cableguy1979

I'll be happy with a stock tune but if I have to spend $500 for a performance tune I think I might just try the 454 mag tune. Literally the only difference is cubic inches I cant see the computer knowing that much of a difference.

Trash

I will touch on a couple of points and reiterate some others.

I would not raise the rev limiter. You would likely be exceeding max hp curve and not see any improvement in performance. Heads and cam might benefit from an increased rev limiter but not in stock form. I also would not alter the idle unless it is way off.

The MEFI controller only holds one .bin file at a time. You cannot 'switch' between tunes on the fly. You would have to load the tune each time you want to make a change. A MEFI 1 loads in about 3-5 seconds. MEFI 3 takes a little over 2 minutes (PITA).

Run the motor with the existing 454 tune THEN see where you need to go.

articfriends

iTrader: (1)

Gen V 454/502 had 48 lb honda/keihan injectors, gen VI had maghetti marelli 45/46 or so lb so possible a mefi1 with original tune will be 3 or 4% leaner but I wouldn't get crazy worrying about it as mercruisers are pig rich from factory anyways. I sent you a PM on tuning your ECM, Smitty

cableguy1979

So this makes me wonder if the tunes from the 454 mag mpi to the 502 mag mpi are any different. They both, in Gen V used the same injectors. However, Im running a Gen VI 502 longblock so the cam would be different since its a roller and from a MEFI 3 boat. I have a bad feeling I may have messed up putting a 502 GenVI long block in place of the 454 Gen V. Noone seems to know if the tunes were any different from 454 to 502 and GenV to GenVI so I have no clue which tune to offer the motor. I do know the GenVi motor used the same internal parts minus the pistons and cam.

Trash

To the best of my knowledge the Mag/EFI motors were all hyd roller cams. I would need to dig out my literature, but I know the small block motors were. Don't over think the GenV and Gen VI stuff. Run the 454 tune on the 502 FIRST. Then see what needs to be done. Like Arctic said the factory tunes are pretty rich/safe assuming your fuel pressure and injector sizing is factory spec.

I have personally run a bone stock factory MEFI 1 tune from a 350 Mag EFI/MP motor in a 377 stroker, WAY bigger cam and heads and it lit off on the first try and idled on its own. AFRs were in the mid to high 12's at idle on the modified motor and stock tune. Hardly dangerous as a starting point. I am confident you could do the same. Either tune the 454 .bin yourself (requiring wide band which is easy) or hit up Bob and MEFI Burn or for a 502 tune.

SB

iTrader: (1)

Nope. Even the Gen V 502 MAG MPI was flat tappet.

Trash

Thanks for the clarification. You forced me to dig out the old brochure. The verbiage in the paragraphs in the 1995 Mercury brochure would lead one to believe they were roller camshafts, but the actual motor listing shows only the small blocks and a few 'blue' motors as having a roller cam.

Regardless, for the OP, the difference between the roller cam and a flat tappet as far as EFI is concerned is nil in my opinion when comparing the factory cams.