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Discussion Starter · #1 · (Edited)
I'm working on a 4BT swap into my 1994 Jeep Wrangler YJ. I use this vehicle as my daily driver and love the open air driving. For the past 10 years, I've toyed with the idea of building a Jeep Wrangler that suits me. With the rising costs of gasoline and the pathetic fuel mileage the Jeep was getting. I began searching for alternative engines. My goal was to do a cost-efficient build and acheive the best fuel mileage I can get. I stumbled accross someone else who swapped in a Cummins Turbo Diesel. I was hooked. I began searching everywhere I could for information. And, I eventually subscribed to the Yahoo groups. Then, I joined here when it moved.

This thread has been almost like a journal of my build. I hope others considering their projects can use it when planning their build. It's kind of my exchange to the 4BT community for the information I've received from them. The swap, for me, wasn't just tossing in another engine and transmission. I also had to upgrade the drivetrain components to match. Each of those components was yet another swap itself I had to acquire information for and consider how they would perform together.

With all of that information floating around. It was easy to lose or forget it. I ended up making what I call my "Build Bible". It's a binder with partitions labeled "Donors, Engine, Transmission, Transfer Case, Front Axle, Rear Axle, Brakes and Other". All of the information with regards to each conmponent swap I could find was printed and organized into their repective sections. It was invaluable while I was working on multiple swaps and trying to keep everything straight.

I've also tried to include some of costs involved. It's easy for me to forget how every little thing adds up. I've seen more than a few guys on here and other places tell people to "Take those costs and double them". That is not the case here. I think I allowed $3500.00 for the swap. My costs are over double that and still going.

The build-up is complete. So, I'll post up my test driving experiences, fuel mileages, and maintenance history. My goal here is to give anyone interested a complete up-to-date account of my 4BT experience. So here goes!
 

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Discussion Starter · #2 · (Edited)
Fuel Consumption Log

I'm going to try and incorporate an up-to-date fuel consumption log here. I will post my entries here for an at-a-glance overview. I will also post a reply entry at the end of the thread to keep it up to date and to provide discussions between fuelings.

Year - MPG
2007 - 17.24
2008 - 17.53
2009 - 17.36​

Overall MPG: 17.38

To review any notes or discussions with regards to each entry, you'll need to go the appropriate time period on the thread.
 

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Discussion Starter · #3 · (Edited)
Cost Overview

Expenses:
  • 5,500.00 - 1994 YJ Wrangler, 4.0-6cyl, Auto - 170,457 Miles
  • 1,972.00 - 1988 Chev P30, Cummins 4BT, GM-TH400 - 65,253 Miles (since rebuild)
  • 1,841.47 - 1982 Jeep Wagoneer - Dana 44 Front Axle
  • 1,622.27 - 33"x15.5"x15" Tires & 15"x10" Wheels
  • 1,549.50 - TH-400/NP231 Transplant
  • 1,480.60 - Chassis Preparation
  • 1,350.54 - 1995 Ford Explorer - Ford 8.8 Rear Axle
  • 0,809.88 - Heat & Engine Cooling
  • 0,268.57 - Rear 5-to-6 Lug Adapters
  • 0,254.11 - HydroBoost Brakes
  • 0,242.79 - Filters, Fluids, Intake & Exhaust
  • 0,142.54 - Driveshaft Modifications
  • 0,061.28 - Miscellaneous
Income:
  • 1,271.20 - Recycling P30
  • 0,586.33 - Unused Parts
Net Cost: 15,238.02

Upgrades:
  • 0,792.12 - HY35W Turbo

To-Do List:
March 2011
  • Install HY-35 Turbo​
  • Install EGT Gauge​
  • Install Boost Gauge​
  • Install KSB Switch​
  • Install 3200 Gov Spring​
  • Install Air Horns​
  • Install SYE Kit​
  • Rebuild Transfer Case​
Later


  • SOA Suspension Lift
  • Fuel Pin
  • Optimize Pump & Injectors​
  • Install FilterMinder​
  • Install Cruise Control​
  • Install Spare Tire & Cover​
  • Recover Driver's Seat
Read on for the Build-Up
 

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Discussion Starter · #4 · (Edited)
The Beginning!

