Cummins QSB 6.7's

[jayjays1]

Hello folks. Does anyone know of anyone successfully re-powering a B31 with Cummins QSB6.7's?

Let me know if you know of anyone.

JJ

[Ironworker]

JJ,

I looked at the 6.7's hard when I repowered. For a variety or reasons I went with the 5.9's. Read the owner's manual first. The 6.7s are not supposed to be idled for long periods of time i.e., trolling speeds. There is also more unnecessary stuff to break. They are also bigger.

Of course there are many that will make the argument for mechanical engines but I wanted the electronic for quietness and lack of smoke. While I don't have a lot of hours on the 5.9's, I'm happy so far.

[jayjays1]

Thanks Rick. I have come into a FB 31 but it is actually one for which the bridge is only screwed/bolted on. I commute to work by boat each day but I have to get under a small bridge to do that. My 31 with a FB just gets under at high tide but one false move and I will be down a precious FB windshield so don't want to chance it. The sedan version will be ideal for this run and, not wanting to be late for work, I need as high a cruise speed/hp as possible. This is why I am thinking of the 6.7's but I just want to make sure that they can be made to fit. The excess weight will be compensated as I will have no heavy FB, no sink, AC or genset. This will strictly be a commuter boat.

Any knowledge on putting these motors in would be appreciated from anyone of you.

Sincerely,

JJ

[Tony Meola]

JJ

What engines are in her now? That will help determine what you are going to need to do. If you have gas in her you could be in for a lot of work.

[jayjays1]

Hey Guys she is a wreck right now with old gasser Mercruisers but not sure which model. I am just trying to discern if the 6.7's will actually fit albeit with complex mods.

Will they? Anyone tried before?

JJ

[Amberjack]

JJ, where will the helm be?

[jayjays1]

Will have a downstairs stbd helm.

[Amberjack]

I’ve seen pictures of 31 sedans at speed but don’t see how they do it. I think the sight line on a 31 needs to be at least a foot or so above the coachhouse roof for adequate visibility at any speed above idle. About where Carl sits. Any lower the bow obstructs the view forward when on a step.

[jayjays1]

Interesting point. In my B25 sedan the view is restricted while getting up on the plane but is fine once on the plane. Mind you it has the benefit of the i/o cavitation plate! Definitely enough sedans out there so there must be adequate visibility at least. She will also have trim tabs to help keep here level in side chop so I expect that they will help also.

[Yannis]

There are several discussions on this site that point out what Doug says, in other words, that visibility is severely obstructed by the bow.
The fact that many sedans exist doesn't adequately explain about visibility, as it is the speed of the boat that determines the bow attitude. Perhaps, with old gassers and low speeds, the bow stays down, however with 370 diesels the bow may be so high that you risk more than you want.
Additionally, if you consider what Bob explains about his own boat, whereby he considers a lifted bow to be the optimal angle for cruising (I think he has 370’s not sure which type), then visibility is certainly an issue from a lower station.
And Carl sits outside on pedestal seats with his eyes well above the coach roof.

[jayjays1]

Thanks Yannis will consider this. I currently have an FB with 370's in her so what I will do is see how bad the effect is from downstairs while my friend drives from up top.

[Ironworker]

Hey Guys she is a wreck right now with old gasser Mercruisers but not sure which model. I am just trying to discern if the 6.7's will actually fit albeit with complex mods.

Will they? Anyone tried before?

JJ

JJ,

You will need to rebuild the engine beds. Thats not a big deal but it is going to more work. If you go to the Cummins website or a couple of other places online you can find a dimensional drawing of the engines. I built a wooden engine model that I used to rebuild my stringers. My stringers are built from glass/epoxy laminated coosa.