Loo king into diesel swap

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Bigpete1
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Loo king into diesel swap

Postby Bigpete1 » Tue Aug 23, 2016 11:01 pm

:fsj: Hello everyone new to the whole forum and FSJ world sorry if it's a repeated post!!. I bought my first 73' fsj. 4 months ago and looking into doing a swap I've seen alot of people who are going the 4bt/6bt route I live in SoCal and anything older than 75' is smog exempt so that is no issue for me . I have the OG 360 motor and turbo 400 trans it is currently my daily driver so gas is killing me expected of course. So my question(s) are can I swap either 4bt/6bt with adapter over to my tranny and have it work or is it recommend to swap motor,transfer, trans,and axles out to be able to handle the power. Building it up to remain my daily driver and also trail rig mud :fsj: rock whatever really. Thanks in advance for your time and wisdom !!! Also takes me awhile to respond I drive for a living and work 10-12hrs a day. But that's life

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Stuka
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Re: Loo king into diesel swap

Postby Stuka » Wed Aug 24, 2016 9:48 am

First, welcome!

Second, if its your daily driver, can you actually go without driving it for the time that the build takes?

As for which engine, the 6BT requires extensive firewall modifications and an axle swap, as your D30 would in no way support an 1100lb engine. Even the D44 used in later years is not up to it.

A 4BT is lighter, but still heavy, so still really need a beefier axle. And I do not know of an adapter that will go to an AMC pattern. You would need to look into using a different trans housing at least (like GM TH400 housing using your guts or the like).

Another option is to go with a GM 6.2/6.5L diesel.

Then you just need to weigh is doing a rather expensive swap worth what you will save in fuel.
1981 J10 AMC 258 with HEI and Weber 32/36 DGEV Carb, T176, NP208, D44/M23 with 4.56 gears and Detroit Locker, 6" lift, 33x12.50 Cooper STT's, BJ's Offroad Rear Dozer Bumper.
2017 JKU Rubicon Stock, but not for long!
Pevious Jeeps: 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ

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Pablo
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Re: Loo king into diesel swap

Postby Pablo » Wed Aug 24, 2016 6:39 pm

I wouldn't keep the th400 for either a 6bt or a 4bt. The th475 comes stock behind some 4bt's and barely survived stock power levels. Turning the power up will require a heavily built th400 and a custom torque converter (diesel specific with a lower stall). Still no overdrive, so your fuel mileage will not be optimal, unless you gear numerically low. If you do, then your 4x4 crawl ratio is poor. Much better off finding an overdrive automatic and tranfercase along with the motor.

When choosing between the BT series keep weight and center of gravity in mind. The 6bt is heavy (1200+ pounds) and both have a higher center of gravity than a gasser. If care is not taken in mounting, you can end up with a squirrelly rig that tips over too easily when wheeling. The 6bt will also be front heavy and want to sink into the mud much more.

You can also have clearance issues if you are not running a lift of some sort. The oil pan can hit the axle. I switched the oil pickup to the other side and flipped the pan around to clear my axle better. I am SOA with no body lift and cut sheet metal on a 1965 Wagoneer, so your mileage will vary.

There are alot of hidden costs with the diesel route. I cost justify it by building up the entire vehicle to be the expendionary vehicle I want. It is then cheap, compared to a new custom diesel or a 4x4 van/wagon.

It would be much cheaper to just throw a vortec 4l80e or a Toyota power train from a land cruiser in and move down the road.

Bigpete1
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Re: Loo king into diesel swap

Postby Bigpete1 » Thu Aug 25, 2016 12:10 pm

I would be able to get around as far as build time I also had considered vortec. But heard that it just eats threw the fuel. I guess im still on the wall as far as what is better to swap it out with. I was leaning towards 4bt and swapping it all out trans, transfer, axles. Witch seems like what's going to end up happening thanks for the info I appreciate it.

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Stuka
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Re: Loo king into diesel swap

Postby Stuka » Thu Aug 25, 2016 12:32 pm

I would not expect good mileage, regardless of the engine. FSJ's have very poor aero.

Also note that the 4BT is kind of a harsh engine. Quite a bit more vibration than most engines.
1981 J10 AMC 258 with HEI and Weber 32/36 DGEV Carb, T176, NP208, D44/M23 with 4.56 gears and Detroit Locker, 6" lift, 33x12.50 Cooper STT's, BJ's Offroad Rear Dozer Bumper.
2017 JKU Rubicon Stock, but not for long!
Pevious Jeeps: 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ

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tedlovesjeeps71
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Re: Loo king into diesel swap

Postby tedlovesjeeps71 » Thu Aug 25, 2016 4:21 pm

If one uses a 4bt and wants to go with a manual transmission, how is this done considering the factory 4sp is so long? Is it possible to use something like an nv4500?

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Pablo
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Re: Loo king into diesel swap

Postby Pablo » Thu Aug 25, 2016 4:35 pm

tedlovesjeeps71 wrote:If one uses a 4bt and wants to go with a manual transmission, how is this done considering the factory 4sp is so long? Is it possible to use something like an nv4500?

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You are going to have to move mounts around and probably switch transfer cases and drive shafts. I would swap out the whole drive train if going Cummins. Nv4500 is a great choice, or a ZF5 4x4. The cost to use a certain transmission will depend on the 4bt bellhousing the engine has on it, they have different Bell housings. Buying an engine with the housing for the transmission you want may save you money. You can swap the housing out to a different one, but that is more money for the housing/adapter.

My 4bt had a small block Ford housing with a t-19 behind it, so I went with the zf5.

You may also have to decide if you want to have your drive train and transfer case a bit lower than the frame rails, or if you want the motor mounted higher and the transmission tunnel raised up. I got the motor as low as I could and have an inch and half to two inches hanging out below.

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eggman918
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Re: Loo king into diesel swap

Postby eggman918 » Thu Aug 25, 2016 7:13 pm

A 4BT with the right turbo and gearing 20 MPG + should be attainable I'm seeing that in my '68 F-250 crewcab that is 8,000# empty, but i'v done a bit of tweaking to the VE injection pumps dynamic timing advance and had the injectors rebuilt with stock tips which run clean at the 200 hp level...$.02
1967 Wagoneer soon to be TDI powered
1968 F-250 CrewCab Cummins 4BT, ZF-5, NP 203/205,TruTrac's front/rear.


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