4bt vs 6bt cummins swap

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93 cruiser ben_jamin

93 cruiser ben_jamin

10 Year 15 Year
Joined
Sep 3, 2008
Threads
11
Messages
35
Location
colorado
Im currently selling my land cruiser to get one with less miles on it, but in a recent magazine article in peterson 4wheel drive showed a 94 cruiser with a 6bt cummins and wanted to know if the swap is better than a rebuilt or engine with lesser miles. I live in colorado and proffitt's cruisers do a 4bt with a intercooler. Obviously the 6bt has more power capability but can the frame really handle the weight and torque? Everything I have found says that a four inch lift is required just to clear the oil pan. Also seeing how he 6bt is deeper than the 4bt adding a intercooler looked almost impossible.
 
My vote is for the 6BT. Your 80 came with an inline 6 and would like to stay that way:). It is a smoother powerhouse. Intercooler placement will require ingenuity but IMHO is worth it. Frame should handle the 6Bt in stock form. Recommended: 94-97 12 valve p7100 pump KDP tabbed.
 
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I have long pondered the Cummins Question. Obviously it has been done both ways.

This is what I have found:
4BT:
Short, could fit almost fit in FJ80, still too tall.
750-800 lbs.
About 50 lbs heavier than TLC I6 (per Proffit)
Intercooler can fit.
Hard to find, expensive
Stock HP low (low rpm power band) but much more difficult to modify for higher output AND decent ecomony??

6BT
LONG!
Heavy!! 1150-1200 lbs
Only seen non intercooled models swapped into FJ80s (intercooled may have been done too, just have not seen them)
Easy to find.
Plenty (too much?) torque stock, non IC models still lowish on HP.
Easy to get power, but see above.

If you have not driven a Cummins Diesel, be aware that the limited powerband (basically 1400-2800 rpm) takes some getting used to, especially with a manual.

(I just bought my first Cummins Ram a few weeks ago, an 05 with a 6 spd manual. Definately takes some getting used to!)

Something to be very aware of with swap is your final drive ratio. My 05 Cummins has an OD ratio of .79 and 3.73 gears with 31" tires. My motor is turning WAY too fast on the interstate like around 2500 rpm when it feels like it should be turning 1500 rpm. Above 50 mph, my MPG drops quickly, it feels like I am using more fuel to spin the motor faster than to actually move the truck. (Yes, I realize aerodynamic drag is a V^2 loss).

FJ80 axles have 4.1 ratios, if you used a T700/4L60 which has the tallest overdrive (.7) of any non 6 spd auto tranny for trucks, you would be spinning 2200 rpm with 33" tires. You could live with that, but would not realize full MPG potential of a Cummins conversion.

:cheers:

Jule
 
I havent driven a 4bt, but i do own and drive a 6bt. The swap was done by the PO, and i have been doing a lot of work fixing the bugs. There is still room in the engine compartment with electric fans and stock rad, I bet if I really wanted I could stick an intercooler in front of the rad, mine is a non-IC model though and I havent had time to ponder this mod yet. I will say the following things though...

The cruiser is heavy, throw on an ARB and 8274, there's more than a few pounds on top of the heavy motor, actually I am contemplating one ton axles, not that I have broken anything, but thats just a matter of time. Just something to think about.

The 4BT would be a better match weight wise, although, from what I understand of there is a fair amount of 4bt's that go up for sale with dynamating and sound deadening installed through out, I think the 4 cylinder diesel by nature(and harmonics) is a loud motor.

So definately pros and cons to both i guess...
 
Jule said:
Just a newer version of the 5.9 6bt (i.e. electronics)

Cummins B Series engine - Wikipedia, the free encyclopedia
Click to expand...

biggest differences in 6bt and ISB are (1) computer controlled and (2) 24 valve, not 12 valve.

The 24v ISB is a beast. I have one in my 37 foot motorcoach. It tips the scales at 26,000 pounds, and with my truck in tow, my GVWR is right at 32,000 fully loaded. The ISB pulls me through the mountains at 65 mph and 9.5 mpg.

cody c said:
my axles are so scared of that amount of torque i think a little fluid just dripped out...


(of the axles I mean)
Click to expand...

now that is funny.
 
A 4bt can put out way more power than the stock 80 axles can handle. You just have to know what you're doing. So I wouldn't be worried about power potential here. A built 4bt can destroy alot of driveline parts. 6bt is a whole other level of swap where serious consideration must go into axle swap and other modifications. You heard it first hand on here already. These are the reasons why there are more sawps involving the 4bt instead of 6bt.
 
TheBadfish said:
A 4bt can put out way more power than the stock 80 axles can handle. You just have to know what you're doing. So I wouldn't be worried about power potential here. A built 4bt can destroy alot of driveline parts. 6bt is a whole other level of swap where serious consideration must go into axle swap and other modifications. You heard it first hand on here already. These are the reasons why there are more sawps involving the 4bt instead of 6bt.
Click to expand...

There are a few other variables there as well...

Open diffs or locked, expedition, grocery duty or crawler, 31's or 39's etc. etc.

I do agree on the comment about other mods, but like many of us, we dont know when to stop anyways...

I havent had any probs with the axles myself, but alot of bugs everywhere else, though, it will probally just be a matter of time till I have upgraded the axles in one way or another.
:cheers:
 
I was referring to the author of the thread when he said the "power potential is greater with the 6bt". They are both great engines, and almost the same engine minus 2 cylinders. But make no mistake about it, there are 800hp 4bt's out there. I was just saying that the 4bt can produce more power than you even would want in the cruiser. So power shouldn't be a criteria for this swap. They are both very capable engines and have dealt with them both.

I still believe that the weight of the 6bt over stock axle is excessive. This is just one reason that I would go 4bt.
 
TheBadfish said:
I was referring to the author of the thread when he said the "power potential is greater with the 6bt". They are both great engines, and almost the same engine minus 2 cylinders. But make no mistake about it, there are 800hp 4bt's out there. I was just saying that the 4bt can produce more power than you even would want in the cruiser. So power shouldn't be a criteria for this swap. They are both very capable engines and have dealt with them both.

I still believe that the weight of the 6bt over stock axle is excessive. This is just one reason that I would go 4bt.
Click to expand...

I hear ya, if your ever in calgary give me a shout and we can take the 80 for a burn and see how it feels, I wouldnt mind the oppurtunity to drive a 4BT'd 80 for a better informed perspective as well.
 
I'm pretty sure both would be a beast to tow .. but I honestly if you are not thinking in big loads, to tow and all that you want it's powa work on your stock engine ..

If you want a TDI .. 1HD-T or FT version ..
 
I thought about putting my 6BT into an 80, but it would be a bad match in my opinion. It's a towing motor. The 80 is too short to tow to the 6BT's potential.

I'm not too sure the viscous coupler would handle the torque very well either.
 
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