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Discussion Starter · #1 · (Edited)
I have a 79 CJ5 thats in real good shape and was thinking about repowering with a 4.3 EFI gas burner and then a buddy showed me a youtube video of a 4bt in a jeep rock crawler. It was love at first sight. I own a charter boat with a pair of 6bt's and needless to say I am very familiar with them. I am posting this get some advice on how to get started. The Jeep has the T-15 tranny.Will that bolt up? What do I look for in a motor? How much welding is involved? How expensive is it after the motor purchase? Do i need to regear? Any advice is appreciated. All I really want to do with the Jeep is a run around truck. No interstate, just a 55mph is just fine. The Jeep is geared with 3.07 right now. Is that too high?
 

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The first part of a successful swap is picking your components and planning how you will use it, and figuring gear ratios.
Proper gear ratios are the key to a good swap.

Start by picking the fastest continuous speed you will drive it, usually on the interstate around 65-75, what ever you set your cruise control at.

Then find out what RPM your engine makes its peak torque, for a 4BT that's around 1600 or so. This speed is the speed (or just higher, not any lower)you want the engine at while in high gear on the highway, it will give best economy and driveability.
There are some considerations and this number may change depending on the use of the vehicle. If the engine is low on HP for the weight of the vehicle the cruising RPM will need to be higher than peak torque RPM.
If you will be pulling a trailer or hauling a lot of stuff again the RPM will need to be higher, usually just a few hundred RPM. If pulling a trailer also consider the direct drive gear and your speed and RPM. It could be that you want to gear for driving empty in OD really close to the peak torque RPM, then when loaded you drop it down to direct and can still maintain a reasonable speed at a comfortable RPM.

Pick tire size.

Then consider the transmission OD ratio, and axle ratios for the available and usable components.
Use this site to calculate what ratios you may need http://www.onlineconversion.com/bigger_tires.htm

Pick your components, then start shopping and swapping.

I have driven thousands of miles in poorly geared vehicles with diesel swaps, and then thousands of miles after properly gearing them, the difference is huge, saves fuel, engine life, time, and frustration.
 

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swap

I am in the same boat, thinking about where to begin.

I have done a couple of engine swaps, but no diesels, just gassers.

I have found out that you can never do enough research/planning. Read everything and ask questions before you begin. Like Grigg said, figure out what you are really going to use it for.

I personally would not use a T-15, I think they would not stand up for a long period of time to the torque of the 4bt. You would be better off getting a heavier duty tranny and adapting that to your transfer case.

From what I have read, you will need to weld some for the engine mounts.

good luck
 
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