Marinette Boat Forum

I have a Cummins 4BT I picked up in a trade for a couple of truck axles, I have next to nothing in it, and it needs a home, one of my old trucks or my boat. I could possibly trade it for a 6BT to a friend for a little money. It came out of a bread truck and it has the Chevy engine bell, find a GM bell, coupler for the velvet drive and I'm set, (the GM engine bell will fit the 6BT if I decide to trade).

Building the components (exhaust manifold etc.) to make it work for marine service is not an issue, I enjoy building things.

The diesels are expensive and they are a pain in the a$$ to install subject has been beaten to death, performance and components needed has not.

Most of my cruising with my current single 318 is around 10 MPH at 2,000 RPM, the 4BT would be lower RPM at 10 MPH than the 318 , but I believe it would suffer on the top end. I don't want to run on the governor all day and burn it up.

Anyone have a 4 or 6BT and have any fuel mileage, RPM, speed numbers? (I've heard twice the mileage and twice the speed, with a 6BT)

Would a 1:1 tranny work or would you need a 1.5:1?

Would the 71 Borg Warner be heavy enough or would you need a heavier tranny?

What size shaft would you need?

What size, pitch prop would you use with either tranny?

This is not a for sure thing for me, more of the pros and cons, something to think about. Let's take a look at the advantages, disadvantages of diesel and gas, excluding the money and work needed to do the swap.

Just thought of my diesel question again, and thought I would bring it back to life with no answers yet. You may not have any experience with owning a diesel yourself, as I do not either. Any thoughts at all? It would be nice to have long range cruising ability, I believe the 4BT would be perfect if you cruised at 10MPH all the time (sippin' fuel), it would suck to be far away from port on a Sunday and have to be back at work on Monday though. The things that make you go Hmmmm????

The modern thin wall Compacted Graphite Iron CGI diesels (cementite iron) are completely different in metallurgy from gray iron old diesels. That's the likeliest choice for a killer diesel to fit the planing hull of the Marinette. http://blogs.dieselpowermag.com/6597844 ... urability/ There are a few diesel electrics for recreational boats by Siemens.

I've never seen one, but I have herd of what is called a pancake engine. It is essentially a 6-71 Detroit sitting sideways, for use in busses where low clearance is an issue. Would make an awesome engine in a Marinette. My brother and I used to build 2 stroke Detroits at a diesel shop we used to work at. One of the coolest things I ever done was to run a 12V-71 in a box, on the floor with open exhaust, to set the racks (RPM) and check for leaks. They are noisy and they will eventually leak, but I still love the 2 stroke Detroits, very cool engines.

First I would like to say dont get upset. You are asking for opinons. I have owned a Auto repair shop for over 20 years. Built transmissions, and engines , owned and repaired boats inboard and outboard. for 20 years. I assume you have a single 318 with a 1to1 velvet drive , 1 inch shaft. Approx 12" prop If so. To put a bigger diameter prop you would have to change the packing tube. And have a taller strut made. And possably change the angle of the engine to get the prop clearance from the hull. To use a 1.5 trans I dont think you will be able to get a big enought prop ,to be able to run the engine at the rpm you want to run. If 2500 rpm is your max. Then you would need a 1to1 trans and a huge prop. Which will not fit under the hull now. If 2500 is your number. A 1to1 velvet drive 72 not a 71. To be safe a 1" 1/2 shaft and room for a 20" prop is where i would think about starting. Then you have the height of the engine to consider. It will be tall because of the angle. The plus is you are running a single. Them the noise to consider. A diesel in a aluminum boat will be loud. It will be alot of work. Personally If you need to entend your range, just add a tank ,or put a bigger one in. Fill it up! get some beer and enjoy your self. Them old chryslers are hard to beat!!!! Just have to feed them. Joe

Thank you for your thoughts, valid points. One question though, wouldn't a smaller steeper pitched prop do the same thing as a larger lower pitched prop, eliminating all the angle issues, as long as you don't go so far as to cause cavitation? Just a guess, but say a, 16X16cupped vs. a 20X11?

The more I think about it, I think my best bet is to put the 4BT in my old Ford, enjoy 25- 30mpg, and put the fuel savings from there into my boat tank. In contradiction to my original question, it would be cheaper and I could put it in my truck in the warmth of my garage this winter, the boat has to sit outside until I can afford a pole barn large enough.