310 and 330?
 

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. :D To my knowledge the engine is exactly the same.

330 or 310
 

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+.

Is the 454 your refering to a magmun or is it the 454 that is the 7.4l, both 454's but different engines

Referring to the GM L-29 7.4 MPI 340crank /310 prop HP engine - not the 454 magnum.

The carb 7.4L is 330 HP at the crank, and 300 at the prop. The injected 7.4L is 340 HP at the crank, and 310 at the prop. In actuality I think they are the same motor, but the injection is worth about 10 HP. Right? How much is the price difference between these motors?

the heads are differnt on the 7.4 mpi they are the oval but use the vortech tech to burn the fuel better.

Ive heard the intake was bad also, I think there is a shop that ports and mills them

I have heard same thing on the Intake plenum as well .Just remember that the 310 mpi has the little rods ,cast crank,and cast pistons.The block is a gen 6 4 bolt mains same as newer 454 mag mpi.Cam is milder.
Dave

I would like to get 50-75 more hp and Ill be happy with the motor any more than that Id move up to a differnt motor

Not trying to advertise, but i've got a Mark VI Magnum roller cam that would slip right in with no spring changes or anything. I was always gonna do this to my motor, and never did. It's brand new. You can contact me offline if your interested. On a desktop dyno program, it indicated it would make about 30hp at 4500rpm than the stock mpi cam. The specs for both are:

Stock cam that you have:

.480 lift intake
.483 lift exhaust

206 duration intake
211 duration exhaust

119 centerline

The mercruiser magnum cam specs are:

.483 lift intake
.483 lift exhaust

224 duration intake
224 duration exhaust

115.5 centerline

The springs in the vortec heads are good to .500 lift, and the roller lifters just swap right over to the next cam, so other than tearing your engine apart, it'd be a no-brainer. I'm not sure how the computer would react to the new cam. That's the uncertain part....????:confused:

how much for the cam?

Got any marine cams with 112 or 113 LSA?
115-119 god, can you even hear them?
LMAO
Jason