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Ok this is my first time posting on this site. I’ve been reading a lot of forums to try to get a better understanding of doing a diesel swap. I’m not ready for the swap yet and this is more of looking for more clarity on what direction would be best to take for what I want to use the truck for. It was an ex military/ fire department truck has 9000 original miles never put on the road since put in private hands. I am wanting it to use on my property and go down the highway as well no huge trailer pulling. A mix of good MPG and highway speeds 60 to 65 is where I’m at. It is all stock. I currently own a Bobbed M35a2 so no stranger to the work that will be involved. I will have the truck home between now and March.
I have a 1968 W300 sweptline with 6BT & NV4500 Dana 80 rear dana 60 front with ORD crossover steering Hummer tires & wheels 4:11 gears works nice & I have put around 6000 miles on the truck tuned to pull a trailer with '47 WDX on it. W300 weighs 8400 with me in it. that is a lot for a 4bt if you need any more info just ask Ron
 

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Discussion Starter #22
Ya I’ll definitely have a lot of questions for you as you’ve done this swap already especially engine clearance motor mounts and power steering
 

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Like Red mentioned, there are 5831 transmissions with different OD ratios. The one with the .73 would be much better with your 4.88 axle. What are the tire size on the old Dodge? Might be able to work out a combo to avoid axle gear change. You want to try to keep engine speed under 2000 RPM for general road driving for best fuel economy. Also, a Cummins peak torque is in the 1700-1800 RPM area. Drops off pretty steeply as you pass 2000 RPM.
 

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Discussion Starter #24
I would probably be in the 35”to 37” tire range. I don’t want to go any wider than 10”. I have only 2 options for wheels the stock 17.5s or custom made wheels because of the lug pattern. The companies that made some of the aftermarket stuff such as brakes and wheels are no longer in business or no longer making them. I am very skeptical of using Stockton Wheels because they have a lot of bad reviews especially with customer service and fixing mistakes. I am still weighing in on an axle swap but still want to keep an old school look to the truck. I want as far as MPGs hopefully over 15.
 

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If you go with 17.5 you won't have much issue with the width. There are only a few sizes of that tire available. I believe the largest is the 235/75R17.5 which are around 36" diameter and about 9.5" wide. Most all those are 14 or 16 ply. Not sure how smooth the ride would be. With that tire and a 4.88 gear your engine would be turning 2734 RPM @ 60 MPH in 4th gear. With a .73 OD you'd be at 1996 RPM which is ideal. If you changed your gears to 4.10 you engine speed would be 1677 RPM would is super fine. That way, if you wanted to cruise at 70 MPH you'd be at 1956 RPM. The Cummins would love that gear with that tire size. Of course all that depends on getting the transmission with the .73 OD.
 

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Discussion Starter #26
I have been reading a ton online I am looking at having wheel adapters made for it got a quote of around 700$ to adapt 8 lug wheels USA made not some overseas dangerous junk. Thinking of running a 20” tubeless wheel with a tubed tire tubeless. I’m looking at 8.25-20 which would be 39” tall. The thought here is to keep most of my drivetrain stock less work less money. Plus makes finding a parts truck easier and cheaper as long as it’s a stick shift and an nv4500 or something similar.
 

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Discussion Starter #27
I also wanted to add that the stock tire are around 31.5” and the stock wheels have a negative offset. So I would want to add a body and suspension lift. The body lift would also add clearance in the engine compartment for the 6bt so I would benefit from both. This is still just an idea at this point.
 

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Of course you might also consider just changing the axles to something more modern. You'd have modern brakes, a vast selection of wheels, and tons of gear ratios.
 

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Discussion Starter #29
I thought of that as well but would depend on what I can find for a parts truck. Axles alone are expensive vs a parts truck and extra work to install them. It will come down to what I can find and over all cost and work but definitely not off the table.
 

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Discussion Starter #30
I have found a wheel I really like that would go with the look I am trying to go for on the truck from Black Rhino Armory but they are only available in 17” 18” 20”. I have not found a tire pattern I care for in 17” or 18”. They all look too modern I’m just not a fan of BroDozers LOL. If they were made in 16” I’d be golden but only in 20” can I find a retro style tread pattern. I looked at trucks with 40” tires as that’s as close to 39.5” I could find to look at the ride height to see if it would work or be too tall to make the truck usable for work here on my place daily driving and some hauling. They didn’t look too bad from what I looked at I also want narrow tires ,wide tires would just take away from the look plus put more scrub when steering and drag over all. I wonder how tall I’d have to go to put narrow 39.5 tires on it?
 

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If you start thinking tires that are 39.5 then you have one as big or bigger than some semi truck tire. 235/R70x22.5 is only 36.56". A 10R22.5 is like 40". Might look a bit oversized on that truck. You could get adapter plates and install Alcoa wheels. That would put a pretty big dent in the budget. They might even have models that fit your axles without adapters.
 