On Saturday, April 21, 2007, we started disassembly.
  • The engine and transmission have been removed from the donor.
  • The wrangler has the body off and the frame has been stripped of the suspension.
  • I just purchased the Ford 8.8 rear axle to be swapped in as well.
On April 24th - I weighed the both engine and transmission combinations at a Certified Scale.
  • The orginal Jeep 6cyl engine and Auto tranny weighed in at 640lbs.
  • The Cummins 4BT and GMTH-400 Combo weighed in at 920lbs.
  • There's 280 lbs of additional weight mid to front to compensate for.
Today, I got my adapter parts from Novak-Adapt.com to mate the TH-400 transmission to the NP231 transfer case. I ordered:

SS231 - Spacer Seal - 17.68
RMU - Rear Transmisison Mount1 - 35.50
41 - 23 Spline Adapter - 459.00
Shipping - 19.79
Total Cost: 531.97

I just recently found this site. I'll post the build-up as I go.
 

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Discussion Starter · #7 ·
As you can probably tell I'm setting the Jeep up primarily for street use. I mostly drive on a highway back and forth to work. So the speed limit is 55. I enjoy the look and open air driving of the Wrangler. From this project, I'm looking for fuel efficiency and a cost efficient build.

I thought long and hard about the overdrive. I would've liked to use a 4L80E with a 3.08 ratio. Let's face it. The transmission is expensive when buying it and a standalone controller unit together. The 400 came from the donor with the cummins. I plan to use the 2.73 ratios to keep the RPMS down to about 1800 while traveling 65 mph on the interstate with 33" tires.

From what I've read, most of the parts are interchangeable between the 2 transmissions. I was thinking the adapter might work with the 4L80E when/if I ever need to replace the TH400. But, I have no confirmation on the adapter interchangeabilty. If not, the adapter will be easy to sell.
 

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As you can probably tell I'm setting the Jeep up primarily for street use. I mostly drive on a highway back and forth to work. So the speed limit is 55. I enjoy the look and open air driving of the Wrangler. From this project, I'm looking for fuel efficiency and a cost efficient build.

I thought long and hard about the overdrive. I would've liked to use a 4L80E with a 3.08 ratio. Let's face it. The transmission is expensive when buying it and a standalone controller unit together. The 400 came from the donor with the cummins. I plan to use the 2.73 ratios to keep the RPMS down to about 1800 while traveling 65 mph on the interstate with 33" tires.

From what I've read, most of the parts are interchangeable between the 2 transmissions. I was thinking the adapter might work with the 4L80E when/if I ever need to replace the TH400. But, I have no confirmation on the adapter interchangeabilty. If not, the adapter will be easy to sell.


I didn't realize you had 2.73's, 1800 should be good. Around town won't be as good as it could be but should be fine. Most of the highways around here have 65mph speed limits. I like to travel in the 70-75 range, not sure how the 4bt will like it, even with OD/3.55's/31's.

oh, and that adapter should be just fine for a 4L80E, I thought about that route as well, but they are SO much $$ to get working correctly. I am hoping i can get the 700r4 i have to hold up, we'll see.
 

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Discussion Starter · #10 ·
I didn't do anything over the weekend with this project. I worked on some others. Tonight I separated the 4BT and TH-400 so I can send off the transmission off tommorrow to get fitted with the input shaft from Novak adapters.

I also finished stripping the frame of its components so it can get sandblasted, primed, and painted. The frame really needs a rear crossmember that holds the gas tank up. The current one is pretty thin and eaten though due to rust. I guess I'd better get to work trying to find one of those.
 

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Looks good. I wish I had done the motor swap before the body work so I could take it down to the frame. Should be a good fun project with LOTS of satisfaction!

A lot of the late 60s to early 70s cadillacs had 3 to one rearends. With the torque of the 472 and 500, they still did burnouts. You should be fine with a lower vehicle weight and a torquey motor.
 

