1974 Volvo to Mercruiser Conversion Questions

[Mknick]

Hey all,

I have a 1974 Glastron V-254 Caribbean with original dual Ford 302's I/O's that I recently acquired. It is a fairly rare boat. Seeing as the Volvo 270 outdrives on it lack any trim and as upgrading it to Volvo 290's, 290dp's, or any other volvo product is going to be 2-3x as expensive as mercruiser, I have a strong desire to convert the current setup to Mercruiser outdrives. As well as that, it seems like Volvo 270 parts are relatively difficult to find. I am located in the US near the great lakes.

I know that my 302's (that may be upgraded to 351w's in the future) are essentially the same as certain mercruiser I/O engines from that time such as the 888. However, Mercruiser hasn't used Ford's for a long time since then.

The motors were bought by Glastron in the 70's and taken to their factory where they "Marinized" them before putting them into their new boats.

My goal is to keep the engines on it as is for now, and swap/upgrade out the volvo 270 drives with a Merc product. I would like to go with the latest model Bravo drives I can, but I'm not sure about reliability vs Alpha drives. Not a deal breaker.

I also realize that shifting will be different. The current setup is hydraulic actuated shifting, so hopefully this isn't too much of a pain. Also has hydraulic steering.

Additionally, I know that there are adapter plates out there for this purpose for $600-$1500 each.

1. How much would I need to swap out if I had the transom adapter plates? What about Alpha vs. Bravo Drives? I'm assuming I would need to pull the engines from what I know, and this may be in the near future for performance reasons. Or would it be possible to reuse the Volvo inner transom adapter plates in place? Would I need to worry about adjusting the motor/motor mounts to account for the new mercruiser drive?

2. How reliable are Bravo II/III drives? Any maintenance cost differences besides the props being a little more expensive?

3. What drive would you recommend for around 300hp per engine in the future?

4. For the $1400 it's going to cost in a set of transom brackets, would it be more worthwhile to just get the transom rebuilt with something that doesn't rot? Not sure about me doing a transom rebuild vs having a small dry dock or someone similar do it. My dad does have fiberglass auto body repair experience, so it shouldn't be too hard for him to translate those skills into transom replacement help if it comes to that.

5. Additionally, while the current transom is super solid, I have some worry about it being too thin. I've read some threads in other places that talk about potentially needing to add thickness to the transom when converting from Volvo to Merc, but I'm not sure if that applies in my case. The last measurement I read was 2" - 2 1/8" required thickness. I don't know what my thickness currently is.

 

[achris]

Hello and :welcome: aboard.

1. How much would I need to swap out if I had the transom adapter plates? What about Alpha vs. Bravo Drives? I'm assuming I would need to pull the engines from what I know, and this may be in the near future for performance reasons. Or would it be possible to reuse the Volvo inner transom adapter plates in place? Would I need to worry about adjusting the motor/motor mounts to account for the new mercruiser drive?

Using the adapter plates, you do a complete swap, all the Volvo stuff comes out, all Mercruiser stuff goes in.

2. How reliable are Bravo II/III drives? Any maintenance cost differences besides the props being a little more expensive?

The Bravo drives are very reliable, and good to about 600hp.

3. What drive would you recommend for around 300hp per engine in the future?

Alphas are good to around 300hp. And a lot easier to get, more people know how to work on them, and quite a bit cheaper than Bravos.

4. For the $1400 it's going to cost in a set of transom brackets, would it be more worthwhile to just get the transom rebuilt with something that doesn't rot? Not sure about me doing a transom rebuild vs having a small dry dock or someone similar do it. My dad does have fiberglass auto body repair experience, so it shouldn't be too hard for him to translate those skills into transom replacement help if it comes to that.

That's a question only you can answer. You'd need to get rebuild estimates and weigh it up.

5. Additionally, while the current transom is super solid, I have some worry about it being too thin. I've read some threads in other places that talk about potentially needing to add thickness to the transom when converting from Volvo to Merc, but I'm not sure if that applies in my case. The last measurement I read was 2" - 2 1/8" required thickness. I don't know what my thickness currently is.

