I'll just start out by saying unless you are infatuated with the boat and can't stand to replace it, you are much better off looking for the same boat with the power you want. Mine being an 84, there are few and far between that are still this clean and would have the power I want. So enter my insanity and swapping engines. I went from a 3.0l to a 4.3l.
The job really isn't bad if a few chance things line up. First, my boat was available from the factory with power up to a 350 MAG. So the bilge was already able to accommodate it. I took a bunch of measurements and compared them to the Mercruiser dimensional drawings to make sure I'd have the room. The dog house fit fine, the only modification that had to be made was my back trim panel had to be widened for the manifolds and elbows. Peel back vinyl and trim plywood. Nothing crazy.
Once I confirmed it would fit, I found a engine and all accessories. You need at a minimum the complete engine, Y-pipe, and drive for your transom assembly. I retained my original Alpha 1 assembly as he had a decent drive. I decided to delete power steering for now at the time, the pump that was on the engine had a front seal weep and I didn't want to deal with that mess. If I felt it needed power steering, I could easily add it back. Just so we're all clear, I am not adding it back, it is perfectly manageable without. Also saves a couple pounds on the ass end. I also decided to replace the input yolk seal on the new drive as it probably wouldn’t be a bad idea. I actually ended up swapping my lower onto the correct ratio upper as the one included was pretty beat up and mine was... well... pretty nice. I was hoping to not have to do that as my lower is a preload pin one. I do have a near perfect alpha 1 case in the garage that I will eventually build for this boat. This was the easier route for now.
So now the actual swap could begin since I had the engine, drive and exhaust figured out. First step was to pull the 3.0l and drive. I ended up reusing my entire transom assembly as there was no real need to swap it. Now the actual “swap” work began. From the day I pulled the engine to the bay test with the 4.3l was about 10 days. And that was only working on my days off. It was a total of 4 working days if that. Maybe 20 hours of labor. Now I’m not saying it was easy, it’s just that this kind of work isn’t something I’m unfamiliar with so most of the leg work was done measuring out and prepping prior to pulling the engine or obtaining a 4.3l. So once everything was confirmed to fit, I measured out and glassed in engine mounts and notched the stringers to fit the Y-pipe.
I hadn’t found this out until I was about to drop the engine in, but the stringers were a little too narrow to allow the Y-pipe to fit in on the transom. Dad’s knee jerk response to that was “dual 4” straight out the back.” To which I stared at him and he just laughed. So we notched and glassed out the top inch of the rear of the stringers so it would drop down the rest of the way. I came to later find out looking at photos of the same boat with V8 power that they stepped down the stringer for clearance on the V powered boats for the last 6 inches.
The last day was spent making all the wiring checked out, I actually replaced my ignition plug as the original to the boat had rotted out many years ago and all the wiring was hard wired. It is nice having the plug on top of the engine that you can just disconnect if you need to pull it.
The following day we went for a bay test. Originally I was extremely disappointed. Boat picked up maybe 1 MPH at cruise and only 1 MPH up top. I was not in a good place. Then I got thinking... this was a thunderbolt V ignition. What are the chances that this guy didn’t set base timing correct? Lucky me that was the case. It had 2 degrees of retard instead of the recommended 10 degrees BTDC in base timing. So I figure at wide open I was missing some 13 degrees of initial advance. Boat picked up 6 MPH up top with that one adjustment, which is more what I would expect.
So, the before and after? With the 3.0l she would top out 36-37 MPH on the best of days atmosphere wise but typically was all in at 35 MPH on most days. Cruise was 23-24 MPH at 3000-3200 RPM. I tend to run out with dad a lot and his 330 cruises near 30 MPH. So to keep up with him I was always running it hard wherever we went, needed to run 3800 RPM to do those speeds and those 3.0s aren’t exactly quiet at those speeds. Now with the 4.3l cruise is 29 MPH at 3300 RPM and it tops out at 44 MPH on good atmosphere days, 42-43 MPH on all others. I’ve found doing the rough math that my best overall range is to actually run 3700 RPM at about 35 MPH. The hull and everything handling wise feels awesome in that 32-35 MPH slot. And my fuel use for anything between 28-35 MPH nets me about the same distance traveled. Obviously filling up after running a whole tank at that speed isn’t perfect but it gets close enough for decent judgment.
