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4bt yj?

 
Blizzard460 Blizzard460
User | Posts: 103 | Joined: 04/08
Posted: 05/23/08
09:33 AM

i just picked up a jeep yj. 4 cyl 5 spd aisin ax5 trans. the engine is a bit anemic. a perfect excuse to tell the woman it needs another engine. after my previous deal with the f150 that i was originally going to swap a 4bt into fell through, i was considering a 4bt swap into the new jeep. just wondering how the 5sp thats in it now would hold up. i think its got dana 35 axles in it, however i have been told that theyre not the best. dont wanna make a hot rod out of it, but i do need it to get good mileage. what do you guys think? costs of a good swap arent a factor.  
96 F-250 460 V8, Extended Cab, Short Bed K&N Filter, Crane Cam, Ford Racing aluminum heads, 4.56 diff, Eaton lockers, Hooker Headers and Flowmaster Super 40s, true dual

2004 F-250 6.0 Powerstroke, 4 Door, Short Bed, Lariat, 5 inch MBRP dual outlet exhaust, Banks Big Hoss Bundle Kit

1993 Jeep Wrangler, 2.5 I-4, 30 in. BFG All Terrains, hoping to do a 4bt swap someday...

Proud member of the Blowin' Smoke Gang!

Edward A. Sanchez Edward A. Sanchez
Administrator | Posts: 2112 | Joined: 07/06
Posted: 05/23/08
10:12 AM

Talk to bigorange. He's doing a 4BT CJ.  Smile  

ArizonaPerfect ArizonaPerfect
New User | Posts: 20 | Joined: 07/08
Posted: 07/18/08
10:21 AM

I did the YJ Cummins 4BT swap.  The AX5 in your vehicle will have to be upgraded to a AX15.  AX5 won't survive.  Get a Cummins engine adapter for a Chevy manual trans and an A&A adapter bellhousing to mate an AX15 to a small block Chevy.  Use a late 80's diesel Chevy Suburban clutch and pressure plate.  It will all fit together like it was made for each other!

The rear axle will have to be upgraded too.  I used an 8 3/4 Mopar axle (w/3.55 gears) from a 66 Dodge Charger.  Other than welding on new spring pads and shock brackets the axle fit perfect.  Your vehicle will have to have a 4 inch suspension lift to gain adaquate clearance between the oil pan and front axle.

I also installed all of the cold start aids from a 1989 Dodge truck.  My YJ now has a "wait to start" light, intake manifold grid heater, fuel heater, block heater and a water-in-fuel light.  Drove it all winter here in Michigan and never had a problem with cold start.  I've put about 14,000 miles on the vehicle since the swap with no problems.

How does it run?  Fantastic!  Gets about 23 mpg.  Just added an intercooler about a week ago.  Haven't burned a full tank of fuel yet to check the mpg, but it seems like I might have picked up 2-3 mpg.

Yea, it does vibrate, but if you want a smooth ride buy a Caddy.  Every where I go people stop and ask questions.  The engine sound is identical to 1989-93 Dodge truck equipped with a Cummins.

The vehicle has more torque than I know what to do with.  I can idle in fifth gear (37 mph) and it just goes.  Step on the gas and it pulls away, can't lug the engine.

As for the weight of the engine, it is no big deal.  It weighs about 200 pounds more than a 4.0L six that was available.  The front suspension won't know the difference.  The 4BT weight is all behind the front axle which helps distribute the weight more evenly.  The vehicle dose not feel nose heavy.  

Edward A. Sanchez Edward A. Sanchez
Administrator | Posts: 2112 | Joined: 07/06
Posted: 07/18/08
10:42 AM

Arizona, that's some great info! I know there are several guys on here that have done or are interested in doing some diesel Jeep swaps, and they're always asking very detailed technical questions in terms of the components needed to do the swap successfully. Thanks for the post!  Smile  

ArizonaPerfect ArizonaPerfect
New User | Posts: 20 | Joined: 07/08
Posted: 07/28/08
05:17 AM

Just a quick update on my 4BT equipped Wrangler.  Burned two tanks of fuel and the intercooler has increased the fuel economy to just over 24 mpg (approximately 1.2 mpg gain).  

