why did the 454 hp drop from 330 to 310 did they rate it differnt?

It's the same engine with a new umpire that has a new whistle. To my knowledge the engine is exactly the same.

CRMAX I believe the difference is only in where the HP is rated at. Earlier Mercs were rated at the crankshaft. They now rate at the prop shaft.

I have a 97 7.4LX MPI rated at 330 at the prop, 350 at the crank. That engine was discontinued in 97. It has the Merc injection, not the GM like the 310 has.

I know the heads were diffent since 97 I think, the differnt fuel injection may be the differnce but its hard to believe 20 hp diffence

When I was doing a swap from a old school motor to a new school motor I was told they were exactly the same just a different way of measureing the power. The 330hp motor is the same power as the 300hp gen 6 motor.

Jon

It comes down to where HP is measured. The 310 is a little stronger than the 330.
310 Measured HP at propshaft
330 Measured HP at flywheel

Ditto. The 7.4 MPI is 310 HP at prop and 340 HP at crank. The 7.4 MPI has a roller cam and better technology, Vortec heads to get the extra 10 HP.

does the 7.4mpi have a mild cam in it? there has to be something that is holding it back. 310 isnt bad hp but i would think it shouldbe pretty easy to get it up to 360 hp

My understanding is that the 7.4 MPI GM intake system leaves HP on the table and the cam is mild. Many people have modified base 7.4's (with carb. set-ups) to 400HP+.