3.0 conversion to v6 or v8, 1984 Glastron Conroy

[Christopher87glenn]

Hi all, new to boating, ive had this boat a few months and totally love it.. the interioir and gel are less then a year old so boat is pristine cosmetically.. the women opted for the prettiest boat which of course came with the 3.0 mercruiser. Engine was not overhauled and isnt the prettiest but runs great.. while researching gimbal bearing and bellow replacement that i recently did i noticed a lot of people have put 4.3, 5.0 and 5.7 engines in the same boat (of course they adjusted the ratio in the outdrives to ensure propper prop speeds) my question is who else has done this? Im a locomotive diesel mechanic by trade but a jack of all trades master of none so im not afraid of the callenge but i have big ears and i can listen.. i was going along the lines of a working order "donor" boat to swap for my HP.. any pointers or knowledge would be greatly appreciated.. alpha one gen one out.. im looking for any economical mechnical advice i can get. Thank you.

 

[Scott Danforth]

my advice to you, since you are new to boating

start with using your existing boat for a few years prior to swapping motors.

you will find that you will want to sell your boat for something bigger. that is when you buy a boat with the motor you want.

 

[nola mike]

Curious what model you have? Why are you swapping? Disagree that it isn't worth putting in a new fresh engine if you like the boat, but would agree that you run it for a while to see if the boat suits you. I'm looking at the same choice. Decided to redo my floors and interior, and am going to swap in a 4.3 at some point. I briefly thought about a v8 (why would you put in a 5.0?), but didn't want the weight penalty. The v6 is already going to be adding a couple of hundred pounds.

 

[achris]

If you really like the boat and want to do the upgrade, then as it's a 1984, then apart from 2 x 1/2" holes to be drilled (pretty sure they are 1/2"), any power package from 1983 until now will drop in.

There will be a bit of work to do though...

The cheapest way. I would find a donor boat with a good working drive and a cracked engine block (someone didn't drain it for winter properly and it cracked from freezing), no more than about 15 years old.. Get a similar engine from a truck and do the engine rebuild like that. That will give you the transom assembly, and drive, and a fresh engine.

Next option. Find a donor boat with a good working engine and drive (again, no more than about 15 years old), just swap it all out. Or a good engine and dead drive and put a new SEI drive on.

Next option. Find an engine from 1983 to 1991, drop that in and get an SEI drive of the appropriate ratio. That lets you keep the existing transom assembly in, but means a much older engine. That would be my least prefered option.

Ok, work you'll need to do to prepare the hull for the vee engine.
If the engine box isn't wide enough, it will need to be widened. The minimum width required is about 770mm.
The 3 litres has a front engine mount and the vees have side mounts. You may need to cut the floor for the side engine mounts. . You'll need to fabricate those too.

23 years ago I changed from an inline to a vee engine... GREAT move!

Anyway, plenty to think about, have fun.

Chris........

.... I briefly thought about a v8 (why would you put in a 5.0?), but didn't want the weight penalty. The v6 is already going to be adding a couple of hundred pounds.

The V6 will add 123kg (270lb) and the V8 will add about 185kg (407lb).... (from a 3 litre)

 

[stonyloam]

Well the v6 will add about 200#, the v8 about 400#. So it depends a little on how big your boat is. If a 17' I would stick with the 3.0. A larger boat, say 19' should handle the v6 no problem. I agree with the others, use it for a year and then decide.

 

[nola mike]

Maybe he should upgrade to a 3.7?

 

[Rick Stephens]

I swapped. I found a donor boat for $1500 with what was supposed to be a newly rebuilt 4.3, but turned into a little bit of a re-rebuild since it had water in the brand new cylinders. Even with that extra expense, after I sold everything I could, from motor, to outdrive to transom assembly, to seats, etc, it ended up being about a wash financially to accomplish. I put in quite a bit of labor, of course, but that was fun.

What I got out of it:

*More horsies. That is amazing wonderousness, as it cruises now where it use to be at WOT on the 3.0L.

*MUCH MUCH quieter! You can talk in the boat. The admiral would get angry when I went over 20 MPH with the 3.0L. Sounded like I was trying to drag race. Now she hardly notices 32 MPH. That much quieter.

*Power steering. I like it.

*Newer Gen2 outdrive. Only really noticeable difference year to year is the impeller lasts a lot longer.

*Added power makes skiing mucho better. Pop, out of the water.


About the same fuel usage since I seldom go faster. My 3.0L was gonna need a rebuild as it was a bit long in the tooth. The 4.3 was cheaper to rebuild than the 3.0 would have been by a bunch. I let the guy who bought my running on blocks 3.0L look forward to rebuilding it. Told him it needed it, too. (note, I got $1200 for the 3.0L here in the PNW. Some places will have lower resale values, other places higher. But I suspect a nicely cared for 3.0 is worth over a grand dressed out and running nearly anywhere)

If you like tinkering, is a lot of fun. Gotta find the donor boat or it would be too spendy.

