engine swaps

[vincechig1975]

I was wondering if it might be possible to swap a 3.7l out for a 4.3l and what year of engine should I look for and are there any issues I need to be aware of before doing so?

 

[solar7647]

Re: engine swaps

Yes it's possible, they take the same out drive as long as the 3.7l is an alpha 1 and the 4.3l is to. It does require a new transom assembly to be correct. The only difference between the transom for a 4cyl and a v6 is the mounting plate for the exhaust because the bolt pattern is different. A v6 requires a y pipe witch mounts with four bolts in a rectangle pattern to the transom assembly but a 4cyl bolt pattern has what would be the bottom left corner of the rectangle pattern moved up......Now you can mate a v6 y pipe to a 4cyl transom mount but that bottom corner bolt for the exhaust y pipe will not line up.

I did the same swap last year, I pulled my 87 3.7 and dropped in a 87 4.3 205. I had to build and install mounting pedestals because the 3.7 mounts from the front and the 4.3 mounts from the side. I used the same transom assembly and drive since its the same gear ratio for both engines and just installed the y pipe with three bolts instead of four and had a great season......now I can't go tell you to do it since it is not the correct set up, but if your like me and trust your ability you can make it work. But again to make it spec it does require a new transom assembly, but the alpha 1 3.7 and the 4.3 have the same drive as a standard witch is the 1.84:1 ratieo.

 

[Don S]

Re: engine swaps

Anything's possible with enough money, enough work, and enough time.

A V6 is not a direct bolt in, exhaust is different, overall size is different, mounting is different. Nothing from the 470 is usable.

 

[achris]

Re: engine swaps

Hey Solar... I remember you doing the 470 rebuild. Sweeeeeeet.... Loved the paint job... That engine gone now?

Anyway, I did a search and the gimbal housing (transom assembly) from 1983-on is the same for in-line and V engines. If you couldn't see the last bolt hole it may have been clogged up with dirt. It will be there somewhere ....

Cheers,

Chris.......

 

[Fishermark]

Re: engine swaps

They are not the same, as you can see from the picture below. But what I find interesting, is that Mercruiser is okay with using either one. The transom assembly I have pictured below came from my late eighties vintage Sportcraft. It came from the factory with a 5 liter Mercruiser and Alpha 1. When I replaced the original engine and Y Pipe, I saw that the transom assembly that was used was for an inline engine. I asked Mercruiser about it and they replied that their engineers had decided that it was okay to use either way - even though the fourth bolt doesn't line up!

One last thing - if my memory serves - isn't there a fifth bolt "hidden" in the center - at the top of the "u" shaped channel as well?

 

[solar7647]

Re: engine swaps

Hey Solar... I remember you doing the 470 rebuild. Sweeeeeeet.... Loved the paint job... That engine gone now?

Anyway, I did a search and the gimbal housing (transom assembly) from 1983-on is the same for in-line and V engines. If you couldn't see the last bolt hole it may have been clogged up with dirt. It will be there somewhere ....

Cheers,

Chris.......

yea i did do the 3.7L rebuild, i did the swap because the 4.3L was free and with the increased use of the boat and ease of getting 4.3 parts it was just smarter and gave me peice of mind. With that 3.7L even though it was running great i always had the voice in the back of my head that told me to take it easy cause if something breaks it could take weeks to get a replacement. So i pulled it and sold it and pocked some serious cash! Used about 300 bucks of the cash i made to do an over haul of the 4.3 getting it cleaned and replaceing a few little parts because of rust and never looked back...and its been running like a dream.

And i am not sure were you looked but there is a differance between a 4cyl and V6/v8 transome assemble bolt pattern, you can see it in manual 6.

 

[achris]

Re: engine swaps

...And i am not sure were you looked but there is a differance between a 4cyl and V6/v8 transome assemble bolt pattern, you can see it in manual 6.

I checked in Merc's Electronic Parts Catalogue For R, MR, Alpha One they have one gimbal housing listed, no notes or anything about being different between the 4s an 6/8s. I looked in the manual and agree with you, they do show that they are different....

Chris......

 

[vincechig1975]

Re: engine swaps

I will look into this further, have any links to follow, or maybe send my way to see the differences? I would like to stay in touch as I progress to the final decision of which to us the four or the six. Have you noticed any increases in h.p., handling of the boat ?

 

[solar7647]

Re: engine swaps

I will look into this further, have any links to follow, or maybe send my way to see the differences? I would like to stay in touch as I progress to the final decision of which to us the four or the six. Have you noticed any increases in h.p., handling of the boat ?

My 3.7l was 180 hp the 4.3l I got is the 262 ci 205hp with a 4 bal carb. The 4.3l starts at 175hp I believe depending on the year, the cylinder size changed but I am not sure what year it changed so when looking you will need to look out for that because the Hp rating can go up to 225hp if it's the 262 ci and fuel injected.

I have noticed a few differences the first is the 4.3l is heavier so I noticed the boat displaces more water but I do a lot of wakeboarding so the bigger wake is welcome. The boat planes a lot faster expacialy when doing water sports with a full boat of people and gear. It seems to be more stable in the water as well, I think it's because of the additional weight. I got a small increase in top speed but not much since the drive is the same and the 4.3l has the same WOT rpm as the 3.7l this will most likely change next season, my currant drive is 1:94/1 gear ratio so I will be installing the proper 1:84/1 drive. The best thing is its a lot quiter and doesn't vibrate the boat like the 3.7l.

I really don't know of any links or anything to help you but I can tell you that installing a 4.3l will require fiberglass work to install the side pedistles for the motor mounts. It's kinda tricky to do, I used an overhead gantry to lower the engine in place on the transom mount and leveled it up and took all the needed measurements and then removed it and glassed in the pedestals. You will also have to allign the engine but that will need done regardless of the engine you put in. I would say get manuals 6 witch is for the drive, manual 7 witch is for the 4.3l and manual 8 witch is for the 3.7l. Then use them as your references. Like I said before, the only thing that didn't match up was the exhaust hook up, the bolt pattern for the 4cyl is different from the 6cyl but the 6cyl y pipe will seal on the 4cyl bell housing you just only use three bolts instead of 4.

It's a project so do your home work and if your not confident in your mechanical skills I wouldn't try it.

 

[vincechig1975]

Re: engine swaps

Thankyou for the input advise and information, I am hoping to find the 6 after the new year, and begin the installation in the spring as long as time and monies hold out for us. Would a long block work out of a standard rotation blazer/s10? I read somewhere on here about it and was curious?

 

[solar7647]

Re: engine swaps

I believe the only difference in the long block would be the cam size, but it shouldn't make a difference. But remember nothing from the 3.7 can transplant to the 4.3 so you need a bad doner engine or your going to need to buy a lot of parts. I would surf eBay, or even CL but eBay is prolly the better choice. you can find a used drop in ready used 4.3 for a good price.