240srv Cummins conversion

D

Dackoda

New Member
Sep 20, 2010
12
BC
Boat Info
1974 240 SRV Command Bridge
Engines
351
I have a 240 srv Command Bridge that I use for sports fishing, I'm thinking of installing a Cummins 6BT into this Unit, any suggestions or tips?:huh:
 
well the motor can weigh any were from just over 700lbs to just over 900lbs depends how you set it up, now thats not including tranny and other gizmos, im highly considering repowering the 1977 srv 300 flybridge with twin cummins and running vegi oil through em, one of my employes has a mercedes and runs straight 10 micron filtered burger king oil through his deisel, no bio, no deisel, just straight fast food oil, he has'nt paid for deisel in years other than for his heavy equipment, were checking to see if this will work on the cummins, it should!!!
 
I say go for it and keep us posted! :grin: I'd also be concerned that the drives may need to be upgraded too? I don't know what they can handle compared to what the Cummins puts out?
 
Im Thinking about 300 pounds over the 351w thats in the boat now. I know this boat was available with twins so I dont think the weight should be too much of an issue. I have a volvo sp drive which I think should take the power.
 
It’s possible to do but you will have to deal with gear ratio’s in the outdrives or put the power through a transmission of some sort. Most gas engines (I4, I6, V6, V8) operate in the 4k and above RPM range at WOT and use a (ball park number) 1.5 to 1 up to a 2 to 1 gear ratio. No reason to spin the Cummins that fast when their power is down lower in the tach. Your current drive “may” hold the power but the engine won’t spin as fast and the boat will actually be slower. Heck, the one in my truck stops fueling about 2300 rpm and I cruise at 60mph at 1600 RPM.

I worked on one of the Marine 6BT’s when I was doing some field training and they are cool. I even toyed with the idea of installing a 4BT into the 24ftr I had but, the voices in my head kept telling me to keep it simple and go fishing.

Don’t get me wrong, I’m into doing cool projects but when it comes down to it ya have to ask yourself, how much time and money do I really want to spend on this project to reinvent the wheel and what will I have after it’s completed. I have to tell myself this often to keep myself in check….LOL!!

If it’s something that you really want to do and if you can find an engine and drive package that will push the boat at the speed you want in the recommended engine operating RPM I would say go for it. Just make sure you post pictures for the rest of us to see….:thumbsup:
 
Last edited:
That would be cool!

The sweet spot for the old 6BT rotary pump is about 1,800rpm and was governed at about 2,200 with stock spring. They were about 500lbs over the gas V8. And yes there are plenty of folks running almost anything and everything through them including WVO.

Not sure about the specs and set up for a marine Cummins but don't see why you couldn't copy a modern unit. All it takes is money...

I'd love to have one in ours.
 
If you go Cummins stick with old technology(VP44). New electronic engines will not like the BK oil and Cummins will void any warranty. The old mechainical 5.9 design was the best. Before you start just look into Cummins Marine parts pricing - it can hurt real bad.

Just a thought but what about making your current engine more efficient. I installed a balanced/blueprinted/flowed 496 in a friends go fast - so no actual performace parts installed - and he needed to reprop. It was very smooth and got about 15% better gas mileage running 250-300 rpm's lower for the same speed.:thumbsup:

Like I sad just a thought and way cheaper. But if you want/need to get away from gas the Cummins is not a bad option.
 
If you go diesel, make sure the stringers are strong enough to handle the torque and you don't pull them loose from the hull. The tabbing system on the old SRs was not robust. Some of the tabs were not even glassed to the hull. At least that was my experience with a new 1979 26 EC back in '79.
 
so i called cummins today and spoke with them and was refered to a marine application engineer who works with cummins, whe spoke for over half an hour and summed up the story. you would want to go mechanical pump just like everyones says, older 6bt, as far as all the other goodies you will need a decent size pocket book to complete an automotive cummins over to a marine, now this gentleman offers a repower which are complete and ready to drop in for "are you sitting down" $13,000.00, and thats not including trans, add a new borgwarner and you right around 16k, this gentleman was extremely helpful and was intreaged that we were considering to convert. he does sell all the parts do do the conversion and would help throgh the process, let me know if anyones serious and ill pass his number along
 
Converting to diesel on a smaller boat like that isn't really feasible cost wise, unless you put on an insane amount of hours per season. At $16k, you could purchase qty 8 chevy 350's for that. Even if you purchased one 350 and had 14k left for fuel, a 350 will burn somewhere around 6gph in that size boat. Again, not worth a diesel conversion.

Doug
 
I own a machine shop so the cost of the engine is irrelevent.
 
The Drives our my main consern I have a sp 290 volvo , Im just not sure about the strength of the drive. as far as the gear ratio goes I have thought about installing a planitary drive between the two, Ie modified gear venders or glide, But it might not even be necassary Im happy as long as I can get to about 28 knotts.
 
Doug
The entire disease/addiction/hobby/passion of boating doesn't make good fiscal sense either! I say if you got the know-how and the time and aren't expecting any return on investment other than pure enjoyment (Translation: a boat), go ahead and git-er-done!
 
There was an old Sea Ray on ebay about a year ago with a Cummins 6bt conversion. Trying to remember, maybe a 260 DA. Can not recall the details of cruise speeds and out drives etc.

Whole lot of weight but tons of torque. It may effect getting up out of the water on the smaller boat with all that weight in the back. I know on most of the smaller Sea Rays we would do some shifting of gear to the front to help get on plain while loaded.

Not sure on the outdrives. I would go with heaviest duty you can get, one for the big blocks.

KB
 
rondds said:
Doug
The entire disease/addiction/hobby/passion of boating doesn't make good fiscal sense either! I say if you got the know-how and the time and aren't expecting any return on investment other than pure enjoyment (Translation: a boat), go ahead and git-er-done!
Click to expand...

+1:thumbsup::thumbsup:

Airplanes, boats and hot rods, if you are worried about money and don't enjoy tinkering with them then don't own them. Heres one of my hotrods. I don't have a pilots license or I'd own a plane.

Slam that bad boy Cummins in there and don't look back.
 
Last edited:
I'm all for customizing and hot rodding myself. I've been there, done that.

What I am stating is that there has to be some sort of remote justification from an investment standpoint if you're going to sink $16k in a $500.00 boat. If you're talking $5k or even $10k... I could see that. Not $16k though unless you're going to own this boat for 15 years. I undestand boating doesn't make sense either when trying to justify the hobby from a cost standpoint.

Just sayin'.....

Doug
 
There is a good article in the Oct 2010 Power & Motoryacht that details a 36 year-old Bertram 38 converted to IPS drives for *only* $220,000. The performance gains were outstanding, and in that case the benefits were less weight, better handling, better range and fuel stops that are no longer required. Plus, there's the whole joystick thing.

Only the person writing the checks can determine if it's worth it.
 
Old school, Nice Duster , Seeing you appreciate the Dodges heres a pic of mine
DSCN3147.jpg
 
You must log in or register to reply here.

Forum statistics

Threads
113,246
Messages
1,429,172
Members
61,123
Latest member
Tim Duncan
Back
Top