Rick

 

[Christopher87glenn]

Thank you everyone!! Yea totally afraid of the 400lbs for a V8 but figured if im in there and cut happy.. the V8 migh5 be feasable.. its a x-19.. defientlyleaning towards a V6 after the imput.. it is only a 19ft boat so i think going from 130hp to the V6 will be a huge power difference as is.. i seen the MPI V6 out 5here but they want 6700 turn key for one haha.. a donor boat is defiently the plan.. i would like to keep my drive and transom (i would re-gear it of course).. either way i would wait a year to do it because i do wanna enjoy the boat before i rip her heart out haha.. thank you so much for imput.. basically whatever the newest/cheapest powerplant and drive assmblies i can get from a donor is the route i will go.. crashed boats im guessing the best?

 

[Christopher87glenn]

Curious what model you have? Why are you swapping? Disagree that it isn't worth putting in a new fresh engine if you like the boat, but would agree that you run it for a while to see if the boat suits you. I'm looking at the same choice. Decided to redo my floors and interior, and am going to swap in a 4.3 at some point. I briefly thought about a v8 (why would you put in a 5.0?), but didn't want the weight penalty. The v6 is already going to be adding a couple of hundred pounds.

X19 just like yours but a 84.. the boat really is a beauty and the horse power gain is mostly why.. i would like to cruise at 35 with less rpms as well as power to pull.. i thought about the 3.7 but figired a 4.3 would be worth the effort and some day i could put the electeonic fuel injection on it and that would be 90HP then when i started.. question.. what props sizes and pitch do you run? I have a 15/15p and was thinking trying a 15/17p

 

[achris]

If you just want to go the 'engine only' route, Any 4.3 will fit. If you want MPI, start with that. Changing from a carb to marine MPI is very very expensive.

Ratios. In a 19' boat, you would be best to change from the current 1.98:1 drive to a 1.62:1... Reasoning there is that even propping up you'll need about 25" or even 27" to keep the revs in spec with the 1.98:1... You can just buy a 1.62:1 upper from iboats for $645. (http://www.boatmotors.com/motorparts/index.cgi?pid=7522&flag=2)

Current prop. What are your maximum revs now? Should be 4200-4600. If it's higher than 4600, then you could change up to the 17" pitch prop. If it's in the range, leave it where it is.

3.7... Last 3.7 was made in 1989, so even the last one is now 28 years old. Best advise if you're not familiar with them is to stay away...

Chris.......

 

[Scott Danforth]

I go back to see post #2

 

[Rick Stephens]

I go back to see post #2

Scott,

Hard to flat out say it is wrong to jump in with both feet and repower your boat. Depends on what the OP is wanting out of their boating. If like me, I wanted something to tinker with and feed my fishing habit. I've pretty much completely rebuilt, retasked and reconfigured a ski boat into a fishing barge with some ooomph. Didn't need to do any of it. Could a bought a tinny with an outboard and just gone fishing. But I got more than my monies worth fooling around in the shop all winter. Heck, I'm sitting at my desk making and remaking lures. Idle hands, devils and those kind of things, I guess.

I'll bet it didn't take long running that boat for the OP to dream about it with double the horsies. Up to him to decide whether it is better to scale up to a different boat or search out and start a donor boat project. Not arguing, your point is well taken: sell, buy and go boating. But it ain't wrong to make a project out of it for the projects sake.

Rick

 

[Scott Danforth]

my advise to first time boat owners is not to think about re-powering. especially a 33 year old boat. if after a year, the OP still loves the boat, then no problem.

Im one that loves projects, however for first time boater without boating experience, I say wait for the 2nd boat.

 

[nola mike]

I agree with scott's sentiment about waiting. I also was kidding about the 3.7. But it wouldn't hurt to start looking around either. My 3.7 actually has plenty of power for most things--1700# isn't a lot of weight to push, and I'm still touching 50 mph, even though it's a 30 yo engine. Only complaint is for skiing, and it has a real hard time pulling 185# out of the water on a short slalom ski. That's why I'd love the V6. 220 hp would scream in that thing. And a fresh engine install with a good hull/good interior is better than anything you'll get at the low price points we're talking about. The MPIs are prohibitively expensive, and I looked without success for an aftermarket marine FI system. FWIW, I run a 23p prop on my 1.84 drive, and a 25p on my 1.98. I can't notice a difference in performance between the 2. I don't know if I'd have enough prop left on the 1.84 to handle the V6.

 

[ondarvr]

I agree, wait and see exactly what you want before spending money on the current one. If it runs great now, it should for another year or so.

 

[Christopher87glenn]

If you just want to go the 'engine only' route, Any 4.3 will fit. If you want MPI, start with that. Changing from a carb to marine MPI is very very expensive.

