HOTTZU98

Can a 7.4mpi be rebuilt to a 454mag? O r would it be more cost effective to sel a good running 7.4mpi and buy a rebuilt 454mag? Would the fuel system from a 7.4 be compatible with a 454mag? Thanks fo any info. Ball park what is a usede 7.4mpi worth it had a great leakdown test and runs great 400hrs now.

Whiteknuckle

If you are only looking to get the output of a 454 Mag out of your 7.4 MPI, and it is running good, leave it alone. I don't know what kind of boat it's in, but 30-35 HP is not worth the hassle. Just my .02.

BajaRunner

its 75hp difference. I too have thought about it. my boat with mags is 10mph faster.

BajaRunner

but then i think about how good they run and i dont want to d!ck with them

Whiteknuckle

Somehow I was thinking 365 HP vs 330 HP. My mistake.

Mudball

I would look for another engine, and keep yours for a spare or sell it...

I had a 7.4mpi with 165 hours in my 22ZX Donzi. I found and bought a used HP500 with 180 hours on it for $7500. I then reworked it and added some things and ended up with about 10k in it.
I then sold my 7.4mpi for 3k.
So, I have about 7k in an HP500!!!

You should be able to find a complete mag of some description for not a huge amount of money.

Take care,
Kent

Pat McPherson

I tried to hop up my 7.4 MPI last year with a bigger cam and good exhaust. The re-calibration of the fuel injection became a big hassle to say the least.
I have also been told that the GM MPI intake will not flow enough to make power above 4600rpm so this limits the potential output to about 375HP.
The base L-29 engine is an OK base to build up if you are willing to ditch the fuel injection for a carb. It is a roller cam engine with 9:1 compression and vortec heads.
With the right cam, intake, and carb, 420 HP at 5000rpm is not all that far fetched...

SeaRay Jim

Been there done that too!! And Pat hit it on the head. I stuck with the MPI and should have gone carb.

Another member bought my heads and cam and had bobl do his for him. Only difference was his is/was a Volvo and he did go carb. He's somewhere in the 425-450 HP and for the money (saved a lot buying my heads and cam) got decent performance. To do it all, it's probably not worth the money. You could probably buy a good 454 MAG for the money.

I ended up with a new 540.

Mudball

SRJim, hows your stationwagon runnin these days? Blown away any Fountains, lately???
Yup, I saw your bad boy at FTM!!!!

Did you get your props ironed out?
Kent