daddio211

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.

TomZ

iTrader: (2)

Welcome. You didn't mention what boat you're trying to repower, but I'll give it a crack.

The block is good. The roller lifter retainers are good. Valve and front covers. And that's about it.

If you're gung-ho and can get it for next to nothing, you could bore it 030, throw a decent forged rotating assembly in the block (4.25 stroke), decent heads of your choice, something in the neighborhood of a cam to support the heads, good intake and carb (fuel injection will add considerably - the TBI on the 7.4L is of no use), and finally, exhaust that will support the power and not drown the engine in water from reversion. $10-12k, maybe a little less if you can get some deals. Plus there's increased capacity oil cooler, plumbing, fuel pump (most Gen VI blocks do not have a mechanical pump provision). This all adds up quickly.

People here have some pretty decent stuff for sale for a helluva lot less if you start asking. I'd go that route.

TomZ

iTrader: (2)

If you want something within the 500 HP range, Mike Mello (Sick Stinger) has a 40 hour HP 500 for sale over on Facebook for $8500. He'd be able to set you up with whatever you needed.

daddio211

Thanks TomZ, much appreciated info and thanks for the reply.

I tried to include a photo of my boat but can't until I have 10 posts here. My boat doesn't necessarily "fit" here as it's a day cruiser and not really an offshore boat, but it's what I want and I will be making a few Catalina trips in it.

The boat is a 26' 1986 Sleek Ambassador. It has a Merc 260 horse SBC and pre-Alpha drive. I have no idea if the engine runs or if the drive is in usable condition.

The long-term goal is to have a reliable 500 horse boat that can run 70 MPH but cruise all day at Lake Powell, Lake Mead and Havasu. I'd love to go faster but 70 is about the limitation of the hull.

The short-term goal is stuff the 7.4 and Bravo in and get it running for the summer, then pull and build them next winter. Of course I have a rotten bulkhead so I'll be redoing the bulkheads, stringers and transom.

daddio211

I should also mention that I want to build the engine myself, so I'll be looking for parts rather than "take outs" or such. I do know for sure that I'll need exhaust manifolds to exit the transom soon... no way I can stand to have the exhaust exit the drive on a boat like this, LOL.

phragle

iTrader: (3)

that drive will have to go too.... a 500 hp big block wll eat a prealpha for a mid morning snack. but its an easy swap

daddio211

I completely agree. My original post said that the boat I'm looking at taking the 7.4 out of also has a Bravo One attached.

The Bravo conversion is really the largest factor in the whole process, as the pre-Alpha is bound to scatter sooner than later with some power. I'm not terribly concerned with what I chose as the engine as I have a 425 horse SBC and a 525 horse LS in the garage, but for the sake of simplicity I think I'd just transplant the 7.4 and Bravo from the donor boat. No figuring out what does and doesn't convert, searching for parts, etc.

daddio211

This is post #10 for me. Will it allow a pic yet?

daddio211

That was an obvious no. Post 11...

daddio211

The glass and gel are in really nice shape. Interior is gutted (everything was rotten). Again, stringers, bulkheads and transom will be replaced. It will get a color change and full interior in the near future.