The full spec is 2" to 2-1/8", with flatness and parallelism to 1/16".

...The motors were bought by Glastron in the 70's and taken to their factory where they "Marinized" them before putting them into their new boats.....

No. The engines were bought by Volvo (or Mercruiser), marinised and have the stern drive added to the package. Glastron (and all boat builders) then buy them as a complete package from Volvo (or Mercruiser) and just install them in a boat... No boat builders marinise engines.

Chris......

 

[Mknick]

No. The engines were bought by Volvo (or Mercruiser), marinised and have the stern drive added to the package. Glastron (and all boat builders) then buy them as a complete package from Volvo (or Mercruiser) and just install them in a boat... No boat builders marinise engines.

Chris......

Thanks for all the info Chris. For the Marinised part I was talking about, I learned about it here, it talks a little about it on this page: http://www.classicglastron.com/gl-reflt-p18.htm

 

[Mknick]

Hello and :welcome: aboard.
Using the adapter plates, you do a complete swap, all the Volvo stuff comes out, all Mercruiser stuff goes in.
Chris......

With this in mind, I assume my 302's will connect up just fine to an alpha or Bravo once I swap out the transom assemblies and lower units? I'm not sure about driveshaft lengths or anything in that area that with a volvo leg vs mercruiser alpha/bravo leg.
I know the mercruiser 888 existed, but I'm not sure if the engine mounts/driveshaft length would differ between a Volvo 270 with a Ford 302(Glastron 165) VS. a Ford 302 (Mercruiser 888) with an Alpha/Bravo leg.

 

[Scott Danforth]

its going to be cheaper to sell your boat and buy the one you want.

to switch to a mercruiser, you need a different transom. the transom adapter plate that may have existed in the past is NLA, and the last one I came across had a price tag on it of $2000each and that was in 2011

Mercruiser hasnt used Ford engines since the early 70's so a newer (better) drive wont work with the ford motor as the transom shields changed and there are no ford flywheel housings for the newer transom shields. so an Alpha 1 G2 and a bravo is out with a ford motor. you could find a mid 90's volvo penta SX drive setup, however many of those ford specific parts are NLA

now, if you swap out a complete bob-tail from pulley to props and re-build your transom you can do anything you want.

BTW, if you shop around, you could upgrade to a pair of 290dp's for about $3-4k that is transom shield to props. but your still talking 30-35 year old drives

but you can also find a pair of 4.3 bob-tails with alpha drives on them with 220hp each for about $2500 each which will run circles around the old ford V8's

 

[Mknick]

its going to be cheaper to sell your boat and buy the one you want.

to switch to a mercruiser, you need a different transom. the transom adapter plate that may have existed in the past is NLA, and the last one I came across had a price tag on it of $2000each and that was in 2011

I did find the transom adapter plates for $700 each recently, so not out of the question yet. Mercruisers just seem more common and easy to work on and find parts for vs Volvos, but I may be wrong on that.

Mercruiser hasnt used Ford engines since the early 70's so a newer (better) drive wont work with the ford motor as the transom shields changed and there are no ford flywheel housings for the newer transom shields. so an Alpha 1 G2 and a bravo is out with a ford motor. you could find a mid 90's volvo penta SX drive setup, however many of those ford specific parts are NLA

So an easy-ish complete drive swap from transom plates back to a Mercruiser drive is out of the question. Got it, thanks.

now, if you swap out a complete bob-tail from pulley to props and re-build your transom you can do anything you want.

Tempting, but pricey. Misewell stick with semi similar vintage as much as possible.

BTW, if you shop around, you could upgrade to a pair of 290dp's for about $3-4k that is transom shield to props. but your still talking 30-35 year old drives

but you can also find a pair of 4.3 bob-tails with alpha drives on them with 220hp each for about $2500 each which will run circles around the old ford V8's

On the Volvo upgrade option, I did start another thread on the Volvo side of the forums right before I saw your reply haha: https://forums.iboats.com/forum/engi...0dp-lower-swap

The DP swap is definitely something I've considered. I figure if I end up swapping the existing motors to 351w's later on and doing some mild performance upgrades to 300hp or so each, I should have a nice zippy 55mph boat, and the dp's should do great with 300hp. But the the other thread is probably the best place to talk about it.

