Cummins 4BT

Jeep2010

New member
Alright ladies and gentlemen, it's about that time. I'm getting a Cummins next month and going to start rebuilding it slowly but surely. This topic hopefully sheds some light on things I may have over looked. I'd like to hear concerns some of you may have with the swap. If you're curious about the "build sheet" of the engine I'll type it out. Certain things are still in the works about it. But let's hear all the concerns about it! I know I'm over looking something and want to be sure before I drop it. Thank you in advance!
 
I always thought these were cool until I actually went on a trail run with other jeeps and realized how awful it would be to have a diesel in the mix. The noise and fumes would piss me off. If you spent most of your time going up and down the highway it's probably a good choice though.
 
It's a daily driver for me but at the same time I'll wheel it. The guy I'm buying the engine from has one in a tj and it wasn't as bad as I thought but it is louder for sure. But I don't wheel as much as I'd like to just because the trails around me in Ohio is somewhat limited.
 
Just don't cheap out on good mounts. Cummins, the 4bt especially, are known for vibrating a lot. And you'll catch a lot of flak for it because the 4bt weighs like 900lbs and people don't understand why you'd want something so heavy. I on the other hand have driven many Cummins powered vehicles and have a friend who swapped a 4bt into a gmc sprint with k5 suspension and axles. You'll see mpgs you never dreamt of! I'm here for updates.
 
I've got an FJ40 with a 4BT in it. It is a cool project vehicle and it gets a lot of attention so if that's what your after I would recommend it. If your after a trail rig and daily driver like you mentioned I would recommend going another route, maybe doing a V8 swap like so many others have done to their JK's. Like mentioned above, the 4BT vibrates ALOT, smokes ALOT, and is very loud.

When I say it smokes it doesn't poor out soot like some of the :asshat: kids have with over-tuned diesel trucks, but the exhaust fumes from the 4BT are very strong/potent. Mine runs very well, and will only poor very light soot when under heavy load, but even though you may not be able to see the exhaust, you will most definitely smell and taste it. Your friends will not want to wheel with you and after the honeymoon wears off with your 4BT you probably won't want to yourself. Obviously decent speed and wind helps eliminate the exhaust issues for those around the vehicle, but not so good for a slow trail machine.

The vibrations are a lot for the FJ40 which has zero plastic interior parts. The only plastic interior parts it has are speakers, which by the way are a waste because you won't be able to hear them, and I have had to replace them a couple times because the vibrations make them fall apart. Unless you plan on removing all the cheap plastic interior from your Jeep the 4BT will do it for you. The vibrations are at a fairly fast frequency and can be numbing if you drive it for any extended periods. You may be able to fab a special engine mount to prevent some vibes, but keep in mind these engines were put into very large trucks with large frames and bodies which absorb and dissipate a lot of the vibes from the engine. Our little jeeps, and my little FJ not so much. For reference I have the mounts out of the truck it came in on the FJ.

Another thing is this engine has a ton of instant torque. Prepare to break Jeep parts. If you don't have ton axles in the budget that's another thing you have to consider.

Another consideration is you will not get great highway speeds with a 4BT. Granted I could probably gear a little better for highway use, but you may want to drive your friends TJ on various roads and freeways to be sure you'll be happy with it. I have no top end and can't use the FJ on the freeway at all. At higher speeds I can floor it and almost nothing happens.

Suspension will be another issue. The 4BT is a pretty heavy engine so whatever springs your running will have to be changed out for heavier rated springs.

It does get great fuel mileage though. Hand calculating I am in the 40 mpg range, but this is at 40 miles per hour on small farm roads.

If your Jeep is a second, third, fourth (or more) vehicle for you and your family then it might work out. Mine is a fifth and last to get driven for fun every once in a while. If it is your daily driver then in my opinion you would be making a huge mistake.

Don't mean to be a stick in the mud, just want you to be well aware of what my 1st hand experience with my 4BT is.

If you do end up going through with it, I hope you'll do a detailed build thread because it will be fun to watch. :thumb:
 
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I've got an FJ40 with a 4BT in it. It is a cool project vehicle and it gets a lot of attention so if that's what your after I would recommend it. If your after a trail rig and daily driver like you mentioned I would recommend going another route, maybe doing a V8 swap like so many others have done to their JK's. Like mentioned above, the 4BT vibrates ALOT, smokes ALOT, and is very loud.

When I say it smokes it doesn't poor out soot like some of the :asshat: kids have with over-tuned diesel trucks, but the exhaust fumes from the 4BT are very strong/potent. Mine runs very well, and will only poor very light soot when under heavy load, but even though you may not be able to see the exhaust, you will most definitely smell and taste it. Your friends will not want to wheel with you and after the honeymoon wears off with your 4BT you probably won't want to yourself. Obviously decent speed and wind helps eliminate the exhaust issues for those around the vehicle, but not so good for a slow trail machine.

