3.0L to V8 swap...

I was wondering if anyone was able to shed some light on an idea I have. I own a 1991 Glasstream 19' Cuddy with a 3.0L and Mercruiser Alpha One drive. I bought it at auction for $2000, and I think I got a pretty good deal on it. But after running it for about a month now I can see that it lacks power. It's not a problem with the engine, it really runs great. It's just that I need more power than a 4 cyllinder engine will give me. I would like to swap it for a V8, and I see that I can buy a crate engine for a few thousand dollars, complete and ready to run. But, I can see from looking at the V8 and looking at my inline 4 that the exhaust and cooling is different. What other modifications would I need to make in order to make this swap work. Is it possible to buy a kit to adapt the V8 to the existing exhaust and water port (or whatever it's called) or will it be more difficult than that?? I appreciate any help I can get here pointing me in the right direction, as I want to buy everything I need and make the swap over the winter.

 

Oops....

I'm pretty sure I posted this in the wrong area now. My apologies, can the moderator or someone please move me to the correct area which I assume is propulsion. Again, stupid me, I know better than to post before reading more. Sorry guys!!

 

Hi JnD,

My first question would be, what's the weight difference. (Which V8 are you thinking of?) With a sterndrive boat, when you upgrade the engine, all of that extra weight is right at the transom. If the boat wasn't designed to handle that kind of weight that far back, it will lift its bow too high when coming to plane, making it hard to control. A 19' cuddy will probably have enough buoyancy back there for an engine upgrade, but it's worth checking to see if any of them shipped from the factory with a big engine.

If you're confident the boat can handle it, here's a few things to consider. The engine mounts will probably be in different places; there may not be enough clearance to the engine hatch with the new motor (ie. a new engine bay cover might be needed); the gear ratio in the current drive will not be suitable for the new motor (ie. replace either the drive or its internal gearing); the propeller will need to be changed, etc. You'll have to ensure the exhaust and cooling are adapted, of course, as well as the fuel system and electrical harnesses. There is a chance the old instruments might be incompatible with the new motor. And the installation has to be done to meet the appropriate safety codes.

 

Answer....

The particular model of my boat shipped with inline 4, V6, and V8, so I assume the weight difference is irrelevant. I would like to go with a 5.7 (350 ci.). I have already upgraded the prop to 2 degree over stock, so maybe it is sufficient, what do you think? My next question is, what is easier and more cost efficient to do, change the gearing in the current drive or get a drive that was on a V8 to begin with?

 

The 5.7 is pretty close to the limit of what the Alpha can comfortably handle. (Details, http://www.mercurymarine.com/mercury_mercruiser ) The 5.7/Alpha combination is often OK as long as the boat is fairly light and isn't run hard or full-out very often. If you frequently run with a lot of people and like lots of speed, the Bravo 1 or 3 would be a more reliable drive under the bigger loads.