The old Ford 302's seem like they're easy enough to find in junkyards if/when something happens to one or both of the current motors, so sticking with them seems logical at this point.

The boat is fairly rare, and I paid $1100 for it. Not desirable, just rare. I saw one of my same V-254's a few months ago in great condition advertised for $17,000. So not a bad price for what I got.

 

[Scott Danforth]

define rare........ millions of boats are low-volume. in fact hundreds of thousands of boat builders have come and gone making less than a dozen boats..... doesnt make them valuable.

remember, to get your $1100 boat to a $1700 boat may take $5-10k and 5 years worth of work.

 

[Mknick]

define rare........ millions of boats are low-volume. in fact hundreds of thousands of boat builders have come and gone making less than a dozen boats..... doesnt make them valuable.

remember, to get your $1100 boat to a $1700 boat may take $5-10k and 5 years worth of work.

Yep, that's true. I need a hobby though, and this is a good one for now. Can't be all fun and no work, right?

 

[achris]

Thanks for all the info Chris. For the Marinised part I was talking about, I learned about it here, it talks a little about it on this page: http://www.classicglastron.com/gl-reflt-p18.htm

Not sure why they said 'converted', because, as I said, boat builders bought engine packages complete from Volvo and MerCruiser. No boat builder has ever needed to do any conversions....

Anyho, as Scott said, once you have the transom sorted out, the MerCruiser gimbal housing mounted up, then you have to set the back of the engine up with the MerCruiser flywheel housing and coupler. And unless you go for (now very very old) MC1s, MerCruiser never made a new style flywheel housing for the Ford engines. You're also going to need to change to Merc exhausts too.

There MIGHT be a way through. You'd have to do a lot of research and double checking... But here goes.

The old style flywheel housing will sit on the later MC1 inner transom plate. A while ago I checked and seem to remember the bolt pattern is the same for the later MC1 and the Gen II... So, using the 75-81 inner and Gen II gimbal housing MIGHT offer you the option to use an Alpha One Gen II drive... But as I said at the beginning, I've not done it, and it's only theoretical...

The better option is changing to a couple of 4.3s... great engines, that will eat the Fords for breakfast... The 4.3 will make 225hp at the prop. Even the 351 in marine guise was only 233hp, at the crank! (Barely 200hp at the prop)...

Chris.

 

[Scott Danforth]

if your married or dating, you better get approval from your other half

if your single, dont plan on a social life.

the resto-mod in my signature is still not completed, however coming up on 5 years. I estimate I have about 5500 hours of time in it not to mention about $8-10k if I added all the receipts. my guess I have $500 in stainless screws from the local hardware store alone.

would I do it again, probably not. my next boat will be a 2010 or so that someone neglected the engines in salt water and didnt change the manifolds and it hydro-locked and I will simply do a weekend re-power. in the long run, it will be much cheaper.

 

[Mknick]

Not sure why they said 'converted', because, as I said, boat builders bought engine packages complete from Volvo and MerCruiser. No boat builder has ever needed to do any conversions....

I don't know either, that's one of the only places I've ever read about something like that. Glastron was big, and they have their badges on both the engines and outdrives, so who knows? But doesn't really matter one way or another. Have to find the plant manager in the pic I guess and ask him.

There MIGHT be a way through. You'd have to do a lot of research and double checking... But here goes.

The old style flywheel housing will sit on the later MC1 inner transom plate. A while ago I checked and seem to remember the bolt pattern is the same for the later MC1 and the Gen II... So, using the 75-81 inner and Gen II gimbal housing MIGHT offer you the option to use an Alpha One Gen II drive... But as I said at the beginning, I've not done it, and it's only theoretical...

The better option is changing to a couple of 4.3s... great engines, that will eat the Fords for breakfast... The 4.3 will make 225hp at the prop. Even the 351 in marine guise was only 233hp, at the crank! (Barely 200hp at the prop)...

