I have stock pair of 454mpi non mag motors and wondering what the best way to get a little more power out of them at least to 400hp or so. they have 400 hrs and run perfect.

With 400 hours definitaly have them checked out before trying to make more power.

A Whipple or Procharger is the best bang for the buck. Otherwise, you will need at a minimun, head work with all the hardware (springs, retainers, studs,rockers etc.), exhaust, cam,etc.
However, I would still recommend some head work with the addition of a SC. You should freshen up the heads anyway since it has 400 hrs. If you do a SC, you should put in a goood set of valves, new springs, and Cometic head gaskets.

Eddie

If it has 400 hours on them leave them alone. If you go adding boost your engines with 400 hours will turn into ticking time bombs. I would decide now what you really wan't in the long run and start getting parts together and just run what you have.

The best option would be to sell your engines and buy some 502mpi takeout engines. The cost would probably be about the same as supercharging them.

sorry to bring this one year old thread to life, but i have the same "problem".

I have a 2000 454 mpi with about 350 hours. i just bought the boat and i am not sure if the former owners have been doing their mainainence and since it is soon 10 years old i was thinking of taking the engine out for this winter just to see if there is some parts that needs to be changed.

while doing this i am offcourse also thinking to cranking the power up a bit. nothing to serious, i dont whant it suprtcharged but i might as well get something done when the engine is out.

does anyone have any suggestions?

oh, and buy the way, i live in Sweden and the only used 502 i can find on the market is 11,200$ so thats out of the question, but lets set the budget for about 5000$

//Emil

your problem is going to be the MPI. You can only get so mush HP out of it. In order to do anything remarkable and keep fuel injection go to aftermarket or look for 500 EFI stuff. Otherwise you could do a little head work, maybe a little bit bigger cam, but that's really all.

Leave it alone and go boating. If its not broke, don't try and fix it.
If you're set on spending some $$, then get your prop lab finished and add a performance exhaust system. Those two things will run you about $3000 USD, or more. You will need the exhaust anyway if you do any real performance upgrades in the future.

Griff, i hear what you are saying.. would your suggestion to tuning an engine be to buy a bigger one? - if i would whant to buy a 502 mpi from US, what webpage schuld i start looking?