3.7 to 4.3 swap

[Dubed]

Hey guys.
I'm tossing around the idea of losing my 3.7 190 and installing a 4.3 in my Chris Craft Scorpion 211 VF.
I know I have seen this conversation before but would like to start with the engine mount stringers.
1st pic is the empty engine bay in mine (note the stringers).
2nd pic is a picture I found online of an identical boat with a 4.3. (looks to be the same)
Can I assume this boat has the correct stringers already? I believe it came originally with 2 options, the 3.7 and I thought it was a V8 230 hp. Interested in the V6 because supposedly it bolts to my Alpha one.
What else would be needed to do the swap? I assume wire harness and....?

I've had this boat since 2008 and just tired of fighting with the 3.7 and all its problems (so just in the thinking about it mode)

 

[Scott Danforth]

Hey @nola mike , can you share links to your conversion

 

[nola mike]

Nola Mike's 3.7/470 --> 4.3L swap thread

I'm sure that this will be a saga, so starting a new thread. Just picked up an '89 Glastron donor with a 4.3. I'm planning on refurbing the engine and adding a 4bbl carb and vortec heads. I'm going to start on the engine in a bit, and then swap it in the fall after the season. 1st question...

forums.iboats.com

You'll need to glass in mounts, you don't have what you need there. Don't know how much your boat weighs, but might consider a 5.7. You can use the alpha if you have a light right hand. You don't need wire harness; what you need depends on your donor. You *will* need a junked donor boat, don't try to piecemeal it.

 

[Dubed]

Nola Mike's 3.7/470 --> 4.3L swap thread

I'm sure that this will be a saga, so starting a new thread. Just picked up an '89 Glastron donor with a 4.3. I'm planning on refurbing the engine and adding a 4bbl carb and vortec heads. I'm going to start on the engine in a bit, and then swap it in the fall after the season. 1st question...

forums.iboats.com

You'll need to glass in mounts, you don't have what you need there. Don't know how much your boat weighs, but might consider a 5.7. You can use the alpha if you have a light right hand. You don't need wire harness; what you need depends on your donor. You *will* need a junked donor boat, don't try to piecemeal it.

I realize the mounts aren't there and need to be glassed in. The V8 230hp was an option so u was thinking the engine bay was set up for either option. Does that make sense?
And thank you!

 

[Dubed]

Nola Mike's 3.7/470 --> 4.3L swap thread

I'm sure that this will be a saga, so starting a new thread. Just picked up an '89 Glastron donor with a 4.3. I'm planning on refurbing the engine and adding a 4bbl carb and vortec heads. I'm going to start on the engine in a bit, and then swap it in the fall after the season. 1st question...

forums.iboats.com

You'll need to glass in mounts, you don't have what you need there. Don't know how much your boat weighs, but might consider a 5.7. You can use the alpha if you have a light right hand. You don't need wire harness; what you need depends on your donor. You *will* need a junked donor boat, don't try to piecemeal it.

And I believe the boat weighs around 2500 lbs without the engine. I don't think they offered a 6 cylinder back then because not enough ponies

 

[Bondo]

I realize the mounts aren't there and need to be glassed in. The V8 230hp was an option so u was thinking the engine bay was set up for either option. Does that make sense?
And thank you!

Ayuh,...... The 5.7l is the same size as the 305,...... For the effort, go Big,.....

I think it's only 4" or so, 'tween the V6, 'n V8 glassed mounts,.....

 

[Scott06]

Hey guys.
I'm tossing around the idea of losing my 3.7 190 and installing a 4.3 in my Chris Craft Scorpion 211 VF.
I know I have seen this conversation before but would like to start with the engine mount stringers.
1st pic is the empty engine bay in mine (note the stringers).
2nd pic is a picture I found online of an identical boat with a 4.3. (looks to be the same)
Can I assume this boat has the correct stringers already? I believe it came originally with 2 options, the 3.7 and I thought it was a V8 230 hp. Interested in the V6 because supposedly it bolts to my Alpha one.
What else would be needed to do the swap? I assume wire harness and....?

I've had this boat since 2008 and just tired of fighting with the 3.7 and all its problems (so just in the thinking about it mode)

If boat was offered with a V8 i would bet those stringers are for v engine mounts. Here is a 5.7 install drawing measure it up iff the gimbal bearing as crankshaft center line

https://samerwebapp01apncus01.azureedge.net/mmgw-env-b/filer_public/50/c1/50c13579-9b83-41bb-90c9-f0958ee21906/57lalpha_1996-2001.pdf

Here is a 4.3 drawing mounts are 4” further back on the sides.https://samerwebapp01apncus01.azureedge.net/mmgw-env-b/filer_public/a6/0e/a60edabe-830a-4a0e-af7c-d296ce044500/43lhalphawithtwo-pieceexhaustmanifold_1996-2001.pdf

for a 21 ft boat id go with a 5.7. Your drive will fit up just has the wrong gear ratio. I did a 4.3 to 5.0 swap kept the V6 drive ratio stepped up from a 19” to 21” pitch prop works great. Given what you lay out i would expect to have to go up 4” in pitch if you kept the same drive. Worst case get a correct ratio upper drive.
In the end i was fearful of drive ratio issue so i stayed with a 5.0 (biggest factory offered in my boat) instead of a 5.7…knowing what i know now i wish i had listened to folks and done a 5.7 probably would have been fine with a 23” pitch prop or i just could have swapped the drive upper…live and learn…

 

[QBhoy]

Only engine that will drop straight in without fuss, is a 3.0. Anything with a v needs plenty of messing.

