To Cummins 6bt or not to Cummins 6bt, that is the question (1 Viewer)

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Hi guys,

I'd like your input please. A neighbor of mine has a 1993 80-series (unlocked) that has a Cummins 6bt stuffed into it. He's selling it, and I've been chatting with him about buying it. Here's what I know:

  • He said he used one of the kits from Duiser to do it.
  • No factory lockers
  • 1994 5.9 Dodge Cummins, everything else is stock.
  • He did the Killer Dowel Pin before the engine went in.
  • Engine has about 150K on it
  • Tranny is controlled by a Compushift controller.
  • Looks like a clean install, A/C works, etc.
So, tell me what you think. Am I crazy? Should I consider it? Pros and Cons?

Thanks,

Muddy1
 
Pro: smoother than a 4bt, turbo whistle on the freeway, train-like torque, decent (but not amazing) fuel economy, will run forever

Con: arguably too much weight for a FZJ80 front end, arguably too much torque for a FZJ80 rear end, accessory bracket issues, narrow RPM band, requires significant lift to clear axle (some people want that much lift, others don't)

I am very fond of diesels and seriously considered a 6bt swap but the more I looked into things an aluminum 5.3L vortec is winning out.

Is it TOTALLY problem free? How many miles on the completed swap? Is it a bargain? One being really cheap is about the only way I'd consider a 6bt cruiser, personally. For the way I plan to use my rig (long roadtrips mostly sleeping inside, moderate wheeling, not much towing) one just doesn't make sense. That said, keeping my rig light is pretty high up on the priority list.. for others, not so much.
 
Hi bloc,

Thanks for the quick reply. I am a BIG fan of diesels (owned a mint-condition Chevy Tahoe Diesel (don't hate me!) and it was a great rig. I sold it because I wanted 80-series quality and full lockers).

Great questions. Here are my answers:

  • I want to turn either my 80 or the diesel 80 into an overlanding vehicle.
  • I don't plan to tow, and if I do, it would be something really light, like a small trailer for overlanding.
  • I LOVE diesels - the torque is truly addictive.
  • I am definitely concerned that the rear of the 80 (and the stock tranny) might be a bit light if I stomp on the go pedal too much. :)
  • Overlanding plan: keep it light, lots of highway miles, light to moderate wheeling.

Thanks,

Muddy1
 
He's asking $17-18K for it, but I think I can talk him down. I don't know if he is on Mud. He lives near me.

Thanks,

Muddy1
 
Seems like a good deal. As someone that is in the middle of this swap right now (6BT/NV4500/HF2AV), I know the costs involved and at that price you are getting a good deal.
 
I am a big fan of diesels, having owned 2 diesel cruisers- a BJ70 and a 4BTJ80 (proffits) as well as numerous other makes. Plus I have driven a 6BTJ80 a local has here in ATX. The owner of the 6BT80 bought it with the conversion done (very sloppy and poor conversion) for around 20K IIRC and has put in another 20K to get it right. It does drive nice.

Knowing what I know now, it's not worth the headache. Custom vehicles have custom problems and unless you are ready both mechanically and financially to undertake it, I would pass. I would only do a diesel conversion if it was already in a Toyota, ie, drop a 3B into a FJ60 (BJ60), 1HZ into a FZJ80 (HZJ80), etc. and even then only if the half-cut/truck was side by side.
 
Good price, is it registered? Emissions? What year? You'll see these for sale occasionally in emissions regulated areas because they can't get titled as a diesel.

Did he do the kit or did diesel adapters/ duiser? Makes a difference. I'd actually trust Dustin's work. Probably not someone else.

When was the kit sold? It has changed about 5 times? The version makes a difference....

As a concept I don't like the diesel mated to the auto. Super simple, reliable engine mated to an auto with an overly complicated shift kit. Makes no sense.
 
Thanks for the thoughtful responses, guys. I agree I would greatly prefer an NV4500 mated to the Cummins.

What makes the shift kit overly complicated?