On the first tank I went 340 miles on 14.1 gallons (24.1 mpg).  On the second tank I went 225 miles on 9.1 gallons (24.7 mpg).  So the vehicle seem relatively consistant, pulling 24 - 25 mpg.

My latest change over the weekend is to swap the 3.55 gears in the rear axle with 2.94 gears.  The 2.94's brought the rpm's down about 400 rpms at all speeds.  The vehicle now turns 1800 rpm's at 70 mph.

The 4BT has no problem spinning the new gears.  The driveability of the vehicle is pretty much unchanged.  The torque output of this engine is amazing.  Idling in 5th gear the vehicle speed is about 40 mph and doesn't lug at all.

If the new gear ratio increases the fuel economy, I'll probably have to swap out the 8 3/4 Mopar rear axle for a Ford 9-inch and up the ratio to a 3.07.  Then install 3.07's in the front axle.  

I would rather keep the 8 3/4 with the 2.94's but, unfortunately, no one I know of makes a 2.94 gear set for a Dana 30 high pinion front axle.

Switching to a 9-inch Ford front axle would give me the 2.94 ratio I need, but there is not enough clearance to the oil pan of the 4BT.  I would have to increase my lift kit from a four inch lift to a six inch lift.  Something I don't want to do.

I'll report the mpg results (due to the gear change) after I burn a couple of tanks of fuel.  

Blizzard460 Blizzard460
User | Posts: 103 | Joined: 04/08
Posted: 07/28/08
08:46 AM

thanks for that info, how much do you think that swap costs total, about how many hours do you have in it and where did you get the 4bt from?  
96 F-250 460 V8, Extended Cab, Short Bed K&N Filter, Crane Cam, Ford Racing aluminum heads, 4.56 diff, Eaton lockers, Hooker Headers and Flowmaster Super 40s, true dual

2004 F-250 6.0 Powerstroke, 4 Door, Short Bed, Lariat, 5 inch MBRP dual outlet exhaust, Banks Big Hoss Bundle Kit

1993 Jeep Wrangler, 2.5 I-4, 30 in. BFG All Terrains, hoping to do a 4bt swap someday...

Proud member of the Blowin' Smoke Gang!

Edward A. Sanchez Edward A. Sanchez
Administrator | Posts: 2112 | Joined: 07/06
Posted: 07/28/08
10:46 AM

There's not that much of a ratio difference between 2.94 and 3.07, so you should be getting about the same fuel economy one way or the other. Sounds like it's running good!  Smile  

ArizonaPerfect ArizonaPerfect
New User | Posts: 20 | Joined: 07/08
Posted: 07/28/08
11:31 AM

I paid $3,000 for the engine on eBay.  Fortunately, it was a brand new (still on the crate) 23 year old engine.  

I would say approximately another $3,000 for a radiator, trans adapters, motor mounts hose, belts, exhaust manifold, electronics for the cold start aids, clutch, and exhaust.  Depending on how resourseful you are the price could be higher or lower.  I bought a lot of the stuff from eBay.

As for how long it took to build, it took me about 50 hours total to go from a running 2.5 gas to a running 3.9 diesel.  Again, the time to build would very greatly depending on your skill level, facilities resources and parts availability.  

ArizonaPerfect ArizonaPerfect
New User | Posts: 20 | Joined: 07/08
Posted: 08/07/08
04:51 AM

Did my first MPG check on the 4BT Cummins Wrangler  since I replaced the 3.55 gear set with 2.94 gears.  MPG went up about 2 miles per gallon.  It got 26.3 MPG (271 miles on 10.3 gallons) driving around town.  Haven't put it out on the highway yet to see where the MPG goes.

