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Discussion Starter #1
This seems like as good a place as any to introduce myself.

I have an early 77 F250 4x4 Highboy. It currently has an NV4500 that I have adapted to fit the 400 V8. The truck has served me well for 10 years.

As the engine is getting tired, I am exploring the possibilities of a 6bt or 4bt swap. I do tow with it and would love to get better mpg than the 8-9mpg I'm getting now.

I plan to do a lot of searching and reading and will hopefully not post too many stupid questions.

Thanks
 

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Welcome aboard!
Did the 4BT/ZF5 in mine for the same reasons and it was the best mod done ti the truck in the 25+ years I've owned it i get 18/20 mpg in real world situations and up to 12,000# CGVW it will run with flow of traffic have run it north of 16,000 CGVW and still was not a slug would run faster that it should probably go at that weight.
 

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benefits of the 6bt--easier and cheaper to find--gets the same mileage as the 4bt with less vibration/noise....if i had the 4bt i would run it in a smaller vehicle like a scout or jeep and wouldnt be upset if girlfriend/wife/mom didnt want to ride around with me because of the noise and vibration....
 

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Good points but for me the length/weight of the 6BT in the older Fords tipped the balance in favor of the 4BT.........but I'm at or just over what the 4BT is comfortable doing and I'm sure I will need to overhaul it sooner than if in a smaller/lighter rig.The 4BT spends nearly all of it's time at interstate speeds near max boost/power........there will be many trade offs/compromises to decide on before you are through with this undertaking so do your research it will pay you back tenfold in the long run
.
 

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Discussion Starter #5
I appreciate all the prompt responses.

eggman,
Your signature line says that you have the D44 front axle. Is the weight of the 4bt a concern of is that only the case when you get into the 6bt?
 

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The 4BT is 150/200# heavier than the 390 it replaced add another 400+ for the 6 I'm running a d44 from a '77 currently and so far so good.....but a D60 is on the short list and in all honestly is mandatory I've been looking for a '78/'79 Ford one but have yet to find one that wasn't priced worth it's weight in silver! looking to narrow one for it now.
I wouldn't even consider a 44 under a 6BT just asking for trouble IMO,the 4BT/ZF5 was a factory drive train in Brazilian F series's but the rest of the world run smaller displacement engines than we see here. My 4BT is around 200+HP so power wise its comparable to a 1st Gen 6BT but as stated earlier it's working hard nearly all the time we made a round trip to central CA. from the Flagstaff area over the holidays with a road of boulders and the 4BT spent hours on end making 25+psi boost and 1,150EGT's so in all honesty it's seeing a hell of a duty cycle and does it without complaint but that does come at a cost but an overhaul is not overly complicated or costly and I accept the trade off. I got my 4BT in a running bread truck with 236,000 miles and have since put another 30,000 or so miles on it and it's still running strong and happy so if in 75,000/100,000 miles I need to do the overhaul I won't complain but a 6BT would have been much easier to find and cheaper to do,but with the 4 fitment was easier the 4BT,radiator,inter cooler and fan all fit without firewall mods and a rear sump pan cleared the front axle with the crank shaft center line still sitting at least as low as the factory engine.



 

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Discussion Starter #7
I was lucky enough to find a reasonably priced front D60 from a 79 F350 4x4 a few years ago and snatched it up quick. So I have weight capacity handled.

I'm really looking for the best combination of: cost of install, ease of install and most power/torque for my money.



on a separate note, how do I add a signature to my profile so I can add all these details to each post?

Thanks
 

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At the top of page the my profile link
 

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settings not profils....sorry.
 

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Discussion Starter #11
How much more difficult of an install is the 6bt versus the 4bt?

It seems like I could buy a running 89-98 Ram with a 5 speed and have basically everything I need for the swap. Is this true?
 

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I'm basing this on looking at the 4 in mine but it would seem that with the 6 either the front cross member or the firewall is gonna be in the way and I "think" if the cross member in the rear could give you problems with the bell housing where mine is sitting the bell housing is very close to the cross member and where the tunnel meets the firewall needed a bit of work and my Crewcab is from a F-600 to the access hole is much larger than on the pickup cabs look at my photobucket and you will get a better idea link is in my sig. I tried to keep engine as far back and low as I could for better overall balance so there are other solutions to this than the route I took ;)
 

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Steve, how much further will your motor go back? Looks from the second pic you could go back another 3" possibly with the recessed firewall. The 6bt is 9" longer than the 4bt.
 

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It can't go back any farther due to the cross member/bell housing no more than a fingers width of clearance between them.
 

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there are builds out there with the 6bt into f250----the front crossmember needs to trimmed down--the trsnsmission mount also needs altered---there are good pictures of what needs done...
 

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One thing to be aware of with the 6bt in that era truck is it's a very tight squeeze. It can and has been done. You'd probably need a bigger radiator for the the 6bt but not the 4bt. Which NV4500 do you have. There were 2 GM models and 2 from Dodge. Might require some modifications whichever engine you use.
 

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Discussion Starter #17
One thing to be aware of with the 6bt in that era truck is it's a very tight squeeze. It can and has been done. You'd probably need a bigger radiator for the the 6bt but not the 4bt. Which NV4500 do you have. There were 2 GM models and 2 from Dodge. Might require some modifications whichever engine you use.
I have a GM model from a 98 diesel 2wd. I chose this one because it has the fixed output yolk and allowed me to retain my divorced NP205 via an intermediate shaft.

I was thinking that if I did grab a running Ram I could aim for one with a NV4500 already. That way I would have all the small parts to mate the 6bt up to my trans. Does that make sense?
 

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One other thing to consider is the rear cross member, transmission tunnel and firewall area even with the small block Ford adapter/bell housing is tight so with the larger bell housing from a flywheel/clutch to handle the 6BT's power will be even tighter.......not trying to push the 4BT just wanting you to not get blindsided farther down the line. All of these things can be overcome the sooner you know they are there the easier it will be ;)
 

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I don't see the F250's front dana 44 axle being an issue with the 6bt. I couldn't count all the 70s fords that have had snowplows on them for 20 or 30 plus years without a front axle failure. I cannot recall a 70s F150 with a plow and front axle failure. I built a 78 F250 with a 6bt, sold it and it got a plow with the new owner. I haven't seen the truck but I beleive it still has the dana 44 under it.
 

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Discussion Starter #20
What sort of hp/tq numbers can I expect from the 4bt and still maintain the legendary reliability and longevity of these engines?

Can it be made close to a stock 6bt?
 
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