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Old 11-16-2015, 12:13 AM
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4bt

Hello i have a 2003 wrangler x auto and im kicking around the idea of swapping my inline 6 with a 4bt for better MPG. my question is will it bolt up to my stock automatic transmission using an adapter plate?

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Old 11-16-2015, 01:57 AM   #2
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To be honest you'll probably just about break even with fuel mileage. The 4bt is a least 100lbs heavier than the 4.0. Maybe more. Plus the cost of custom fab work would take a long time to recoup Not trying to steer you away. Just adding some insite.

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Old 11-16-2015, 07:05 AM   #3
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Hello i have a 2003 wrangler x auto and im kicking around the idea of swapping my inline 6 with a 4bt for better MPG. my question is will it bolt up to my stock automatic transmission using an adapter plate?
I'd hazard a guess that the 360 ft lbs or so of tq that the 4bt presents in a wall-like curve would eat a 42rle transmission in fairly short order. I don't know of anywhere that makes an adapter for that specific combo. If I were doing a 4bt swap I'd be looking to a 4170e conversion at the least. Maybe somebody here is actually running a 4bt mated to a stock 42rle though and can chime in about whether or not they have any issues.
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Old 11-16-2015, 09:04 AM   #4
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the added weight will also lower your front end, not a good swap IMO. heavy, slow, crazy vibrations, and smells.

aluminum chevy v8, better gas mileage and a lot more fun to drive
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Old 11-16-2015, 10:38 AM   #5
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the added weight will also lower your front end, not a good swap IMO. heavy, slow, crazy vibrations, and smells.

aluminum chevy v8, better gas mileage and a lot more fun to drive
When done right, the vibrations will be just about gone. Better gas milage isn't necessarily true. There's a guy on here running a 4BT in his YJ that gets around 25 MPG on 35s (now 37s) and 4.56 gears (yes he is actually overgeared)

Also, what's considered "more fun" to drive is a matter of opinion.

I will say, though, to properly run a 4BT, it costs alot more than an aluminum V8
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Old 11-16-2015, 01:57 PM   #6
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4bt would be a blast in a jeep. Plus you would get great fuel mileage and the ability to add power is very simple from a mechanical injection engine like that. Wiring would be easier too
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Old 11-16-2015, 02:03 PM   #7
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A lot of people swap in the smaller, lighter, and more fuel efficient VW 1.9L and 2.0L diesels.
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Old 11-16-2015, 06:23 PM
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thank you for all the good info! i found a website that specializes in Jeep 4bt and 6bt swaps JD Jeeps - Diesel Conversions - adapters. they have everything you need its pretty cool.
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Old 11-16-2015, 06:33 PM   #9
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thank you for all the good info! i found a website that specializes in Jeep 4bt and 6bt swaps JD Jeeps - Diesel Conversions - adapters. they have everything you need its pretty cool.
I think it's a cool swap myself. I'm just curious where you found the 42rle to 4BT adapters on that site you linked because I don't see them there. Keep in mind I have a 42rle transmission but it would never stay if I did a swap. It is the weakest link in the chain for sure.
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Old 11-16-2015, 06:45 PM
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what transmission do you recommend?
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Old 11-16-2015, 07:00 PM   #11
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what transmission do you recommend?
I have not done a swap into a Jeep of any kind. Though as I stated earlier, if I were to do a swap it would be either a diesel or GM V8, and the transmissions that come to mind as solid candidates for torque handling and reliability would be 4170e, 4180e, or 4185e most likely.
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Old 11-17-2015, 07:30 AM   #12
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Nv4500
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Old 11-17-2015, 07:54 AM
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now would the transfer case that's on the jeep now bolt up or would i have to buy one that fits
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Old 11-17-2015, 07:59 AM   #14
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now would the transfer case that's on the jeep now bolt up or would i have to buy one that fits
Depending on the transmission you use you could get an adapter setup from Novak (or elsewhere). Novak would run ~$500.