Since the gear change helped fuel economy, I picked up a couple of old 9 inch Ford axles and am in the process of installing the axle in the back with 3.07 gears.  This way I can keep the original Dana 30 front axle and just install 3.07's to match the rear axle.  That should eliminate drivetrain wind-up problems and keep everything in sync.  

landonrydell landonrydell
New User | Posts: 7 | Joined: 08/08
Posted: 08/13/08
09:12 PM

sounds like you have it all figured out.I have played with the 4bt for a few years now. and have been very pleased with them. I have one in a 90 dakota and one in a 01 durango. both have dodge automaticoverdrives in them. I get 25 mpg in dakota and 20-25 in durango it does a lot of idleing to keep them kids cool. both have a/c and the durango is intercooled. durango 3.55 gear dakota not sure never checked gear maybe 3.55 or 3.80 gear. it has a 8.25in dana  

Edward A. Sanchez Edward A. Sanchez
Administrator | Posts: 2112 | Joined: 07/06
Posted: 08/14/08
01:56 PM

Icon QuoteArizonaPerfect:
Did my first MPG check on the 4BT Cummins Wrangler  since I replaced the 3.55 gear set with 2.94 gears.  MPG went up about 2 miles per gallon.  It got 26.3 MPG (271 miles on 10.3 gallons) driving around town.  Haven't put it out on the highway yet to see where the MPG goes.

Since the gear change helped fuel economy, I picked up a couple of old 9 inch Ford axles and am in the process of installing the axle in the back with 3.07 gears.  This way I can keep the original Dana 30 front axle and just install 3.07's to match the rear axle.  That should eliminate drivetrain wind-up problems and keep everything in sync.


That's great mileage for a Jeep! Wow, I'm finding out how popular the 4BT swaps are!  

landonrydell landonrydell
New User | Posts: 7 | Joined: 08/08
Posted: 08/14/08
04:20 PM

i have had the dakota going for almost a year. i noticed one thing about fuel milage. the thing gets about the same in town or blazing down the highway at 65-75 mph. not real sure why it does this. but if i were to putt around at about 50-60 mph i think it would get a little better econemy than what i get. but it has all the power a little truck could dream of. the engine that is in my durango was once in a 3/4 ton chevy 4 door long bed  with a turbo 400,3.07 gear and if i drove it right it would get 23-25 mpg out of it. the second i hooked a trailer on it or got in a hurry or on the interstate the milage dropped to under 20mpg quick so this is why it its in a durango now.  

rrbgtt rrbgtt
New User | Posts: 14 | Joined: 08/08
Posted: 08/19/08
07:36 PM

I would love to see some photos of your conversion.  My son and I just finished installing a 4bt in his YJ.  We went a little different route.  Instead of looking for economy, we went for power with ours.  It has the pump turned all the way up, a slightly larger turbo, intercooler, 3200rpm spring, and we advanced the timing.  We have a Dana 60 front and 14 bolt rear with 4.88 gears, a Th400 manual valve body transmission and NP205 Transfer case.  Even with things turned up and the low gears, we can still be 20mpg on the highway around 58mph.  The only problem we are having is keeping all the bolts tight.  It seems to vibrate everything loose.  

ArizonaPerfect ArizonaPerfect
New User | Posts: 20 | Joined: 07/08
Posted: 08/26/08
09:24 AM

Wow! 4.88 gears......top speed must be around 58 mph.  That is great for off roading, but probably not the best for a daily driven vehicle.  Sounds like you have the ultimate in indestructable drivetrains.  A 4BT, Turbo 400 trans, Dana 60 front axle and a 14 bolt rear......yup, we won't be seeing you broke down on the trails.

My drivetrain package is not nearly as strong as yours.  4BT, AX15, Dana 30 front axle and a Ford 9 inch rear axle.  Again I think we had different goals in mind when we built our vehicles.  That is the great thing about this sport.......you can have the same vehicle, yet be completely different and original.

Right now there is no rear axle in my Jeep.  I'm in the process of replacing the 8 3/4 Mopar axle with a 9 inch Ford.  Once done I'll take some new pictures of the vehicle and attach them.

Oh, on the second tank of fuel, since the gear ratio change, the economy was 26.79 mpg (485 miles on 18.1 gallons).  So the vehicle seems to be very consistant.  

My goal is to get the vehicle to 30 mpg while retaining as much of its off-road capabilities as possible.  Are there any tricks to the injection pump or injectors that any one knows of that might help me get to my goal?  Any advise or experiences would be appreciated.  

Edward A. Sanchez Edward A. Sanchez
Administrator | Posts: 2112 | Joined: 07/06
Posted: 08/26/08
05:11 PM

9-inch is nothing to sneeze at. Short of a Rockwell, they're pretty stout. Shoot, I've even seen a Rockwell go out. I guess nothing's indestructible if you punish it enough.  

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