Offshoreonly.com - Rebuilding two 1987 Merc 350’s

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

- General Boating Discussion (https://www.offshoreonly.com/forums/general-boating-discussion-51/)

- - Rebuilding two 1987 Merc 350’s (https://www.offshoreonly.com/forums/general-boating-discussion/354748-rebuilding-two-1987-merc-350%92s.html)

Rebuilding two 1987 Merc 350’s

Good evening ladies and gents,

I am pulling my 1987 Trojan 8.6 meter express out of the water soon and am looking to rebuild both engines. I have two Mercruiser 5.7’s with 4bbl Qjets and alpha1 outdrives. I am going to have the machine work done locally and build them myself. I cruise on plane around 27 knots. I wouldn’t mind adding a bit more hp but would LOVE to crank out some more torque. Should I stick with a stock 350 setup or push it up to 383’s. I have read quite a few threads similar to this but most people are working with newer engines with TBI or MPI. I’ll add that I AM a mechanic so I am definately gonna be doing this on a budget. Thank you all in advance for sharing your wisdom.

Billy

383 by far. With the cheap price of aftermarket rotating assembly's now it's crazy to build a stock stroke 350. To take advantage of the cubes you will then need to upgrade cam/heads, intake, carb. No reason to add cubes and then restrict it with stock parts.

Lastly, torque and alpha 1 don't like each other. Especially on a heavy cruiser. What's the condition of drives? Original?

Quote:

Originally Posted by Ryan00TJ (Post 4632854)

Original drives. I have been looking at 350 long blocks. It looks like the cheapest way to go since I am also concerned about overpowering those out drives. I’ve read where some people say it’ll be fine while others say it’s a ticking time bomb.

I'd go 383. That's what I did. I run a single Alpha on a 4000 lb hull with a good amount of deadrise. So there's quite a torque load on the drive. I don't boot it, just ease it onto plane. I don't go wide open til I am well up on plane.
If you prop it so the engine will spin up to 5000 rpms the drive won't be as loaded with torque as it would be if the engines can only get 4500 r's. Plus it will make more HP at more rpm.
Well thought out 383's will put down probably 100 ft/bs more torque than the 350's. I have Amsoil Severe Gear in my drive. I ran it a little hard last week with a full load of fuel and people after solving some engine running problems this spring. I think the gear oil got hot. There was some drive oil expansion onto the exterior of my drive reservoir. So I put on the drive shower that I had bought last year and hadn't taken the time to install yet.

Whatever you build make sure to use marine ring gaps. They are bigger that car gaps, similar to towing gaps and usually a touch smaller that turbo/supercharged ones.
You can also do a pair of 355's with good quench and compression. They would definitely outshine 350's and you could keep your crankshafts.