What is the difference between a 454 MPI and a 454 EFI motor?

Are you referring to the 454 Mag MPI(385 hp) vs the 7.4 Mpi(310hp)?
If so, the mag motor is a 4 bolt block with all forged bottom end and rectangle port heads.
The 7.4 MPI has a 2 bolt block, cast crank, 3/8 rods, cast pistons, peanut oval port heads with smaller valves,etc. Not a good platform to modify. The Mag motor is a great platform to build some power.
Eddie

THere are two types of fuel injected 454's. One has two plastic covers on top of the motors. The other has a flat and level plenum with description label on top. Is this the difference you have stated Eddie?

Yes. The one with the flat plenum(it is the same manifold as the 502 Mag) is the 454 Mag mpi. The one with the plastic cover is the 7.4 mpi.
Eddie

Not trying to controdict anyone but I believe the NON Mag EFI engine has large oval L-29 heads. My engine was originally a 330HP carb GenV and it had 4 bolt mains. Not sure about GenVI blocks. The specs seem to change from the year and version of block.

I had a 1998 Gen VI 7.4 MPI. It was a 4 bolt block with L-29 oval port heads. All internals were cast. As stated not the best platform to build up. I acquired a 502 Mag MPI for my build up.

MPI indicates multi-port injection as opposed to a throttle body injection system. But both are EFI or Electronic Fuel Injected. One is more performace oriented than the other.

This is good. Thanks.

The 1994 and 1995 GenV 330hp carbed are 4 bolt - I have 'em, bored an stroked to 496. Solid 600 hp with Crane 741 and Dominators.

Just my .02.

Yes but the 7.4 330hp MPI is actually the one they call the EFI and that is the difference!
Puzzle solved!
Thanks everyone.

WAit... is the 330hp 7.4 really a MPI or is it a throttle-body?