The two biggest things I can take away from this swap is this: for how much quieter it is alone it was worth the cost. And the fact it hops on plane with 5 guys in the boat faster than the 3.0l did with just me and a quarter tank is completely worth it too. Is fuel consumption higher? Yes. But I am getting everywhere significantly quicker so over the whole days outing, it really ends up being a near wash. I do however think I will be adding the optional larger tank the boat could have come with as 20 gallons of usable fuel, even with the 3.0l, went very quick. Having 32 gallons I can use will be a nice addition this winter along with the other work to be done. My math on the 3.0l always put me around 4.2 MPG or ~5.5 gallons per hour at cruise. Currently I am seeing about 4.0 MPG at cruise or about 7.4 GPH. That is also 23 vs ~31 MPH. It takes me just under an hour to reach my usual spot now where it used to take almost an hour and a half prior. So over that same distance I was using nearly the same 7 gallons. This isn’t for everyone.
For me, the swap was 100% worth it. Hell, I may look into a 4 barrel conversion and see if I can snag a little more top end come next season. I may also try a 21p prop as I should still be able to swing 4600-4700 RPM loaded. The 3.0l always put up better numbers with wide open 45-4600 than 4800 which is why I kept the 19p. As long as I am getting into the proper WOT range with the 21p I'll leave it alone for just me.
It did suck the used “fresh rebuild” ended up being a dud but now I have an engine I 100% can trust for years to come. (you can see my popped through the intake thread for that journey...) Now for the overall cost? Well... lets just call it $8000. That includes the rebuild and all the miscellaneous parts involved in the swap plus replacing the “new” GLM manifolds that leaked that came with the engine originally with a new set of OE mercruiser ones. That also includes the original purchase price of the 4.3l and extra transom assembly, power steering and drive... Cheaper than new but when it was all said and done an alpha 4v 4.3l is $9500. Finding a boat in as good of shape that I actually like with the power I want would’ve been around $20,000. So I am ahead. But this is not for everyone. I am very happy. I will also add that we repowered to the 3.0l in 2003 for about $2200. We put over 700 trouble free hours on that engine. I pulled it out and listed it for sale just to see what would happen... guy offered $1500. That was a great investment in my book.
I'll also add, last weekend I was out and blew past my friend. He called me and thought I was running balls out but was just cruising around 33. His exact words were "I can't believe how much of the boat is out of the water, it looks really cool like that." I am looking forward to next season.
The job really isn't bad if a few chance things line up. First, my boat was available from the factory with power up to a 350 MAG. So the bilge was already able to accommodate it. I took a bunch of measurements and compared them to the Mercruiser dimensional drawings to make sure I'd have the room. The dog house fit fine, the only modification that had to be made was my back trim panel had to be widened for the manifolds and elbows. Peel back vinyl and trim plywood. Nothing crazy.
Once I confirmed it would fit, I found a engine and all accessories. You need at a minimum the complete engine, Y-pipe, and drive for your transom assembly. I retained my original Alpha 1 assembly as he had a decent drive. I decided to delete power steering for now at the time, the pump that was on the engine had a front seal weep and I didn't want to deal with that mess. If I felt it needed power steering, I could easily add it back. Just so we're all clear, I am not adding it back, it is perfectly manageable without. Also saves a couple pounds on the ass end. I also decided to replace the input yolk seal on the new drive as it probably wouldn’t be a bad idea. I actually ended up swapping my lower onto the correct ratio upper as the one included was pretty beat up and mine was... well... pretty nice. I was hoping to not have to do that as my lower is a preload pin one. I do have a near perfect alpha 1 case in the garage that I will eventually build for this boat. This was the easier route for now.
So now the actual swap could begin since I had the engine, drive and exhaust figured out. First step was to pull the 3.0l and drive. I ended up reusing my entire transom assembly as there was no real need to swap it. Now the actual “swap” work began. From the day I pulled the engine to the bay test with the 4.3l was about 10 days. And that was only working on my days off. It was a total of 4 working days if that. Maybe 20 hours of labor. Now I’m not saying it was easy, it’s just that this kind of work isn’t something I’m unfamiliar with so most of the leg work was done measuring out and prepping prior to pulling the engine or obtaining a 4.3l. So once everything was confirmed to fit, I measured out and glassed in engine mounts and notched the stringers to fit the Y-pipe.