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Discussion Starter · #13 ·
In the very first conception of this project, I planned on using a 700R4 transmission. I've had several vehicles with that transmission. I think it is a very good and solid transmission. However, I just did not feel the transmission would be up to handling the engine for the period of time I intended without being modified.

The TH400 came with the engine and was already there. I wanted to capitalize on the torque and the engine puts out by using the ring and pinion choice I made. And, to be frank, I was curious to see how well this combination would work.

I also think using the TH400 put me in a good position for a possible 4L80E swap in the future. But, that project will be a long way off and will go though a lot of refinements along the way.
 

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Looks like a great project! I'm doing just about the same thing you are with the transmission/axles in my CJ project. I'm going to be ordering the TH400 to Dana 300 adapter from Novak as well. I managed to score a set of factory wide track CJ axles with a 3:31 ratio and factory limited slip. I'm going to be stepping up to 35" tires so we should be in the same ball park as far as RPM's vs. top speed goes. I'm going to keep an eye on this thread for sure. Keep up the good work!

MIke
 

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Discussion Starter · #15 ·
Hey guys! Thanks for reviewing this thread. I know I've looked at your posts in the past (well I still do) when I was researching this project. As you can see, I've been using this thread as kind of a journal of my build. I also hope others will be able to use this thread in determining the course of their own build and what works best for them.
 

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Discussion Starter · #16 ·
I dropped off the transmission to have the input shaft installed.

I also dropped off both axles to have 2.73 ring and pinions installed. The mechanic noted the Ford 8.8 sits off center a lot and questioned whether it would work for me. As soon as I got home, I looked other Ford 8.8 swaps. I did find the pinion sets off 2-3/16" to the right of center. I'll go back tommorrow and do a quick measurement to verfy my axle has the same offset. The salvage yard handed me a receipt showing it came from a 95 Ford Explorer.

I also won an ebay auction for a lightly used Posi-Lock cable to replace the vaccum disconnect on the Dana 30 front axle. Cost was 123.50 + 15.00shipping.

One thing I haven't figured out yet is what I should do in the front springs to handle the extra 280 lbs. of engine.
 

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I dropped off the transmission to have the input shaft installed.

I also dropped off both axles to have 2.73 ring and pinions installed. The mechanic noted the Ford 8.8 sits off center a lot and questioned whether it would work for me. As soon as I got home, I looked other Ford 8.8 swaps. I did find the pinion sets off 2-3/16" to the right of center. I'll go back tommorrow and do a quick measurement to verfy my axle has the same offset. The salvage yard handed me a receipt showing it came from a 95 Ford Explorer.

I also won an ebay auction for a lightly used Posi-Lock cable to replace the vaccum disconnect on the Dana 30 front axle. Cost was 123.50 + 15.00shipping.

One thing I haven't figured out yet is what I should do in the front springs to handle the extra 280 lbs. of engine.
i'm sure your 8.8 is fine, they are all pretty offset. only issue it can really cause is exhaust interference, nothing too bad.

why did you bother with the cable lock instead of just putting a one-piece shaft inplace of it? the cable is better than vacuum though.

maybe just add some leaves to the front springs? have you talked to the guy selling the 4bt YJ on ebay?
 

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Discussion Starter · #18 ·
I measured the Ford 8.8. I have the correct axle. I just doubted myself.

For the front, I opted for the manual disconnect cable because mainly because I just didn't do enough research to see I could swap in a one-piece axle in place of the original 2-piece. Thank you for the suggestion DieselDurango. Those axles aren't back yet and I'll do some more research on that.

I also dropped off the front leaf springs today. The shop working on them in Indy are planning to add a leaf to each side. They should be done by the end of the week.
 

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sounds good, i think to put a one piece shaft in you will need a block off plate and some seal work. i know the info is out there, i just haven't done it myself. someone probably sells a kit to do it.

What kind of lift are you doing? Keeping it spring under? I would find a way to truss that dana 30 if you can, even one of the aftermarket trusses would probably be a good idea. There will be a lot of extra weight on it.
 
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