Chris.

If I was going to go with a new set of powerplants for it, Merc or Volvo, I would want them to be 300hp, or approaching 300hp each. I might even be able to do it by tweaking the current 302's, or the potential future 351w's but that's a path I haven't decided whether I should go down or not just yet. Since the boat was $1100, I wouldn't have much to lose by doing it.

I kind've want to go a route where I get some experience taking some of it apart and doing work on it rather than going the easy route of just dropping in a new power plant right now.

All that being said, I will earmark this as a potential future full upgrade if/when the time is right and the research adds up. Merc or from the other thread link above in the Volvo forums, GM, may be the way to go. This will probably be a couple years down the line once I've gotten bored with it.

 

[achris]

For 300hp, you're going to need to go to vortec 5.7 GMs... To do it with 351 W, you'd probably need too much cam, and introduce exhaust reversion...

Chris.

 

[Mknick]

For 300hp, you're going to need to go to vortec 5.7 GMs... To do it with 351 W, you'd probably need too much cam, and introduce exhaust reversion...

Chris.

There seem to be a lot of 302's out there that have been beefed up, I don't know about low end torque changes from changing the cam up. I know that I will most definitely need more exhaust as the current 270's restrict it too much. Need to find one done on a boat and go from there.

 

[achris]

There seem to be a lot of 302's out there that have been beefed up, I don't know about low end torque changes from changing the cam up. ...

And there's the nub of the 'problem'. Unlike cars, boats have a single reduction gearbox, and fixed pitch prop. What you throw it in the water with, is what you are stuck with.

We hear all the time that a 5.7 litre engine is quite capable of making more like 500hp, and at 260 or 300 is 'underdone'. But with a boat, you NEED that low end and mid-range torque and power that is the trade off for high end power. There's very little point in making an engine that's going to push to boat up to 60 or 70 knots, if the bottom end is so lacking that it can't even produce enough power to get on the plane in the first place. And also remember, it gets worse as you make more power. As the top end power increases (at the expense of low end), the pitch of the prop needs to be increased to keep the revs in check (and in the right range to utilize that extra power). And as you decrease low end, and increase pitch, the problem of just getting up on the plane gets harder.

Personally, I'd be happy to leave 100hp 'on the table' to achieve a boat with excellent 'drive-ability'.... I run a 17" prop, and at WOT on a good day, I'm just banging on the rev limiter, and running 40 knots. With a 19" prop, the WOT is 4600rpm (bang in the middle of the recommended) and 43 knots. But the 17" is my choice. Why? Because on the days when I'm running home with a 3 metre swell and a 25 knot breeze on top of that, the 19" drops the revs down below the power band, and the engine struggles up one side of the swell, then revs it's box off down the other side. I'm constantly having to work the throttle to keep from either bogging down and having a swell dump a ton of water over the stern, or going so fast that the boat's bouncing around like a cork. With the 17" I can set the boat up with the bow trimmed up a bit, the throttle set to give me about 17 or 18 knots, and it only varies by a couple of knots. The engine's happy, the boat's riding through the water with ease, my passengers are happy and comfortable, and I'm a happy camper.

And the number of days a year we get weather good enough to properly use that extra speed can be counted on the fingers of one hand.

Power isn't all it's cracked up to be. As I said, I'm quite happy to sacrifice (potential) top end power for a nice strong FLAT torque curve.

Chris.......

 

[nola mike]

I'd be looking for a couple of trash hulls with 5.7s/5.0s in them. I'm in the middle of a much simpler swap, and it's still taking way too many creative solutions. Between sourcing parts and figuring out what you need to do (you'll be in uncharted territory for many problems) you'll never get on the water

 

[Scott Danforth]

the only way you will get 302's to 300hp with a marine cam limited by wet exhaust is with a blower

many marine 302's were built with GT40 heads and the 351 cam (check firing order)

you can get the 351 to 300hp, you can get a 350 to 300hp

for the same cost, you can build a 383 SBC and make 350hp all day long running wet exhaust.

or, as I stated, you can buy two 4.3 long tails for about $2500 each and drop them in there to have more power at the props than the 351's did back then. or for about the same price buy 2 5.7 long tails and swap to 4 barrel carbs

much cheaper than rebuilding the old ford stuff you have

 

[muc]

Not sure why they said 'converted', because, as I said, boat builders bought engine packages complete from Volvo and MerCruiser. No boat builder has ever needed to do any conversions....

