Gas to Diesel retrofit. Cummins/Bravo III matchup

[Nehalennia]

I want to know if anyone has the newer Cummins-Mercruiser/Bravo III packages. I see that the Cummins-Mercruiser has a QSD4.2 kicking out 350HP and mates up with the Bravo III.
Granted it appears my gear ratio is off and it's probably very cost prohibitive(we'd get a different boat first), but if I were to ever consider a repower on a boat like mine with a Brand new O/D and an '00 5.7K Gas Engine(still with low hours though) is this engine/package worth pursuing?

I realize that it's not a viable cost for the value of the boat, but the package intrigues me and am curious if others have it or have an opinion on it.

 

[H2ONUT]

Todd, I looked into this for the 220. It was a 30K investment. That was with labor. Quoted 2 years ago.

I have been on a SeaSwirl 2101 WA with the smaller Cummins/Mercruiser. Was very impressive. Quicker response than the gas engine, and running at WOT which is 3000 rpm, we were running along at 42 mph. Not sure what the GPH flow is. Much quieter than a gasser also at WOT.

 

[Nehalennia]

Yeah, it sure seems like a very expensive consideration. It may only be a good option if it's ordered on a new/newer boat. It does sound like an interesting package though.

 

[fc3]

Probably a different Bravo drive. Stronger clutch and straight-cut gears instead of helical. I'd imagine a derivative of the old performance Bravo X / XR drives. Even at that, the Bravos aren't really adept a handling big torque. I've seen even hardened straight-cut gears with missing teeth and broken Bravo drive shafts.

Best regards,
Frank

 

[tmhudson2]

Probably a different Bravo drive. Stronger clutch and straight-cut gears instead of helical. I'd imagine a derivative of the old performance Bravo X / XR drives. Even at that, the Bravos aren't really adept a handling big torque. I've seen even hardened straight-cut gears with missing teeth and broken Bravo drive shafts.

Best regards,
Frank

Volvo Penta sells a package mating their Duo-Prop drive to their diesels. Would the DP handle a diesel's torque that much better than a Bravo3?

 

[Nehalennia]

Probably a different Bravo drive. Stronger clutch and straight-cut gears instead of helical. I'd imagine a derivative of the old performance Bravo X / XR drives. Even at that, the Bravos aren't really adept a handling big torque. I've seen even hardened straight-cut gears with missing teeth and broken Bravo drive shafts.

Best regards,
Frank

That could be. All the units I've seen too come with SeaCore. Straight gears v. Helical makes sense too to handle the torque.

 

[H2ONUT]

The Volvo drives for the diesel's are MUCH better than the Mercruiser Bravo.

 

[Tail Chaser 661]

Another 30K option is the Volvo D4 260 hp or 300 hp with the duoprop.
Very good reliable package.
They get a little better then 3 mpg with a heavy 26' boat.
They have about the same TQ as a 454ci mag gas engine.
The 8.1 gas even has lots more power. 11K cheaper then the Diesel package. Gets the same mpg as a 5.7efi at normal cruise speeds.
I have not heard of any drive problems with the Volvo duoprop other then the cost of parts and fewer mechanics for them.

 

[fc3]

Volvo's diesel sterndrive is a different unit than the gasoline ones. Take a look when you go to the boat show. There usually is one on display. Volvo's marine diesels are also higher RPM engines that don't have as much low RPM torque. Not to say that high RPM diesels don't have a huge amount of torque, look at GM's Duramax. But the torque characteristics are different than a Cat or Cummins C series.

Best regards,
Frank

 

[Tail Chaser 661]

The Volvo D4 260 Hp@3500rpm It has 450 lbs of Tq.
Volvo states there high rpm diesels are rated to run at 90% of max rpm. :wow:
The Volvo DPH drive is built for the high Tq diesels.
They use the DPS for there 8.1 gas engines. Cuts thru the water faster? And has very strong gears.
The 8.1 375 hp@4700rpm.
The GM dyno shows like 420tq@1000rpm, 460tq@2000rpm and 509tq@3200rpm
The 8.1 420hp. has like 400Tq at 1000rpm and 440Tq2000rpm.
It also has 509Tq. But its at 3600rpm with max hp at 5000rpm
Seems they should be using the DPH drive on the 8.1's :huh:

Inline 6 cyl diesels are bitchen engines.
I would not trust a Merc sterndrive behind one.
The 6 cyl Yanmar/Merc package would not fit in my boat.
A little to long and high. Check on it two yrs ago.

I am not a fan of any 4 cyl engine.
30K for a sreaming 4 banger diesel package is nuts.
200lbs heavyer then a 8.1 also.
But if you want 3mpg or better and still a reliable product that takes up no room in the bilge. Its an option.

At 18K for a 375hp 8.1
You get 2mpg. Lighter wgt, More power and top end speed then a 4 cyl diesel.

A little bigger boat with a single 6cyl diesel should be by next search.

 

[douglee25]

Another option is the Yanmar ZT350. This engine and drive package will bolt up to a Volvo DP or Mercruiser Bravo III drive transom plate.

Doug

http://www.boattest.com/Resources/view_news.aspx?NewsID=2983

Yanmar Introduces New Stern Drive System - 10/29/2008
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Yanmar’s new lower units are designed for high torque.
The bullet design lower unit is efficient and effective.
Yanmar says it has serious corrosion protection built in.
The lower unit employs counter-rotating dual props.
Yanmar is jumping into the diesel stern drive market in a big way with the global introduction of its new ZT350 stern drive. Yanmar has actually been building stern drives for the Japanese market for over 20 years, so is no stranger to the stresses put on these drive trains in the saltwater environment. Yanmar’s ZT350 has a multi-friction plate clutch, not a cone clutch which is used in some competitive units, and thereby provides smooth, quiet shifting without the “clunk.” The unit is designed so that its mounting transom plate and bolt holes line-up exactly with those of both the Bravo III and Volvo Penta’s DP lower unit. Now Yanmar makes and is responsible for the complete drive train system from ignition to prop.
​

 

[Chip1976]

Hello I have a 1994 290. with two Merc V6. both engines are damaged and I like to repower to diesel. What are my best options? With leaving the transom etc as they are.
Any ideas anyone?
Thanks

 

[joe and ali]

I found this site/article that you all might want to check out. It makes sense to me.
joe
http://www.yachtsurvey.com/GasNdiesel.htm

 

[Tail Chaser 661]

I found this site/article that you all might want to check out. It makes sense to me.
joe
http://www.yachtsurvey.com/GasNdiesel.htm

That was part of my decision going with the 8.1 Mag.
Same TQ as a 320 HP inline Six Diesel. Which is also a stern drive killer.
A complete 8.1 package is 14K cheaper then the 6 cyl diesel, and 10k cheaper then the 4 cyl diesel.

There's too many water ingestion marine engine failures
to risk the High Dollar diesel package.(When its not needed)

When boats weigh over 14000 lbs. Then the inboard diesels start to become a good efficient needed package.

I will be giving up 1 mpg going gas instead of diesel. :smt089