5.7 to 3.7 swap. Possible?

walleyejunkie889 · Jan 28, 2012

I have a 21ft Lund sportcabin with a 5.7 that is way overpowered. I found a donor motor and outdrive plus any extra parts off the old boat if needed. Is this swap possible? What's involved? Motors are almost the same years. First post!

Bondo · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

walleyejunkie889 said:
I have a 21ft Lund sportcabin with a 5.7 that is way overpowered. I found a donor motor and outdrive plus any extra parts off the old boat if needed. Is this swap possible? What's involved? Motors are almost the same years. First post!

Ayuh,.... Welcome Aboard,.... That'll be the Quickest way to ruin a perfectly good boat....

Do a search of this forum for info on the imfomas 470 Mercruiser....
It's an antique motor no longer supported by Merc...

A 4.3l would be a Much Better way to go...

Silvertip · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

So it's overpopwered! Boats have a throttle lever. Just because it's there doesn't mean it needs to be wide open. Throttle back, enjoy the ride and spend zero money on an unnecessary swap. Even if the current engine is junk, replace it with another 5.7 or 5.0. It will still be cheaper and more reliable than what you are proposing.

littlebookworm · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

What makes you think it's over-powered? No manufacturer would put a larger engine in a consumer boat than the boat could handle. That would be irresponsible. Tune up your engine, pull back on your throttle if you can't handle the power, and enjoy your ride. Don't ruin a good boat by installing a lousy engine. Hy

walleyejunkie889 · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

My reason for swapping is my outdrive needs torn down and re sealed. The motor was never winterized. And it doesn't shift properly. I don't know where to start and was quoted over 1500 for labor!

Bondo · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

and was quoted over 1500 for labor!

Ayuh,.... swappin' in a 470 won't change the labor bill.... 'n it's still a Major step backwards....

Get yerself a toolbox full a wrenches, 'n We'll walk ya through whatever needs doin'....

How 'bout some History on the boat,..??...

LilRedNeckGirl · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

Look at the new stern drives on Stern Drive engenering's web site. They may even sell them here in the marine store. They are affordable, brand new American Made, come with a huge and awesome warranty, and are direct bolt ups for mercruiser replacment.

Don S · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

iboats does sell the SEI drive, you just can't tell it. Scroll up to the top of this page, click on distorted drive that says Mercruiser Boat Motor and click on the Alpha Replacement Drive Assemblies link and follow the prompts. It doesn't say it, but it is SEI drives.

riskibusiness · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

OVERPOWERED!!!! OVERPOWERED!!!! Are we speaking English? Can a boat be overpowered? All kidding aside I am a 470 lover and I wouldn't even swap one in where you have a easy to maintain Chevy motor. The 3.7 is a pain in the *** and not for the faint hearted. It takes dedication to keep one of these on the water. Don't get me wrong all boats are expensive but why add extra expense and problems by deliberately introducing one into a perfectly good boat

Scott Danforth · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

BOAT is an acronym for Break Out Another Thousand.

welcome to Iboats. However I have to agree with everyone. swapping from a 5.7 to a 470 would be a major step backwards and probably cost you more than just fixing your existing drives.

vincechig1975 · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

Bondo, I was wondering something with that 3.7 in mind......my 3.7l is still a good running motor, would replacing it with a 4.3l be a possibility? and if so what would I need in order to make the swap? Now I am aware of the issue of exhaust but the parts needed to make that swap such as exh mans, intake and carb where and how much more cost wise would I be lookin at , figuratively speaking that is? I realize it is possible to make the swap but it's the extra cost and amount of parts to make it right. I currently have an Alpha 1 Gen 2 out drive and would like to stay with it. Lemme know your thoughts on it.

Pete104 · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

How do you have a Gen II behind a 3.7?
Figuratively speaking, your engine bed won't fit a V-6!

riskibusiness · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

If I remember correctly the 3.7 block is longer than the 4.3. So I would think that alone would be a problem. But I have seen guys put a 2x6 or something similar to it across the front but I don't know how safe that is????

walleyejunkie889 · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

Well this is my first I/O so I'm hesitant. It currently sits outside. I don't know the first thing about working on a sterndrive. I'd love to learn but I'm afraid to screw it up!

Pete104 · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

How about posting some pics? Serial numbers too!

26aftcab454 · Jan 28, 2012

Re: 5.7 to 3.7 swap. Possible?

walleyejunkie889 said:
Well this is my first I/O so I'm hesitant. It currently sits outside. I don't know the first thing about working on a sterndrive. I'd love to learn but I'm afraid to screw it up!

forget making major design changes and get what you have to function as intended.
The thing has a throttle ! stay under 3000 rpms and it will last forever.
These motors & drives are the least inexpensive way to go.

Scott Danforth · Jan 29, 2012

Re: 5.7 to 3.7 swap. Possible?

walleyejunkie889 said:
Well this is my first I/O so I'm hesitant. It currently sits outside. I don't know the first thing about working on a sterndrive. I'd love to learn but I'm afraid to screw it up!

Ask specific questions and go step by step.

if it was my boat, I would look at the following:

block never winterized. since your in Pennslvania - block and heads most likely toast. good thing is an SBC block and heads are a dime a dozen.
out drive needs to be sealed - is this a re-seal issue or did something freeze? (see above)
out drive doesnt shift - is it a shift cable, or is there something wrong with the outdrive?

these items beg another question. did you buy the boat as a project with these problems?

Bondo · Jan 29, 2012

Re: 5.7 to 3.7 swap. Possible?

these items beg another question. did you buy the boat as a project with these problems?

Ayuh,.... Which is why I asked for some History on the barge......

Bondo, I was wondering something with that 3.7 in mind.....

vincechig1975 ask in yer own thread,.... This 1 ain't yer's....

haulnazz15 · Jan 30, 2012

Re: 5.7 to 3.7 swap. Possible?

You would be out of your mind to swap a 5.7 to the 3.7. Heck, I wouldn't swap in a 4.3L either unless I just happened to have a spare one lying around and didn't plan on keeping the boat long. Putting in a new long block 5.7L (assuming your current engine is cracked) is going to be the cheapest option, no matter what. There is no conversion or other mess to deal with. I think you should have the engine looked at by a certified marine mechanic to get a diagnosis on the engine's condition (pressure test, compression test, etc), then make a decision.

5.7 to 3.7 swap. Possible?

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