http://www.novak-adapt.com
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Old 11-17-2015, 08:02 AM   #15
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The bottom line though, is that if there isn't anything wrong with your current engine and the only reason you are considering swapping to a 4BT is MPG, forget it. You would recoup your swap costs through fuel savings in about 60 years. lol
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Old 11-17-2015, 08:25 AM   #16
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But if you want to swap to get more power and if it would be more fun (for you to drive) then go for it
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Old 11-17-2015, 08:53 AM
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i found an adapter to fit my transfer case to the NV4500. now does anyone know what Spline the 03 wrangler x transfer case came with? i know that its a 23 spline with the manual trans but is it the same with the auto
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Old 11-17-2015, 09:23 AM
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its not my everyday driver so it would be for fun and it would be pretty cool..lol better gas and more power is just a bonus.
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Old 11-17-2015, 10:10 AM   #19
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Cool! I say go for it. Those 4bt are great engines and a diesel jeep would be awesome.
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Old 11-17-2015, 01:14 PM   #20
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i found an adapter to fit my transfer case to the NV4500
In all honesty, there's a transmission to consider for the swap. The NV4500 is a tough sucker as long as you don't mind a slow shifting manual truck transmission. I was considering one for my old FJ40 to hold up better with its 5.7 swap, but at the time it was out of my budget and also now have my Jeep. If you consider it, try to find early 90s model transmissions out of a Chevy. They have an ultra low 1st gear, however they are extremely desirable and are quick to sell even at a premium.

Otherwise, you can find solid 4wd transmissions for ~$800 and fancy rebuilt reman ones for $1200+
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Old 11-17-2015, 10:09 PM   #21
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I am about 75% done with my 4bt swap and have not encountered any major difficulties other than finding the time to work on it. I went with the heavy Chevy flywheel and a nv4500. I did change output shaft to accept the factory 231. The engine and trans fit perfectly and required no driveshaft changes. The front end did sag about 2 inches and I will probably just replace the front springs to a 6 inch lift set or lower the rear coilovers if I still have the needed travel. I did the swap for the simplicity of a 4bt and off idle torque.
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Old 11-18-2015, 04:07 PM   #22
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I am about 75% done with my 4bt swap and have not encountered any major difficulties other than finding the time to work on it. I went with the heavy Chevy flywheel and a nv4500. I did change output shaft to accept the factory 231. The engine and trans fit perfectly and required no driveshaft changes. The front end did sag about 2 inches and I will probably just replace the front springs to a 6 inch lift set or lower the rear coilovers if I still have the needed travel. I did the swap for the simplicity of a 4bt and off idle torque.
How are you gunna tell us that and not put up some pics. If you have any, you should start a new thread. I'd love to see some pics of that.
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Old 11-18-2015, 04:29 PM   #23
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Sounds interesting although these guys don't think it's too great an idea

http://www.fourwheeler.com/how-to/en...ne-swaps-ever/
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Old 11-18-2015, 04:53 PM   #24
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Have you calculated how many years it will take to recoup the cost of the 4BT conversion from the fuel cost savings? If you took the trouble of doing that, I think you'd drop the idea pretty quickly. There are some reasons that some engine swaps make sense but when the costs of the 4BT conversion are totaled up, doing it for better fuel economy makes no sense to me.
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Old 11-18-2015, 05:27 PM   #25
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There are some reasons that some engine swaps make sense but when the costs of the 4BT conversion are totaled up, doing it for better fuel economy makes no sense to me.
Fuel economy may not be the reason. Some people just like working with a diesel, not to mention the torque and motor reliability. Not saying that there aren't "better" swaps out there, but each is to their own
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Old 11-18-2015, 05:39 PM   #26
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Fuel economy may not be the reason.
Well, this is what he said in his first post...

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im kicking around the idea of swapping my inline 6 with a 4bt for better MPG.
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Old 11-18-2015, 06:45 PM   #27
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Doesn't a 4.7L I6 stroker get better MPG? It's a much easier swap. Lot's of torque.
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Old 11-18-2015, 08:37 PM   #28
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How are you gunna tell us that and not put up some pics. If you have any, you should start a new thread. I'd love to see some pics of that.

Sorry, I really haven't taken that many photos of the build. I always take photos of the tare down so I remember how to put it back together. I did however dig this one up from a few nights back. Please excuse the mess, I plan on cleaning up the shop this weekend and I will take a few more photos.
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Old 11-18-2015, 09:17 PM   #29
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Sorry, I really haven't taken that many photos of the build. I always take photos of the tare down so I remember how to put it back together. I did however dig this one up from a few nights back. Please excuse the mess, I plan on cleaning up the shop this weekend and I will take a few more photos.

Striped down about like I did doing my swap

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Old 11-18-2015, 09:37 PM   #30
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Put a pre-filter like an Outerwears or Unifilter over the top of that K&N which doesn't filter worth a crap. I installed both on my k&n after I discovered how much fine dirt and silica was passing through it and was making its way into my engine.

This was my k&n with both prefilters pulled back. It wasn't long before I got rid of the K&N.
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