3.9 in a Dakota

[NWhitney]

Anybody ever put a 3. 9L in a Dakota? Any Idea for the cost of the ReCon 3. 9 or a good used one? I am just in the idea stage on this and want to go in with my eyes open.

 

[TGreschuk]

I'm 100% sure it will fit...











in the bed...



Trent

 

[Chipstien]

It can be done with major modifications. It is the height that is the problem. FWIW, there is a 3. 9 in the classifieds right now for 1500.

 

[NWhitney]

Any sizes

I am thinking that a raised hood would get rid of my height problem... but I need to know if anyone has some more specs on size. weight spooks me a little as far as making it tipsy in the corners. I am thinking since a 3. 9 is just a cut down 5. 9 then the bell housing should be the same so a Getrag 5-speed should fit but what about the stock rear end? I am not planning on making lots of power just lost of fuel economy for long trips to work for the person that I am going to build it for. Any input is good and needed. Note: I am not afraid of major work as I have done coverstions before and sometimes want to do things like this just to say it can be done.

 

[Philip]

a 3. 9 V6 measures 16" from crank center line to top of valve covers. With a M1 intake and a holley it comes to around 22".

The cummins 6BT has a measurement of 24 inches from crank centerline to top of valve covers. I didn't even try to measure the below center line mass.



The 3. 9 4BT has the same height measurements.



So that gives you a little info to play with. Do some close measurements of the engine bay on the Dakota. Look at the lowest point you can put the crank harmonic balencer. Then measure upward. You might need a large mail box to cover up the engine.



Is this truck 2wd or $x$?



If you need length measurements on a 3. 9 V6 I can get them. I have a 64 Dart in the garage with a 3. 9 V6 in it.

 

[moparguy]

It's been done and the doer posted a pretty good write-up. I don't recall how long ago, I'm guessing a couple of years.



Start searching the old threads, it should be there.

 

[DavidTD]

Jeff Garmon had the 5. 9 in the 98 Dakota Reg. Cab. Not sure how it would work in the older body style (better or worse) but in the newer bodystyle the 6bt will fit with only minor firewall mods on the factory engine mounts. If the 4bt is the same height, with minor hood mods, that too will close fine. Of course a cool cowl induction hood would be the ticket. It then had a 47re behind it.



It was amazing what did work from the factory such as wiring harness and everything worked. Even some of the sensors were correct. Only thing was a check engine light. (remove check engine light bulb)



There will be fab work. The 6 required custom oil Pan, oil pickup, intake, steering link, various brackets and linkages, and so on.



I love to see some of these running around. They would be economical and if you could get 350 - 400 hp out of a 3. 9, it'd be quick too. Jeff's six was at 465hp running a best of 12. 08 at 113 mph. It needed the hook to do it but I did them back to back in the middle a bunch of 12. 1's.



The front suspension had 2500 coil springs (bolt in) and Koni coil over shocks ( Big $$ ) but they worked holding up the 6bt. The rear suspension was bone stock except for an Auburn LS in the factory 8 1/4 rear end. I still can't believe it, but it took it. Even with the 6, it handled fine. It wasn't a road racer, but it was a blast on the street. (One of these will put somebody in jail oneday) Jeff's handled nearly as well as a factory V8 Dakota IMO. The brakes worked well off the Vacuum pump. Burnouts as long as YOU could stand it or to 90 mph whichever occured first. And the little ol lady in her would get over 30 mpg on the highway.



I think a 4bt is a great idea, and if one guy has done it lets hear about it. I think a sweet little B with about 400 hp and a shot of NOS would make one mean little street ride.

 

[driverswanted]

I've been friends for a good while now with the guy who put the 3. 9 in an older style dakota. His is 2WD. This is obviously easier to fit than the 4WD. He did his for economy reasons, the same as me. Here's a pic of his with no intercooler. He's stock 105 h. p. and made a squared U undercarriage to get his engine mounts low. The sides of the U are welded to the side rails. I'm expecting about 250 hp and greater than 475 lb-ft. from my 4BTA sitting in an '85 shortbed Ram Prospector.

 

[Rotty]

"Driverswanted" what kind of mileage is he getting?

 

[driverswanted]

Just E-mailed him with that question. I can't remember. I know he's not in the sweet spot of the torque curve at highway speeds so he may not be at optimum efficiency. These engines drop in efficiency when you get past the peak torque point.

 

[MMiller]

How is the vibration in the truck? Does it want to shake the truck apart or does that little 4 run pretty smooth? I too have been tossing the idea around with the wifes dakota. Vibration from a 4 cylinder was brought up so I am wondering.



Michael

 

[driverswanted]

The dakota in the photo gets 26 mpg up to 65 mph and 21 @ 70-75. You can see he's well past the peak torque; i. e. volumetric effieciency peak point. He was at my house one day with his Dakota. It did shake sitting in the drive.

He let me drive it down the road but I can't remember any extreme shaking to the point of seeing a blur in the mirrors.

BTW if you search my profile I have two charts listed that show where the major and minor engine disturbances of the 4bt are in the rpm range. It clearly shows why it shakes when it comes up to idle RPM. These charts were developed by an engine mount design software from Lord engine mounts. There is a harmonic balancer that mounts in the front gear train and sits up high in the oil pan. someone reported this was a real smooth running engine. This device should not be confused with the vibration dampener (vd) that mounts on the front of the engine. The vd does not do any serious engine dampening. You can buy engines with the hb but they are hard to find from what I hear. They are reall expensive when you go to Ma Cummins for one. I added the vd to mine but I'm not on the road yet with my project so I can't give an evaluation. Also, I'm not planning on trying it w/o the vd and then switching to it for test purposes. I paid about $125 for the vd and will accept what I get from it. Another post some time ago covered drilling the stock block style engine mounts from the 6bt to work better on the 4bt. I copied this idea on mine and drilled about twelve 1/4" holes horizontally through each rubber mount. I noticed no additional compression when I sat the engine weight back down on the mounts.

BTW. I remembered that the Dakota 2x4 had a custom oil pan to clear what I remember was the steering rack. It was a tunnel cut-out. I wanted to make my project a Dakota or Durango at first put quickly saw how easy it was to do it in an old shortbed Ram. You don't have to wrestle with any clearance issues. You could even use the same cross member mount location and the transmission mount location for your nv4500. I wanted to have my mounts mid engine instead of the normal front location so I made my own base pieces, bolting them to the frame rail just behind the cross member. The only thing I had to do custom was to slice a wedge out of a cast exhaust elbow to turn it down sooner stay clear of the firewall. The 4bt turbo exhaust output is closer to the rear of the engine than the 6bt.

 

[MMiller]

Are these "vd" what someone would also call balancer shafts? I know that some John Deere and Cat engines have balancer shafts that run off the timing gears. If they are out of time and large machines will shake across the floor when started.



Michael

 

[driverswanted]

The balancer shaft is the the unit that bolts up under in the oil pan and has a front drive gear mating to the other gears up front. I should be able to send an image of that. I believe it's in one of my manuals.