I have twin 454 mag mpi 385hp now with almost 700hrs in a 2000 29 outlaw. Looking at options for rebuilds. This may be out there but if I got new 502 long blocks, how much of my 454s would swap over? Could I reflash the computers? Are the intakes any different? Any other ideas would help. Not wanting to go to crazy as I WILL be moving up to a Cig !. But I also know it will be tough to sell with the hours on it now. I am original owner and have been religious with oil changes and maint. Thanks in advance for any advice.
Quinlan

if they are running good i would leave them alone untill you get the cig. those motors if well taken care of, can go along way

everything will swap over, just keep gen IV to gen IV and so on, as far as relashing the computer, can't help you on that one, but somebody on here will ba able to tell you..Rob

700 hrs on 454 mags if maintained well should still be running fine....the hours will hurt re-sale, but you won't sell it and re-cover the amount the long blocks cost you. Do compression checks and oil anaylsis on the motors to get a better idea of what is really going on with them.

Does anyone know if there is any power to be gained or lost by changing the 454mag mpi 385HP long blocks to the 502-415 long blocks purchased from venders other than Merc? My friend had his 454 long block changed to the 502 along with a reflash on the ECU and lost power. Are the camshafts in these 502's any different than the Merc 502 long blocks? Do you need to change to larger injectors? He was told there would be an increase in power, but instead received a backwards improvement with a loss of rpms and speed. Thanks

That would depend on what company's/vendor's 502's your talking about. The cams in the Merc 454/385 and 502/415 are the same. You would have to compare the the specs.

Thanks Griff
I will compare the cam specs.

Thanks for the update. I am in the CIG now!!!!!

worthless without pictures!

That is true, however, I went from Gen V longblocks to gen VI and found the only difference was the 7/16 accessory holes in the block so some of my accessory brackets needed to be drilled out with larger clearence holes. no issue with oil pan, valve covers, manifolds, etc. Lightning Performance is doing the same thing for me, swapping out my 454 longblocks with 502's