. Basically what Im curious about is, Do I go carb and cam it? or keep it stock injections and leave the cam and mods alone other than the heads and headers. I really dont want to mess with the tuning aspect of EFI. What carb would be efficient? Holley 750 DBL Pumper? What Cam? Crane 731? I have done a bit or searching and these are some of the parts ive noticed to similar set ups. My boat is a 1996 velocity 260 with eddie marine tabs and im currently running a 28p 4 blade prop. not sure how much of that matters. any info would be nice as this is happening over the next couple weeks

AllDodge

iTrader: (1)

I think unless your willing to measure AFR's then stick with what you have, otherwise; building the motor and not knowing can put everything in the toilet

Trash

With some simple head work and valves you do not need a tune. I would highly recommend adding a wide-band set up even in stock form so you can monitor what's going on and get some baseline data.

Should you decided to modify the motor later, and as long as your HP goal is within the limits of that Merc intake, I'd leave it EFI and tune it. It is not any more difficult than rigging, installing and tuning a carb. In fact I'd argue its easier.

Dutchboy

Your not suggesting I cam it any? I'm good with getting a wide band, is there a special one for marine applications?

dereknkathy

What you will need for the wideband is a place to mount the O2 sensors. Varies with each type of exhaust. A couple of guys even rigged up ways to run O2 sensors in thru the exhaust outlets for a temp rig to get afr's set right. That is the 415 hp 502 magnum? You would need intake and especially exhaust upgrade to run any more cam.

Trash

You can modify the motor to your hearts content. I'm merely suggesting the existing intake manifold on the 502 will only support a certain amount of HP before it runs out of steam. Don't throw more cam, head and cubic inches at that intake than it can handle.

You would likely be able to make a strong 550-600 hp motor with appropriate injectors, heads and cam and exhaust. This of course would require wide band and ECM tuning.

Jonesyfxr

iTrader: (1)

Call Tyler Crockett. He did a 502 engine in a friend's Sunsation. The boat is a beast.

RaceRPM

Another option, call Bill at Ateco Marine. He has many options for the 502 MPI. He did mine and I am very happy with the results.