Chris.

That is not correct.

Back in the 60s and 70s a few boat builders did their own Marinisation. Iv'e been told that at one time Chris Craft was producing more engine packages than MerCruiser. Most of the I/O’s used Volvo drives, but I have seen Eaton, Dana and a few others. The Chrysler slant 6 and 318 ci were very common. Chris Craft liked the 307ci and 327ci, sometimes they would install the engine backwards. Flywheel to the bow of the boat and Use the damper end of the crankshaft for power output.

Finding exhaust manifolds for some of these oddball packages can be tough to find, but I’m guessing that they should be available for the Ford because Glastron used a lot of them. There are a few other parts that you will have to adapt or have custom made.

To the O.P.
If you want to have much value. And yes I do see stuff like this sell for $17,000 and up. You need to keep it completely stock. This means engines, drives, vinyl, fiberglass and electrical. Anything that you do that changes the boat decreases the value. But at that point you will have a boat to work on and look at. And if you actually want to go boating, you will need a different boat.

 

[kenny nunez]

2Xs on Muc. I once owned a 21’ Donzi with a 300 hp Chris Craft Chevy. It had a really weird cooling system and a bronze circulating pump mounted different from the stock water pump. It had a 30-30 solid lifter Duntov cam And a Weiand aluminum manifold. I found all this from someone at Chris Craft.
I once met Lee Holman of Holman& Moody who told me that when they were marinizing the Ford engines with Volvos they could not produce them fast though to meet the demand.

 

[achris]

That is not correct.

Back in the 60s and 70s a few boat builders did their own Marinisation. Iv'e been told that at one time Chris Craft was producing more engine packages than MerCruiser. Most of the I/O’s used Volvo drives, but I have seen Eaton, Dana and a few others. The Chrysler slant 6 and 318 ci were very common. Chris Craft liked the 307ci and 327ci, sometimes they would install the engine backwards. Flywheel to the bow of the boat and Use the damper end of the crankshaft for power output....

I stand corrected. Thanks for the info...

Chris...

 

[Mknick]

To the O.P.
If you want to have much value. And yes I do see stuff like this sell for $17,000 and up. You need to keep it completely stock. This means engines, drives, vinyl, fiberglass and electrical. Anything that you do that changes the boat decreases the value. But at that point you will have a boat to work on and look at. And if you actually want to go boating, you will need a different boat.

As a sidenote, the twin to my current V-254 down in Florida was an outboard conversion. Someone also removed the upper helm controls on that one. I can't find it anymore on Craigslist, so it was taken down or sold for that 17,000.

I read here https://www.hagerty.com/valuationtools/classic-boat-values/collector-boat-classification that a repower is acceptable, but the bounds of acceptable change from time to time. Seeing as it already had a set of EPA restricted V8's, putting a set of Mercruiser 5.7's in it seems to be the next logical step for my future repower. I might even get lucky and find a salvage boat with the motors I need, who knows? In either case, 250-300 each hp sounds just fine. Have to balance speed with gas mileage after all.

With keeping it original, I will probably do some hidden quality of life upgrades to the electronic system, but then again, maybe not. I have no idea how much changing little things will have on the value of the boat in the end. For example, when I re-do the cuddy cabin, I'll probably put in memory foam or similar, unless the original proves to be comfortable. I'd like to also add on a small generator somewhere, as well as a decently sized battery bank. Enough to run a mini fridge and microwave at least. Maybe AC if I get that bored, but keeping it in theme with the rest of the boat.

My main upgrade goal is to add utility and such while keeping it looking original on the surface. But, also not going too overboard.

If you have any additional insight or advice on keeping it original other than that I'd love to hear it.