The vibrations are a lot for the FJ40 which has zero plastic interior parts. The only plastic interior parts it has are speakers, which by the way are a waste because you won't be able to hear them, and I have had to replace them a couple times because the vibrations make them fall apart. Unless you plan on removing all the cheap plastic interior from your Jeep the 4BT will do it for you. The vibrations are at a fairly fast frequency and can be numbing if you drive it for any extended periods. You may be able to fab a special engine mount to prevent some vibes, but keep in mind these engines were put into very large trucks with large frames and bodies which absorb and dissipate a lot of the vibes from the engine. Our little jeeps, and my little FJ not so much. For reference I have the mounts out of the truck it came in on the FJ.

Another thing is this engine has a ton of instant torque. Prepare to break Jeep parts. If you don't have ton axles in the budget that's another thing you have to consider.

Another consideration is you will not get great highway speeds with a 4BT. Granted I could probably gear a little better for highway use, but you may want to drive your friends TJ on various roads and freeways to be sure you'll be happy with it. I have no top end and can't use the FJ on the freeway at all. At higher speeds I can floor it and almost nothing happens.

Suspension will be another issue. The 4BT is a pretty heavy engine so whatever springs your running will have to be changed out for heavier rated springs.

It does get great fuel mileage though. Hand calculating I am in the 40 mpg range, but this is at 40 miles per hour on small farm roads.

If your Jeep is a second, third, fourth (or more) vehicle for you and your family then it might work out. Mine is a fifth and last to get driven for fun every once in a while. If it is your daily driver then in my opinion you would be making a huge mistake.

Don't mean to be a stick in the mud, just want you to be well aware of what my 1st hand experience with my 4BT is.

If you do end up going through with it, I hope you'll do a detailed build thread because it will be fun to watch. :thumb:

I have thought of some of these. I know I've been talking to river raider about which mounts they used for their 6bt conversion and having them adapt it for a 4bt and other companies. From what I can recall off hand about the mounts it's two mounts for it. I can't remember the specific name of it but it was something along the lines of a hydro mount or something. I could be wrong on the name but they were saying it'll dampen the Cummins a bit. Not completely but anything helps. The guy has a tj with one in and he said I can drive his and that's what I'll base it on. This is my only vehicle right now, but when this gets put in, it wouldn't be my only vehicle. I have built my axles a bit. I have an aftermarket front 44 and stock 44 and would like to go to a 60 anyways so if it breaks I'm not too worried about it. But this is why I put the topic up, it's nice that you have one and I've heard a lot of mixed reviews about them and ultimately need to drive one. I've driven an s10 with one in and it wasn't terrible but I'm trying to build it to be good for my application. I don't want to be scared to drive it but I don't mind it being what it is either. If that makes sense lol.
 
Ctimrun
That has got to be the best description of life with the 4bt I have read.
You about had me in tears from laughing so much.
Spot on accurate.
Good motor, for a tractor.

OP please look at V8 swaps. You will be so much happier.
 
What's wrong with the motor that is in it now?

Just getting high in miles. I'm not planning on dropping it right away. I just want to rebuild it and get everything ready for when mine does get in its last leg. I got it in December of 2010 and I'm pushing 160k and in driving more lately.
 
I've got an FJ40 with a 4BT in it. It is a cool project vehicle and it gets a lot of attention so if that's what your after I would recommend it. If your after a trail rig and daily driver like you mentioned I would recommend going another route, maybe doing a V8 swap like so many others have done to their JK's. Like mentioned above, the 4BT vibrates ALOT, smokes ALOT, and is very loud.

When I say it smokes it doesn't poor out soot like some of the :asshat: kids have with over-tuned diesel trucks, but the exhaust fumes from the 4BT are very strong/potent. Mine runs very well, and will only poor very light soot when under heavy load, but even though you may not be able to see the exhaust, you will most definitely smell and taste it. Your friends will not want to wheel with you and after the honeymoon wears off with your 4BT you probably won't want to yourself. Obviously decent speed and wind helps eliminate the exhaust issues for those around the vehicle, but not so good for a slow trail machine.

The vibrations are a lot for the FJ40 which has zero plastic interior parts. The only plastic interior parts it has are speakers, which by the way are a waste because you won't be able to hear them, and I have had to replace them a couple times because the vibrations make them fall apart. Unless you plan on removing all the cheap plastic interior from your Jeep the 4BT will do it for you. The vibrations are at a fairly fast frequency and can be numbing if you drive it for any extended periods. You may be able to fab a special engine mount to prevent some vibes, but keep in mind these engines were put into very large trucks with large frames and bodies which absorb and dissipate a lot of the vibes from the engine. Our little jeeps, and my little FJ not so much. For reference I have the mounts out of the truck it came in on the FJ.

Another thing is this engine has a ton of instant torque. Prepare to break Jeep parts. If you don't have ton axles in the budget that's another thing you have to consider.