 

[Dubed]

Only engine that will drop straight in without fuss, is a 3.0. Anything with a v needs plenty of messing.

Yep I get that.
Not enough ponies, won't push this boat

 

[QBhoy]

Yep I get that.
Not enough ponies, won't push this boat

I’m sure it would plane her no bother. But if you’re after going fast…bypass the 4.3 and go v8. No reason not to, I suppose.
I’ve been familiar with a few attempts at nursing a 3.7 in a friends 23ft 4 berth cruiser…he eventually put a 3.0 in her. Was only a second or two slower to plane and only noticed 1 mph less top end. Still managed early 30’s mph no problem

 

[Dubed]

I’m sure it would plane her no bother. But if you’re after going fast…bypass the 4.3 and go v8. No reason not to, I suppose.
I’ve been familiar with a few attempts at nursing a 3.7 in a friends 23ft 4 berth cruiser…he eventually put a 3.0 in her. Was only a second or two slower to plane and only noticed 1 mph less top end. Still managed early 30’s mph no problem

Really? That's hard to imagine. Doesn't the 3.0 only push out 130 hp? And I thought it was pretty weak in the torque dept?

 

[QBhoy]

Really? That's hard to imagine. Doesn't the 3.0 only push out 130 hp? And I thought it was pretty weak in the torque dept?

Yeah. No doubt the 3.7 had more punch low down…it had 170hp. The 3.0 he put in was 135hp at the flywheel. I suspect the 3.7 figures are varied. Mercury rated prop hp when the 3.7 was around, mostly…I’m sure. The 3.0 would certainly be lighter too.
The boat I refer to was a 7 metre darragh cruiser. Had an alpha gen 1. Both engines used a 17” prop well.

 

[Rick Stephens]

Fun project. I went from a 3.0L to a 4.3L. Same scale as you going from your 3.7 to a 5.7L. I'd go the 5.7 in a heartbeat. 2 barrel carb and nothing fancy and your boat jumps out of the water and is as fuel efficient as a 5.7 can get. Find a donor boat.

 

[achris]

Years ago I went from an old 165 (same width as your 3 litre) to a 4.3 (same width as a V8). A bit of fiddling around. Had to modify the transom cutout slightly, and cut away some floor to glass in new mounts, widen the engine cover... Don't regret it for a second!

Just as an aside. You don't need a V8, 4.3 litre V6 will give you plenty of 'go'. My old 4.3LX got dropped into a 23' Caribbean Crusader, and it topped out at 36 knots! The previous engine in that boat was a 5 litre V8, which only ever got it to 30 knots...

Chris...

 

[Lou C]

Given the high fuel prices of this year I’m liking my old 4.3 with the Quadrajet 4bbl. The small primaries make it very economical.

 

[jimmbo]

Ayuh,...... The 5.7l is the same size as the 305,...... For the effort, go Big,.....

I think it's only 4" or so, 'tween the V6, 'n V8 glassed mounts,.....

I agree, with Bondo. Nothing Less than a 5.7 in 21 footer. It is less likely to take forever to get on plane, and it will have a Higher Top End which is always nice if you have to get somewhere in a hurry, or away from a Storm

 

[achris]

.... Nothing Less than a 5.7 in 21 footer....

Bollocks! 4.3 propped right is plenty good enough. And with the want of passengers to head aft, you'll be grateful not carrying that extra 100kg!

 

[Dubed]

Nola Mike's 3.7/470 --> 4.3L swap thread

I'm sure that this will be a saga, so starting a new thread. Just picked up an '89 Glastron donor with a 4.3. I'm planning on refurbing the engine and adding a 4bbl carb and vortec heads. I'm going to start on the engine in a bit, and then swap it in the fall after the season. 1st question...

forums.iboats.com

You'll need to glass in mounts, you don't have what you need there. Don't know how much your boat weighs, but might consider a 5.7. You can use the alpha if you have a light right hand. You don't need wire harness; what you need depends on your donor. You *will* need a junked donor boat, don't try to piecemeal it.

Wow! I was reading your thread last night. Quite the journey you recoerded there. Thank you for sharing. There a lot of hands on info there.

 

[Dubed]

Thanks everyone for your guidance.
I guess the big decision would be 4.3 or 5.7. I cant imagine why a 4.3 wouldn't be a good choice, take up less room for easier maintenance and a bit lighter.
Given that a 190 hp 3.7 pushes the boat fine (would like a bit more when hauling 4 people and gear however) I am happy with the performance of the boat. Once on plane, I bring her up to 3200 - 3400 rpm and she does between 24 and 30 mph which is comfortable if its not too rough.

If I decide on a 4.3, any particular year or model range I should look for? If I get a donor boat, I would probably have to rebuild or replace motor and or outdrive. I have 2 outdrives for my boat now with the 1:84 ratio so another reason to stick with 4.3

 

[Scott Danforth]

If I decide on a 4.3, any particular year or model range I should look for? If I get a donor boat, I would probably have to rebuild or replace motor and or outdrive. I have 2 outdrives for my boat now with the 1:84 ratio so another reason to stick with 4.3

post 1996