Offshoreonly.com - Merc 7.4 LX (TBI) potential?

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- Classic Offshore (https://www.offshoreonly.com/forums/classic-offshore-199/)

- - Merc 7.4 LX (TBI) potential? (https://www.offshoreonly.com/forums/classic-offshore/375622-merc-7-4-lx-tbi-potential.html)

Quote:

Originally Posted by TomZ (Post 4831086)

The block is good. The roller lifter retainers are good. .

Are you sure about roller lifters? I didn't see a year mentioned and my 1996 MPI has the high wear rate solid lifter system.

Depends on the year. Can be a Gen V or VI. Gen 5 would be flat tappets; Gen VI, roller with the resulting hardware. My assumption was a Gen VI. The block itself was more a focus than anything because it would be a 4-bolt.

Your 96 I’m guessing is a Gen V, right? Stamped steel timing cover?

Quote:

Originally Posted by daddio211 (Post 4831057)

Howdy folks, new guy here.

I'm looking at an older boat that was repowered recently (last 10 years) with a 7.4 LX and a Bravo One. The boat is nothing special, but the engine and drive are what I'm looking for to repower my current boat.

I know this Merc is rated at a measly 300 horsepower and I'd like to do a mild performance build, say 500 NA horsepower. It was suggested (by a member of Classic Offshore Boat Restoration on Facebook) that I ask here.

What are the drawbacks to the Gen VI block, regarding performance? I've read they're a slightly thin casting, boring 0.125" isn't possible, but I don't think I'd need an 1/8" bore to make decent power. How are the heads on these? Ample for 500 horsepower, or should I be looking for better heads? I've read some conflicting info, but it seems that these engines have a cast crank. Is throttle body injection sufficient?

Help me out, if you would please. I've built a few hot rods in my time and have had a handful of boats, but never really gone this far in the boating world.

Its a good engine in stock form but really not a good candidate to try and build to 500hp. Its probably a 2 bolt block and has cast internals and has peanut port heads

I appreciate all of the input fellas.

There’s potential in a 454 tbi engine ?

Someone please correct me if I'm mistaken, but I believe the 7.4LX used the same intake, throttle body and components and the 454MAG and 502MAG EFI's. With that being said, it certainly has way more potential than a typical 7.4 MPI?

Quote:

Originally Posted by Cory H (Post 4831585)

Yes, same intake as the Mag MPIs, but I think the bottom end was not like the Mags, it was like the 7.4 MPI, relatively weak if power added.

I have that motor, 7.4 lx mpi. Its a gen 6 roller, peanut heads cast crank and little rods vst....etc....

So I think I'm going to buy the engine and drive. Before it goes into the Sleekcraft I'll pull the pan and heads and take inventory of what's there. If it's a 2-bolt main I'll plan to have my machine shop drill for a 4 bolt main, splayed if possible. I truly appreciate all of your help.

Quote:

Originally Posted by phragle (Post 4831588)

I have that motor, 7.4 lx mpi. Its a gen 6 roller, peanut heads cast crank and little rods vst....etc....

Good to know about the rollers and heads, thanks! I'll start watching for a set of good heads to make it flow when I rebuild.