Another consideration is you will not get great highway speeds with a 4BT. Granted I could probably gear a little better for highway use, but you may want to drive your friends TJ on various roads and freeways to be sure you'll be happy with it. I have no top end and can't use the FJ on the freeway at all. At higher speeds I can floor it and almost nothing happens.

Suspension will be another issue. The 4BT is a pretty heavy engine so whatever springs your running will have to be changed out for heavier rated springs.

It does get great fuel mileage though. Hand calculating I am in the 40 mpg range, but this is at 40 miles per hour on small farm roads.

If your Jeep is a second, third, fourth (or more) vehicle for you and your family then it might work out. Mine is a fifth and last to get driven for fun every once in a while. If it is your daily driver then in my opinion you would be making a huge mistake.

Don't mean to be a stick in the mud, just want you to be well aware of what my 1st hand experience with my 4BT is.

If you do end up going through with it, I hope you'll do a detailed build thread because it will be fun to watch. :thumb:

I second ctimrun. I had a 4BT in my old power wagon and it was good for gas mileage. But I topped out at 65mph (had 37" tires and 4.88 gears with an NV4500). Broke the stock axle shafts twice before upgrading the axle. Vibrated and shook like crazy. Was fun and drew lots of looks. But if I was to do it over would do a V8
 
I second ctimrun. I had a 4BT in my old power wagon and it was good for gas mileage. But I topped out at 65mph (had 37" tires and 4.88 gears with an NV4500). Broke the stock axle shafts twice before upgrading the axle. Vibrated and shook like crazy. Was fun and drew lots of looks. But if I was to do it over would do a V8

What was the rpm with it?
 
I guess I didn't mention that my top speed on the FJ is about 55 but that is max speed downhill with a tailwind. Actually wouldn't matter if I was going uphill with a headwind, it would still do about 55. Don't quote me on this as I would have to look it up to be sure, but I believe the redline of most 4BT engines is about 3000 RPM's but they will start to de-fuel well before that, probably around 2800 RPM's. The engine can be run at that RPM probably forever without hurting it, but when you hit that RPM limiter it is like hitting a wall. If for some reason your RPM's were to get past your limiter the engine will start to come apart in the high 3's/low4's. I am remembering that from years ago so that may not be entirely accurate, but you get the idea. Just know the RPM limits are pretty low with the 4BT.

Also the 4BT's have a bad habit of leaking oil wherever you are. That's right, wherever you go you will leave a trail. I have been and am still working on this but it is very low on my priority list. I will probably always keep two large oil catch pans under it to prevent damaging my garage/shop floor.

My wife was just looking over my shoulder so we talked FJ for a second and she wanted me to remind you that she doesn't even like me to start it up in the garage to pull it out, especially in the winter. It will smoke out the garage and the house if I don't immediately put it in gear and get away from the garage. Sometimes (when she is home and paying attention) I will take it out of gear and roll it out of the garage, close the garage door, then start it up. My wife is a great sport and loves driving it, just doesn't like the exhaust smell especially in the house, lol.

IF I were going to put an engine in my JK, to keep its manners acceptable I would seriously look into a Hemi (if I wanted to keep with the Mopar theme) or go with the 6.0/6.2 GM engine which is what Eddie has I believe. I would probably go with what Eddie has because he is so good about sharing all of his knowledge and experiences with all of us. Why try to reinvent this? Headaches I wouldn't want and don't have time for.
 
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Would do 60 when I had 35" tires.
Same thing with my wife about starting it up. Smoked the whole house up.
 
It'll tear itself apart at 4250 and redline is depending on how the engine is built/rebuilt. But I don't see the value in a V8 personally. Unless someone is willing to tell me an actual cost for swapping in a V8 and the power they are getting out of it.
 
It'll tear itself apart at 4250 and redline is depending on how the engine is built/rebuilt. But I don't see the value in a V8 personally. Unless someone is willing to tell me an actual cost for swapping in a V8 and the power they are getting out of it.

Someone else with V8 swap experience will have to answer this for certain, but IMO the V8 makes the Jeep more fun to drive to and from trails and everyday driving duties. If your looking for something for trail only use you would probably be a lot better off by getting a replacement Jeep V6 and putting your money, time, and efforts into your suspension, axles, tires, etc. I'm too busy to be a hard core rock crawler but I haven't heard too many complaints about the stock engine on the trails, more drivetrain complaints.

Whatever swap you decide I look forward to reading about it. :thumb:
 
It'll tear itself apart at 4250 and redline is depending on how the engine is built/rebuilt. But I don't see the value in a V8 personally. Unless someone is willing to tell me an actual cost for swapping in a V8 and the power they are getting out of it.

I can't tell you cost. But if you have the engine already and you want to do it. I look forward to reading about it and seeing how it goes for you
[emoji106]
 
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