Diesel engine upgrade

Bibapulula

Cadet
Joined
May 12, 2018
Messages
23
What diesel engines will be easy to fit in my bayliner 2855? Today it runs with a mercruiser 7.4/B3 outdrive.
Is there any diesel engines that fits the engine mounts?
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Howdy,

Welcome aboard!

There are a few Mercruiser diesel engines that will work. There may be others. You're in the NON-repair OUTBOARD forum though.

This post might be better served in the NON-repair I/O section or the Diesel engine forum

There is a forum that this question might be better in. A MOD should be along to move it.

Cheers,


Rick

Let me also add that the cost involved will be more than the boat is worth even if you get it to work.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,295
other than a converted duramax diesel, none will fit your flywheel housing and mounts.

there are very few duramax diesel conversions out there. Banks is one of them.

it would be easier to buy a complete pulley to prop diesel setup and modify your hull as needed.

what problem are you trying to fix?
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Is there any diesel engines that fits the engine mounts?

Finding a motor that will fit the original engine mounts is pennies compared to the conversion cost. A small amount will move the mounts where ever they need to be. The issues is weight and torque. The 7.4 is heavy enough, but to get a diesel that has as much torque as the 7.4 will weight more and have less hp.

You'll get better fuel economy but less speed. Compare any cruiser with gas over diesels and the speed is less. Figuring you want economy over speed, and the standard B3 drive will not hold up with a diesel

Be better if you really like the boat and want to spend the coin, suggest going for twin small blocks, or put a 502 MPI in it. Mine was barely doing OK with a 502 MPI but I'm 3K pounds heavier the yours
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Right. The standard Bravo III would have to be replaced or rebuilt.

Mercruiser does have the Bravo IIIx drive for diesels I believe.

Agree, the upper is what needs to be changed, the lower is the standard B3 and doesn't change between standard, X, XR
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,295
Right. The standard Bravo III would have to be replaced or rebuilt.

Mercruiser does have the Bravo IIIx drive for diesels I believe.

the little CMD 2.8 (VM sourced) diesel came with Bravo 3s

the new Audi sourced 3.0 is also paired with B3s.

the 4.2 Audi sourced 4.2 is not and the Cummins 6.7 could be had with the NXT drive (now discontinued), however its usually inboard only.

there are a few duramax conversion companies out there, however most went under. the only one left standing is Banks

https://official.bankspower.com/project/custom-projects/banks-super-turbo-marine-diesel/

lowest cost route would be to drop in a 502MPI or rebuild the motor that is in there and change some major components.

however need to know what the main issue is

lack of power?

it cant be economy, as boats do not get economy.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
board only.

there are a few duramax conversion companies out there, however most went under. the only one left standing is Banks
There was also Peninsular Diesel who marinized the 6.5L GM diesel and changed the injection pump to mechanical.

It was successful but the the cost was prohibitive. Again, you can replace your 454 with a rebuilt and upgraded 454 or 502 and still have a LOT of money left over to buy a LOT of gasoline.

AND still have far better performance than pretty much any of the diesels available.

Mercruiser does have the VW TDI V-6 diesel conversion and they're nice running. (370hp I think + fuel consumption is a fair amount less) But for the cost, unless you're in some sort of business where you can depreciate and make money with the boat, it'll never payoff.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,295
Peninsular and about 4 others that went out of business.

there was a post not to long ago for someone looking for replacement peninsular or similar exhaust manifolds.... even more rare than NOS OMC 5.8 EFI parts.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Peninsular and about 4 others that went out of business.

there was a post not to long ago for someone looking for replacement peninsular or similar exhaust manifolds.... even more rare than NOS OMC 5.8 EFI parts.

There was also a guy here that put a 6.2 NA diesel in his Bayliner (I think) and when it was all done, it would barely get out of it's own smoke!!

