Upgrading engine and drive?

[Madmooner]

Hi folks - It's the time of year I start tinkering with the boat in anticipation of spring and thinking about upgrades I'd like to make, one of which is the engine and drive.

Currently running an older 260HP Mercruiser 350 with an older pre-Alpha drive. Motor runs good, but is a bit tired. Always lacked grunt, or at least I always wanted a bit more. Drive has quite a bit of gimbal steering pin wear. Enough that I want to address it sooner rather than later. Its had issues with corroded wires and switches over the years but has been serviceable.

Anyway - In my mind what seems reasonable is to build a nice mild stroker in the vein of the HT383 crate motor and possibly re-using the manifolds, carb, distributor, and whatever else makes sense. I'd like to put a brand new Bravo in place of the Alpha but doubt that's in the budget. Seems a lot o wrecked/sunk boats out there with clean and newer Alphas should be available to part out?

Questions are, build or buy crate engine? Where to look for a clean used drive and what to expect to pay? Buy a clean used transom plate and buy a SEI drive?

I'd likely run my motor until I had everything in hand, then sell my set up and install the new one to recoup what I could?



Boat is a 233 formula. I' don't beat on it and would think a Alpha would be fine with a gentle throttle hand?

Any and all feedback and ideas welcome!

Thanks!

 

[harringtondav]

Alpha lls 1998 and beyond, s/n OL100040 and up are built to handle up to 300 hp, if they have the black GKN driveshaft assemblies. These use Bravo unis and coupler. The prop shaft driveshaft is also different, and I suspect beefier.

Not doubting your intentions, but if you upgrade your engine, you will likely use it to it's full potential. So I'd find a drive that's designed to handle it.

Others with more knowledge can recommend a correct gear ratio, etc.

 

[Scott Danforth]

build the motor yourself. you are looking at $3k range for the motor, and about another $1k in exhaust/carb/etc.

Building from scratch is same cost to build a 383 as it is to build a 350 - within a buck of each other

then install closed cooling

without knowing what you have for a year or manifolds, I would say buy new. suggest upgrading to vortec heads, so your existing manifold wont work. suggest upgrading the exhaust manifolds, so your current exhaust mannis wont work either.

regarding the drive

I have personally been on 460hp 383 cubic inch boats with alphas. however they were twins, so there was redundancy. you need to watch the hole shot, and have a rev limiter that kills the ignition if the drive comes unloaded (as in airborne - as the re-entry will shatter the gears if the drive is fully unloaded, then instantly fully loaded)

A bravo would be better as you can beat it like a rental

 

[Madmooner]

Thanks all or the responses.

I have a closed cooling system and would move it over. I was aware that vortec heads necessitated a new intake but do they also necessitate a new exhaust?

I am fairly mechanical but haven't put an engine together in over 20 years. Kinda sounds fun and think I would enjoy it! Just looking at all the variables between blocks, engines, drives, and making a motor that makes sense is making my head swim a bit! Lol.

I'd love to go Bravo. Cost is a consideration though. Seems they are a bit more spendy. I'll have to look into costs and what else extra I would need. I know they have engine mounted water pumps?

As far as a long block for marine use, anything besides brass freeze plugs, marine friendly cam, and proper piston shape (quench and a CR around or under 9.5:1) to consider? Less clearance issues with 5.7 rods instead of 6.00?

Cast steel and hyper fine for crank and pistons?



So many questions!!!!

 

[Scott Danforth]

Cast crank is fine in a boat. Hypereutectic Pistons are fine. Your existing heat exchanger may not be up to the task of more power

 

[QBhoy]

The Alpha will be fine with that engine. Just avoid hammering open the throttle from a stand still and all will be well.
I’m almost sure there were plenty of 7.4’s running alphas in the day. It’s the torque that’s the worry. Not the HP I suppose. For the price of repairing a bravo, you could buy another Alpha new. Be fine !

 

[Scott Danforth]

The 7.4 in front of alphas was a 1988-1990 flash in the pan as the motor tore the drives up. Many were behind big sea rays

 

[harringtondav]

It’s the torque that’s the worry. Not the HP

I'm glad to see someone who understands gearboxes, trannys, diffs. Drive train engineers deal with torque loads. HP is incidental, just a product of torque and speed. Torque loads bend and break gear teeth, cause gear face pitting and twist shafts apart.

Your right hand controls the torque delivered to your out drive. So if your drive is marginal, go easy on the hole shots as mentioned twice above.

 

[Scott Danforth]

HP is how fast you hit the wall
Torque is how far you take the wall with you

Seriously, HP is a fuction of torque and RPM

As far as the alpha is concerened da/dt is what kills it. (Inner geek showing)

 

[Madmooner]

To start this project, I need to get an engine block. Any particular block I should look for?

1 piece or 2 piece RMS?

Anything marine specific?

 

[Scott Danforth]

I would buy a new 1-piece RMS block from GMPP for $750 (cheaper than buying a used block and cleaning/line-hone/decking/boring/honing)

for rotating assembly, get a SCAT (stay away from Eagle). get KB LCQ pistons to match the vortec heads

you will need to mod the heads for screw in rocker studs and appropriate valve springs for the cam you want to run as stock vortec heads have coil bind with lifts more than .420

the marine specific things will be brass or stainless core plugs, stainless MLS head gaskets and compression ratio and cam

 

[Rick Stephens]

Scott Danforth I gotta say that I surely do appreciate the advice you give everyone, particularly on building up SBC motors. Remarkable the amount of stuff you got squirreled away in that grumpy ol' brain. Thanks!

Rick

 

[wahlejim]

Place a call to SEI and pick their brains about the drive. I would go with an SEI unit. Brand new for about $1600 and an unmatched warranty. They stand behind their products. They also sell Bravo lower unit equivalents. I thought I had read somewhere that bravo lowers will mate with gen II Uppers? I could be way off base on this one but it may be the solution to getting a decent drive on a beefed up power plant.

 

[achris]

..... I thought I had read somewhere that bravo lowers will mate with gen II Uppers? I could be way off base on this one but it may be the solution to getting a decent drive on a beefed up power plant.

Nope. Can't happen. Apart from the fact that the cases don't match up, how would you select gear? You'd have the Alpha top, which is a straight 90 degrees transfer, permanently engages, and the Bravo lower, which is also a permanently engaged 90 degree transfer....

Chris..

 

[wahlejim]

Nope. Can't happen. Apart from the fact that the cases don't match up, how would you select gear? You'd have the Alpha top, which is a straight 90 degrees transfer, permanently engages, and the Bravo lower, which is also a permanently engaged 90 degree transfer....

Chris..

I thought it seemed fishy and admit I didn't dig into it too much, but knew someone with your experience would correct me if I was wrong! Either way, if the OP can find a good Bravo upper with a damaged lower, SEI sells bravo lowers for less than $1000.

 

[Madmooner]

Really appreciate the reply’s, all.

I called around and can can get a “running engine” from a local yard for $125. Vortec 350, Said the head gasket leaks but should be in good shape.

As as long as they agree to replace anything that’s not repairable, I think that’s the direction I’ll go. Tear it down, some block work (hopefully minimal), rotating kit, put together a nice short block. I will stick with the vortec heads. Not sure if I’ll rebuild or buy new. I figure as long as I stay with the vortec design and same chamber size I can chose my pistons. That Scat kit with KB pistons looks good.

Not in a hurry. Hopefully will have the motor done by next spring.

 

[Scott Danforth]

Get costs to have your block cleaned, line honed, decked, bored and honed

Then compare to buying a new block