I hadn’t found this out until I was about to drop the engine in, but the stringers were a little too narrow to allow the Y-pipe to fit in on the transom. Dad’s knee jerk response to that was “dual 4” straight out the back.” To which I stared at him and he just laughed. So we notched and glassed out the top inch of the rear of the stringers so it would drop down the rest of the way. I came to later find out looking at photos of the same boat with V8 power that they stepped down the stringer for clearance on the V powered boats for the last 6 inches.
The last day was spent making all the wiring checked out, I actually replaced my ignition plug as the original to the boat had rotted out many years ago and all the wiring was hard wired. It is nice having the plug on top of the engine that you can just disconnect if you need to pull it.
The following day we went for a bay test. Originally I was extremely disappointed. Boat picked up maybe 1 MPH at cruise and only 1 MPH up top. I was not in a good place. Then I got thinking... this was a thunderbolt V ignition. What are the chances that this guy didn’t set base timing correct? Lucky me that was the case. It had 2 degrees of retard instead of the recommended 10 degrees BTDC in base timing. So I figure at wide open I was missing some 13 degrees of initial advance. Boat picked up 6 MPH up top with that one adjustment, which is more what I would expect.
So, the before and after? With the 3.0l she would top out 36-37 MPH on the best of days atmosphere wise but typically was all in at 35 MPH on most days. Cruise was 23-24 MPH at 3000-3200 RPM. I tend to run out with dad a lot and his 330 cruises near 30 MPH. So to keep up with him I was always running it hard wherever we went, needed to run 3800 RPM to do those speeds and those 3.0s aren’t exactly quiet at those speeds. Now with the 4.3l cruise is 29 MPH at 3300 RPM and it tops out at 44 MPH on good atmosphere days, 42-43 MPH on all others. I’ve found doing the rough math that my best overall range is to actually run 3700 RPM at about 35 MPH. The hull and everything handling wise feels awesome in that 32-35 MPH slot. And my fuel use for anything between 28-35 MPH nets me about the same distance traveled. Obviously filling up after running a whole tank at that speed isn’t perfect but it gets close enough for decent judgment.
The two biggest things I can take away from this swap is this: for how much quieter it is alone it was worth the cost. And the fact it hops on plane with 5 guys in the boat faster than the 3.0l did with just me and a quarter tank is completely worth it too. Is fuel consumption higher? Yes. But I am getting everywhere significantly quicker so over the whole days outing, it really ends up being a near wash. I do however think I will be adding the optional larger tank the boat could have come with as 20 gallons of usable fuel, even with the 3.0l, went very quick. Having 32 gallons I can use will be a nice addition this winter along with the other work to be done. My math on the 3.0l always put me around 4.2 MPG or ~5.5 gallons per hour at cruise. Currently I am seeing about 4.0 MPG at cruise or about 7.4 GPH. That is also 23 vs ~31 MPH. It takes me just under an hour to reach my usual spot now where it used to take almost an hour and a half prior. So over that same distance I was using nearly the same 7 gallons. This isn’t for everyone.
For me, the swap was 100% worth it. Hell, I may look into a 4 barrel conversion and see if I can snag a little more top end come next season. I may also try a 21p prop as I should still be able to swing 4600-4700 RPM loaded. The 3.0l always put up better numbers with wide open 45-4600 than 4800 which is why I kept the 19p. As long as I am getting into the proper WOT range with the 21p I'll leave it alone for just me.
It did suck the used “fresh rebuild” ended up being a dud but now I have an engine I 100% can trust for years to come. (you can see my popped through the intake thread for that journey...) Now for the overall cost? Well... lets just call it $8000. That includes the rebuild and all the miscellaneous parts involved in the swap plus replacing the “new” GLM manifolds that leaked that came with the engine originally with a new set of OE mercruiser ones. That also includes the original purchase price of the 4.3l and extra transom assembly, power steering and drive... Cheaper than new but when it was all said and done an alpha 4v 4.3l is $9500. Finding a boat in as good of shape that I actually like with the power I want would’ve been around $20,000. So I am ahead. But this is not for everyone. I am very happy. I will also add that we repowered to the 3.0l in 2003 for about $2200. We put over 700 trouble free hours on that engine. I pulled it out and listed it for sale just to see what would happen... guy offered $1500. That was a great investment in my book.
I'll also add, last weekend I was out and blew past my friend. He called me and thought I was running balls out but was just cruising around 33. His exact words were "I can't believe how much of the boat is out of the water, it looks really cool like that." I am looking forward to next season.
