Anyone ever build up merc 454efi 310Hp? Mine run perfect with 400 hours on them but want more power and thinking of freshening up and want another 100hp. any ideas? Thanks

It would be cheaper to sell yours and buy some 502mpi's. Your engines are not really good candidates for upgrades.

Griff is right. That motor doesn't have any good components in it. Cost more to upgrade than to sell it and buy a 502.