best motor to repower a 35 duffy???

Mark G

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I am considering buying a 1986 35duffy. It currently has an old volvo in it. the owner says its a 300hp but it looks big to me to be 300hp. If i get the boat it will be with the intentions of repowering it. Looking for some insight on what motor i should be looking for. Thanks in advance.
 

Mark G

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8.3 Cummins pushes them very well. 430-600 depending on what your budget is.
I guess i have to call cummins to get pricing on recon engines. Whats the approx price difference between a 430 and 600?
 

CCtuna

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I worked on one that had a new 6068 Deere in it believe it was 350hp. Cruised 16-18 and topped out a little over 20 and burning almost no fuel at cruise. Boat was rigged pretty heavy too
 

scbob

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If the boat is not too heavy, then maybe a B series Cummins Recon would be a good fit.
Do you intend to use existing transmission ?
Not sure if that would have any influence on your choices.
Bob
 

Mark G

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If the boat is not too heavy, then maybe a B series Cummins Recon would be a good fit.
Do you intend to use existing transmission ?
Not sure if that would have any influence on your choices.
Bob
no would be new transmission also
 

Mark G

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I worked on one that had a new 6068 Deere in it believe it was 350hp. Cruised 16-18 and topped out a little over 20 and burning almost no fuel at cruise. Boat was rigged pretty heavy too
I spoke to cummins this morning, for a new 450-550hp electronic engine with gear youre looking at 55k ballpark. Any idea if deeres are usually cheaper or more expensive than cummins or its all pretty much the same?
 

Powderpro

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I spoke to cummins this morning, for a new 450-550hp electronic engine with gear youre looking at 55k ballpark. Any idea if deeres are usually cheaper or more expensive than cummins or its all pretty much the same?
If going with a new Tier III engine, the QSB6.7 480hp would be excellent, I just powered a new 35 Duffy with that engine. If you wanted to jump up in size, but it will take up more engine room space, the QSC 500 or 600 would be excellent engines too. Cruise speed will be the same on the QSC 500 or 600, more top speed with the 600. The 500 (2,600rpm) and 600 (2,800 rpm) spin the same prop, so all you gain is top speed when comparing the QSC 500 versus 600.

A more economical choice would be a recon QSC500, don’t know how much less a recon is versus a new one, but worth looking at. I would personally go with a recon in a used boat and save the money if they are available.

Deere has a 6.8L in 400hp. Great engine, a little taller than a QSB but a little narrower too. It won’t give you the all out top speed of a 480-600hp Cummins engine, but cruise speed with the 6.8L Deere will be similar or slightly less to what the QSB would be. Deere tends to be a little cheaper, but can’t say that it’s a real significant price difference, everyone has their opinion on what is significant. you would have to price them out and see if giving up a little too speed is worth saving the money.
 

Mark G

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If going with a new Tier III engine, the QSB6.7 480hp would be excellent, I just powered a new 35 Duffy with that engine. If you wanted to jump up in size, but it will take up more engine room space, the QSC 500 or 600 would be excellent engines too. Cruise speed will be the same on the QSC 500 or 600, more top speed with the 600. The 500 (2,600rpm) and 600 (2,800 rpm) spin the same prop, so all you gain is top speed when comparing the QSC 500 versus 600.

A more economical choice would be a recon QSC500, don’t know how much less a recon is versus a new one, but worth looking at. I would personally go with a recon in a used boat and save the money if they are available.

Deere has a 6.8L in 400hp. Great engine, a little taller than a QSB but a little narrower too. It won’t give you the all out top speed of a 480-600hp Cummins engine, but cruise speed with the 6.8L Deere will be similar or slightly less to what the QSB would be. Deere tends to be a little cheaper, but can’t say that it’s a real significant price difference, everyone has their opinion on what is significant. you would have to price them out and see if giving up a little too speed is worth saving the money.
The cummins rep i spoke to said the price on a factory recon was so close to a brand new that he hardly ever sells the recons. I see on ebay guys sell recons for around 30k. I wonder if you can trust them if its not from cummins.
 

Powderpro

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The cummins rep i spoke to said the price on a factory recon was so close to a brand new that he hardly ever sells the recons. I see on ebay guys sell recons for around 30k. I wonder if you can trust them if its not from cummins.
Is it a local Cummins dealer you are talking to?
 

Powderpro

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Mark- it all comes down to how much money you are willing to spend, how much speed you require, and if you need service close by. All these variables will dictate what brand and model you go with. The 400hp 6068 Deere will be the cheapest, but have the slowest top speed and a similar cruise speed to the QSB6.7 480hp. Next up in price would be the QSB6.7 480hp, a little more top speed and a little less weight compared to the 6068 Deere. The biggest engine I would install in a 35 Duffy is the QSC. It obviously will be at the top of the price scale but will deliver the best cruise numbers. Those would be the top 3 engines that I would consider for repowering a 35 Duffy. I'm assuming you already have a 2" prop shaft? If jumping up in HP, I would also highly recommend a 25" or 26"diameter prop, 4 or 5 blade.
 

CaptainDrew

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I am considering buying a 1986 35duffy. It currently has an old volvo in it. the owner says its a 300hp but it looks big to me to be 300hp. If i get the boat it will be with the intentions of repowering it. Looking for some insight on what motor i should be looking for. Thanks in advance.
Hi Mark
I am the Rep for Power Products in New England. I would be happy to discuss a Volvo repower with you. We have several good options for the 35 Duffy depending on what you want to accomplish. I will send you a PM with my contact info.
 

MBILL

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I repowered my 35 Duffy in 2012 with a QSC 8.3L (550hp). It replaced a Cat 3208TA (435hp).
IMO it's a great repower option. My boat is not light and I'm cruising easily at 18 kts.
The QSC8.3 at 550HP is a 3000 rpm engine.

Cummins states that the intermittent use rpm should be 300rpm off the top for no more that 2 hours at a time. I don't have any need to go past 2500 rpm...

The power curve of the engine is great, it makes tons of power throughout the rpm curve, not just at the top like the old 3208 did.
My transmission is a ZF 285A with 1.78/1 ratio. 2" shaft.
 

plowin

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I have a 500hp QSC but it is not in a duffy. It is in a 33’ flowers. The Cummins product has been absolutely flawless so far but I only have a couple thousand hours on it. The company itself sucks in my opinion. The salespeople I dealt with were slow, inaccurate, vague and way more expensive than what it would have been to deal with a certified dealer. Do yourself a favor and find a reputable certified dealer near you and deal with them. Piss on the dealership Itself.

I think its because this week they are working for Cummins, take a class or two and know everything about their engines. Next week they work for Scania, take a couple different classes and know everything about that product and so on. Ask yourself this question. Once your car is out of warranty do you still take it to the dealer to have repairs made or do you go to your long standing mechanic thats seen it all and done most of it twice. This is obviously only my opinion but it comes from past experience with Cummins specifically.

Take Tony Athens owner of Seaboard Marine. He is a huge fan of the Cummins product but has no problem whatsoever telling you or anyone else about any flaws or shortcomings that the product might have.
 
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