Ratios. In a 19' boat, you would be best to change from the current 1.98:1 drive to a 1.62:1... Reasoning there is that even propping up you'll need about 25" or even 27" to keep the revs in spec with the 1.98:1... You can just buy a 1.62:1 upper from iboats for $645. (http://www.boatmotors.com/motorparts/index.cgi?pid=7522&flag=2)

Current prop. What are your maximum revs now? Should be 4200-4600. If it's higher than 4600, then you could change up to the 17" pitch prop. If it's in the range, leave it where it is.

3.7... Last 3.7 was made in 1989, so even the last one is now 28 years old. Best advise if you're not familiar with them is to stay away...

Chris.......

Thank you for the knowledge, yes i priced everything out and with a little more leg work and time on my side and proper connections i can repower for 1500 for a mpi 4.3 so thats the route im going.. so that ratio swap you were talking about doing that after i do the engine swap correct?? Cause i was planning on that.. or are you saying to swap it for more speed? My boat does rev over so i will try a 17p.. thank you so much for your time

 

[Christopher87glenn]

Scott,

Hard to flat out say it is wrong to jump in with both feet and repower your boat. Depends on what the OP is wanting out of their boating. If like me, I wanted something to tinker with and feed my fishing habit. I've pretty much completely rebuilt, retasked and reconfigured a ski boat into a fishing barge with some ooomph. Didn't need to do any of it. Could a bought a tinny with an outboard and just gone fishing. But I got more than my monies worth fooling around in the shop all winter. Heck, I'm sitting at my desk making and remaking lures. Idle hands, devils and those kind of things, I guess.

I'll bet it didn't take long running that boat for the OP to dream about it with double the horsies. Up to him to decide whether it is better to scale up to a different boat or search out and start a donor boat project. Not arguing, your point is well taken: sell, buy and go boating. But it ain't wrong to make a project out of it for the projects sake.

Rick

Haha yea a winter project.. and like i said the wife is IN LOVE with how pretty the boat is and has heart set on keeping it forever even though she knows what my next boat is.. she helped work for it and its pretty to her so i wanna make it fun for me.. she thinks its fast enough but like you said for projects sake and to stress her out a little haha

 

[Christopher87glenn]

my advise to first time boat owners is not to think about re-powering. especially a 33 year old boat. if after a year, the OP still loves the boat, then no problem.

Im one that loves projects, however for first time boater without boating experience, I say wait for the 2nd boat.

Your totally right sir.. shes old.. but the previous owner dumped way more then i would have into redoing everything brand new EXCEPT its heart haha.. i will take your advice and just have fun before i rip her open.. but next boat will be bought how i want it haha..

 

[Christopher87glenn]

I agree with scott's sentiment about waiting. I also was kidding about the 3.7. But it wouldn't hurt to start looking around either. My 3.7 actually has plenty of power for most things--1700# isn't a lot of weight to push, and I'm still touching 50 mph, even though it's a 30 yo engine. Only complaint is for skiing, and it has a real hard time pulling 185# out of the water on a short slalom ski. That's why I'd love the V6. 220 hp would scream in that thing. And a fresh engine install with a good hull/good interior is better than anything you'll get at the low price points we're talking about. The MPIs are prohibitively expensive, and I looked without success for an aftermarket marine FI system. FWIW, I run a 23p prop on my 1.84 drive, and a 25p on my 1.98. I can't notice a difference in performance between the 2. I don't know if I'd have enough prop left on the 1.84 to handle the V6.

You have two different drives you use? I think if i had the 3.7 i would be less into the idea of a repower but you def have about 30HP then me and your right with these little boats you would feel even 10hp.. so to go from a 3.0 which make "140" either at prop or crank (i dont know) to a 220 at the crank will just be rediclous..

The 4.3 is so much cheaper to rebuild and work on too.. even 1 year warranties available..

 

[achris]

Thank you for the knowledge, yes i priced everything out and with a little more leg work and time on my side and proper connections i can repower for 1500 for a mpi 4.3 so thats the route im going.. so that ratio swap you were talking about doing that after i do the engine swap correct?? Cause i was planning on that.. or are you saying to swap it for more speed? My boat does rev over so i will try a 17p.. thank you so much for your time

Change the drive at the time you change the engine. Changing drive ratios will not get you more speed, ever. X hp will push Y boat at Z knots. You want more Z, you need more X. The ratio is there to get you into the right prop speed for a given boat. The most common props for these drives are in the 15" to 23" range, so you set the ratio up for each engine given it's likely application, to get the available ponies to gallop so the right prop is in that range... So, theoretically, you don't have to change ratio, you just up the size of the prop until it's right, but there is a practical limit, of what size props are made (there is also an effeciency loss if too big or too small)...

Smaller engines tend to be in smaller boats, proportionally, so get a greater reduction. As the engine power goes up, the boat that engine is to be installed in also goes up, and is usually faster, so less reduction is required.

The opposite also applies. Put an engine that is normally supplied with a 1.47:1 drive into a BIG boat, like a 28 footer, we change the ratio to 1.62:1 or even 1.84:1, just to get the prop back into the 15" to 23" range...

HTH,

Chris........