Sincerely,

Muddy1
 
to get the MPG out of it you need gears unless your happy driving 60mph add ARB's while your at it. i'm running 3.55 gears 4BT very happy. my buddy has the same set up but 6bt both with stock toyota trans. i'm just reaching 10,000 miles on my swap starting with a 230k trans no rebuild, did a shift kit and increased rail pressure, new pump oring and input seal. no signs of weakness yet. but i'm always worried about the trans being a weak link. price doesn't sound bad assuming really clean truck and it drives nice shift as expected.
 
I really liked the 6bt in my sons 1997 Dodge 3/4 ton 4x4. He had tweaked the motor up a bit and it ran really strong. Most of the L/C 6bt conversions I have seen have eliminated the HUGE inter cooler that was on the Dodge. How much power is lost by dropping the I/C?
 
OK, so the problem as I understand it (i.e. Cummins 6BT with stock FZJ80 transmission) is:

Just based on looking at these graphs, and thinking about the driving experience in the stock FZJ80, it would imply the following about the Cummins-equipped 80 with stock auto transmission:

  • Probably OK around town, but geared way too low, probably really pokey getting to high freeway speeds (e.g. 70 MPH)
  • Likely really good at low speeds (on bad roads, crawling over obstacles, towing at low speed)
  • At anything around 70MPH is probably screaming near redline.
I know my 95 Tahoe had great torque (probably around 400 ft-lbs after all my mods), but it was designed at the factory with the drivetrain. I know it shifted really well, and could easily handle 70-80MPH without issues. It got sub-par fuel economy at those speeds, but it had no problems running hours at those speeds.

I'm thinking I'll give my neighbor's rig a good test run, but now I know what I'm likely getting into.

I like the "Custom vehicles have custom problems" comment! Thanks!

Any further comments?

Thanks,

Muddy1
 
WOW. This kid does a GREAT job explaining HP vs. Torque (here I am hijacking my own thread, but it's appropriate for this Cummins discussion).

 
I have done the Diesel Adapters kit in my 95 about a year and a half ago and 22,000 miles or so on it. I have a 2 1/2 OME lift and 315's on it. I can comfortably cruise at 70-75 it will go more for passing and such but I dont stay there too long. At 70 I am about 2100 RPM when I had 285's on 70 was around 2600 RPM. So far no issues with any of the drive train! That price range is about the price I would ask on mine too IF I were to sell.
 
I have done the Diesel Adapters kit in my 95 about a year and a half ago and 22,000 miles or so on it. I have a 2 1/2 OME lift and 315's on it. I can comfortably cruise at 70-75 it will go more for passing and such but I dont stay there too long. At 70 I am about 2100 RPM when I had 285's on 70 was around 2600 RPM. So far no issues with any of the drive train! That price range is about the price I would ask on mine too IF I were to sell.

? i'm confused a 285 to 315 should only drop your RPM by about 150. was your torque converter unlocking due to WOT (full throttle) settings on your trans controller?
 
I have done the Diesel Adapters kit in my 95 about a year and a half ago and 22,000 miles or so on it. I have a 2 1/2 OME lift and 315's on it. I can comfortably cruise at 70-75 it will go more for passing and such but I dont stay there too long. At 70 I am about 2100 RPM when I had 285's on 70 was around 2600 RPM. So far no issues with any of the drive train! That price range is about the price I would ask on mine too IF I were to sell.
I'm cruising at the same, 70-75. It wants to go more but I have to hold it back. Hitting 30lbs of boost is easy in 5th. I've had it up to 90 for a short stretch passing a semi. That best part of the swap is not having to downshift to pass even on hills. Even before engine mods I could hold 60-65 on I70 in the mountains and that's my self imposed speed limit driving it at night with s***ty 80 series low beams.
I would like to hear how the auto does hills. Does it downshift prematurely? The one good thing about the auto is you won't loose boost when it shifts.
 
? i'm confused a 285 to 315 should only drop your RPM by about 150. was your torque converter unlocking due to WOT (full throttle) settings on your trans controller?

I have converter set to pretty much only unlock under 45mph .

I dont know the math but with the 285's at 2100Rpm i was around 60mph and now at 2100rpm about 70mph
 

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