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I personally would want a 6bt(cheaper too), but a 4bt will do the job. Firewall can be modified if youre handy with sheetmetal. 3053a is a good trans but have a bad 3rd to 4th spread for turbo. A close ratio ESO would be better for diesel. High teens low 20mpgs should be possible. Dodge 1st gen area. What is weight of vehicle? Dont rule out the zf 6 speeds, they are good transmissions but pricey. You should be able to pick up a SAE3 flywheel at a 1/4(1000) if you do some scouting before build.

Cummins FLYWHEEL 4939064 | eBay 1/2 price
Thank you for the diagram just wondering if it’s worth it with having to add more bracing to the frame to cope with the torque of the 6bt or if tuning a 4bt would be ideal won’t need more than about 160hp to 175hp. The gear ratio for the type of Dana 70s I have that I can go to are 4.10s anything else I’ll have to swap out the axles. I have thought a lot on this because the axles in mine particularly the front axle is almost identical to the stock M715 axles. There is no longer any disc brake conversions being made for them. So definitely have a lot of decisions to make once I get to that point.
I wouldn't think you would need to brace the frame if you use an sae bell housing with side mounts and the front crossmember mount. Really depends on your how your frame is configured now. If you have engine side mounts with a crossmember should be no problem. That np 201 may be strong enough. I assume it's divorce mount why not try it as not much to switch. M715 you mentioned has a closed knuckle Dana 60. Same sized knuckle balls as the 70. (#3500/44 also used large knuckle) I measured a lot of axles years ago and it seems most of the older closed knuckles(maybe open as well, can't remember) have spring perch distance the same. 1974 IH 70 was direct bolt up to 56 PW springs. As i remember the M715/60 also fit(5:38 or 5:88) You might check Chevy closed knuckle 60 or early open knuckle as I recall it was a fit also
 

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Discussion Starter #33
Ya there’s a lot I don’t know about these trucks. I am hoping to lift it some body and suspension wise not way up need it to work . I just hope I can find the lift parts. I am still unsure what tires I want to run but don’t want modern looking tires or wide ones. I want them to look like they belong on the truck.
 

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Ive run the 39/40s. I dont care for them much, they are too wide. Im downsizing to the military 37". Nice height and narrower.
 

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I personally would want a 6bt(cheaper too), but a 4bt will do the job. Firewall can be modified if youre handy with sheetmetal. 3053a is a good trans but have a bad 3rd to 4th spread for turbo. A close ratio ESO would be better for diesel. High teens low 20mpgs should be possible. Dodge 1st gen area. What is weight of vehicle? Dont rule out the zf 6 speeds, they are good transmissions but pricey. You should be able to pick up a SAE3 flywheel at a 1/4(1000) if you do some scouting before build.

Cummins FLYWHEEL 4939064 | eBay 1/2 price
Careful. That outfit has some pretty bad feedback.
 

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I wouldn't think you would need to brace the frame if you use an sae bell housing with side mounts and the front crossmember mount. Really depends on your how your frame is configured now. If you have engine side mounts with a crossmember should be no problem. That np 201 may be strong enough. I assume it's divorce mount why not try it as not much to switch. M715 you mentioned has a closed knuckle Dana 60. Same sized knuckle balls as the 70. (#3500/44 also used large knuckle) I measured a lot of axles years ago and it seems most of the older closed knuckles(maybe open as well, can't remember) have spring perch distance the same. 1974 IH 70 was direct bolt up to 56 PW springs. As i remember the M715/60 also fit(5:38 or 5:88) You might check Chevy closed knuckle 60 or early open knuckle as I recall it was a fit also
I don't think any frame strengthening would be needed even is utilizing the engine center mounts. I have a one ton frame, but I am using the standard frame-size engine mounts that would be used for a SB, BB, or 6.2 diesel. On top of it, my tube motor mounts are fairly minimalist and none of the material is heavier than 1/4". The tube used in the mounts is 1-½" x .120 wall 4130. The frame itself has a material thickness of around .240". Even with a 12V sitting atop it and spending plenty of time getting bounced around off-road as well as a LOT of on-road miles, the frame and mounts are perfectly fine. I think a lot of guys grossly overestimate the weight of these engines and/or the strength required of the frame and motor mounts.











You do need a decently robust and rigid motor mount though:

 

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Careful. That outfit has some pretty bad feedback.
Personally I have no experience with them, never purchased. Was the only genuine C flywheel that was not chinese. Nice to see you back on forum more frequently, you went dark for a bit
 

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Personally I have no experience with them, never purchased. Was the only genuine C flywheel that was not chinese. Nice to see you back on forum more frequently, you went dark for a bit
I don't either, but after checking their FB I wouldn't buy from them. On or two negatives isn't unusual - some buyers are just never satisfied. But thus guy has a lot of negatives, and for the same kinds of issues over and over.

Yeah, I come and go. Just depends on life, how busy I am, etc. You know how it goes.
 
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