502 Mag MPI Tunability?
 

Have a lead on an early 2000s 502 Mag MPI with a likely cracked block. Comes complete.

Thinking of swapping it over to my 454, or just finding a 502 block to swan into.

How tunable is the 502 EFI?

I would likely port the 454 heads or source good aftermarket. So flow and hp wouldn't be too different.

mefi1,,it can be tuned

I converted two carbureted 502s to used Merc MPI systems several years ago. After a couple of frustrating years dealing with the MPI, I switched to Holley HP TBI.

Since then, I’ve logged over 1,000 + hours with the Holley—mostly trouble-free. The best part? The "Self Learn" feature. Tuning the MPI was a real pain, but the Holley system made things much easier.

FWIW

Steve H

So you are considering placing the 502 MEFI stuff on a 454 correct? Yes it will work and yes it will be tunable. It will require, in my opinion, very little modification in the fuel tables and perhaps the timing table. I would disregard the nay sayers. I've been using and tuning a MEFI 1 for 30 years.

so you have a early carbed 454 or5 something? a 2000 502 would have mefi3, anyone skilled in tuning efi/mefi who has a base program can tune it, have injectors flowed, cleaned and tested as insurance, I sometimes see issues with them when I flow and clean them at my shop fwiw, Smitty

I bought a stripped '99 Baja Boss 232 for the trailer...turns out the boat is pretty nice. It doesn't owe me anything, and I have spare parts around. There's still a Bravo transom on it, just needs a drive. Has he secondary external steering rams, I was going to us on the Forumula 233. Even toy'd with going Bravo on the 233.

502 marine engines are pretty rare around the PNW. Unfortunately, despite a written and verbal deal, sold it on me. A few other friends have commented there's been issues with people just selling advertised items, despite planned arragnements to buy etc.

Maybe it's a region issue?

Anyway, back to the carb plan...lol.

what equipment is required to interface with the Merc computers etc? I like the reliability of carbs on a single engine, and digital Ignition like the Daytona coupled with Wide Band A/F carb tuning gives the best of both worlds.

SITREP:

Managed to find a 7.4 MPI complete.

It's in core level shape, but that works better for my plans etc.

The Baja 232 hulls won't benefit from anything over 400hp area. They don't like more than 70mph. So there's no point in pushing past 400.

What HP (flow) will the MPI intake support? These are RPM limited like most GM long runner EFI intakes. But if they support a 502 at 5000, I would expect a 454 would be choked off for flow around 5400 area.

Likely far easier to run a good carb and intake, and there is room for that in the Baja.

My Formula 233, has very little room for height in the engine cover system that incorporates the seating. So an MPI intake would benefit here. But I was looking for more HP for the Formula hull, around 450 ish at 5500rpm.

Will the intake deliver that with the better throttle body gasket?

How reliable is the MPI system?

I believe you can attain the HP goal you are looking for with that system, assuming the injectors are sized accordingly. I can't speak for all MEFI systems but my 1995 era MEFI 1 has been very reliable. I have had hundreds of tunes thrown at it. Injectors getting balled up from sitting with crappy ethanol fuel would be the biggest issue, but as long as the engine is run on a regular basis that is a non-issue or if there is sufficient fuel treatment used.

I not a newbie for FI, but have not touched marine EFI systems.

Flashing software is pretty steep these days. Is there a few different options? Hardware connections?

Why not do a Holley ecu and harness for the mpi, the self learn is great and easy to tune if you go bigger cam etc. I still use the commander 950 system, reliable and tuneable.