I think he had to make his own SS jacketed exhaust manifolds
 

cptbill

Senior Chief Petty Officer
Joined
Oct 6, 2012
Messages
732
Forgive me for asking this because if you want to convert to diesel have at it but I owned a 1999 2855 7.4 bravo III that I bought new and the thing would scoot across the water at very close to 50mph and just running on plane it was as fuel efficient, It would even pull a skier. If it needs repowered I'm not seeing any advantages
 

Bibapulula

Cadet
Joined
May 12, 2018
Messages
23
The reason I asked the question is that gasoline costs twice as much here in Sweden as in the USA. About 7dollar/gallon.
I like the boat but fuel costs with the 7.4 are very high compared to my friends diesel boats in the same size.
Mercruiser has an 6cyl 4.2 diesel with 300-320hp, any opinions on that engine? Will it fit in the engine bay?
A used engine with low hours is somwhere between 5-10k.
The easy way out of this is to sell the boat an by another diesel powerd one. :D
 

cptbill

Senior Chief Petty Officer
Joined
Oct 6, 2012
Messages
732
Ok I get it now, Just my opinion now but it seems to me that by the time you add up all the costs(especially all the little things needed to make the conversion) you just might be better off buying a diesel boat
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Mercruiser has an 6cyl 4.2 diesel with 300-320hp, any opinions on that engine? Will it fit in the engine bay?
A used engine with low hours is somwhere between 5-10k.

When you said 4.2L engine I thought you might be talking about this one:
https://www.mercurymarine.com/en/us/engines/diesel/mercury-diesel/42l-tier-3/

New, this engine is going to cost a small fortune....but it would probably be the right engine to get decent performance in a boat the size of a 2855.

Mercury calls it a "TDI" which makes me think it might be one of the TDI family of engines from VW. Outstanding engines to be sure! I would LOVE to have that engine in my 21ft Four Winns but to run it you would likely need to change to the newer Bravo IIIx drive.

I know they do use the V-6 TDI engines too. If you could get one cheap enough and do the installation yourself, it might be a good choice since your gasoline powered boat won't be worth a lot as is....

If you had to pay someone to do the entire swap, it may well cost more than the boat would be worth once you were done.

You should investigate the cost of finding a similar size diesel powered boat and compare.

I think the VW V-6 TDI is this one:

https://www.mercurymarine.com/en/us/engines/diesel/mercury-diesel/30l-150-270hp/

However, the V-6 might be a little underpowered for your 2855

Regards,


Rick
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,295
the 4.2 audi sourced diesel V8 is ok, however you will need a complete bobtail. not just the engine. a complete bobtail

then add the cost to convert the remainder of the boat over. (transom shield, y-pipe, fuel system).

petrol fill systems are 1.5", diesel fill systems are 2". you will need to change the fuel tank over for the diesel fuel return (needs to return to opposite end of tank than the supply)

you are always cheaper off selling what you have and buying what you need unless you like spending time and money on projects.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
I’m pretty sure there is a 6.5 gm turbo charged diesel that would fit straight in. It’s used in the hummer
but it will be a compromise and will certainly require serious thinking about drive ratios etc. They are really heavy too.
There is a guy here in the U.K. that marinises the superb BMW 6 cylinder 3.0 and merc 3.0 engines. They are ideal and he mates to your bell housing. They have almost identical rpm power bands to the GM V8
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,295
The companies that were marinizing rhe duramax went out of business years ago with the exception of Gale Banks.

We covered it already
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
There is a yanmar and yamaha (Toyota based engine) that will fit. Think it’s called an sti or something.
Whether it’s an upgrade or not...I’m not so sure. Especially if you are in the US with cheap petrol prices. Generally the cost of doing such a thing correctly (changing drives or ratios to suit) means that you would be cheaper buying another boat.
Not to mention the noise and loss of refinement...unless Diesels have come a long way...but doing the sums on it you’d need to be certain you are doing some crazy long distance journeys and keeping the boat for decades to see any real return financially.
 
Top