I'm seriously thinking about doing the cummins swap in either my 78 Supercab 4x4 or my soon to be aquired 78 crew cab...I want to run an Automatic behind it...and would REALLY like to run a C6...Can the C6 be built to run behind the cummins??? I plan on running 39.5 to 42 inch tires...4:10 gears in the Dana 60's front and rear...I know a lot of you run the Dodge trans or the NV4500....I don't want to run those...at worst case if the C6 is a NO GO...I would prefer to run an Allison trans....Thoughts???

 

I'm currently swapping a '91 6BT Cummins into my '78 Bronco with a C6 and NP205. A C6 is a very strong transmission, it won't have any troubles behind the diesel. Early 6.9/7.3 diesels in the Ford pickups had C6s behind them, in fact. You use the stock Cummins flexplate and starter, and the C6 torque converter, preferably one from a diesel C6, so the stall speed is lower, and buy some adapters.
You can get the adapters at either destroked.com or fordcummins.com.

 

You should do a build up thread in the engine swap forum with pics...would love to see the progress and when finished how it shifts and such....what rear end gears and tire size combo are you running??

 

I'm going to leave the stock 3.50s in the rears for now, with 35" tires. That will let the motor turn 2000 rpm at 55 mph. A little higher rpm than I'd like, but I'll try it out and see how it works. I'd prefer it turn closer to 1600 rpm, so I may be swapping in some 3.00s in the future. With 240 hp and 550 ft/lbs of torque, it won't need much gearing to move out. It'll shift the same way the early 6.9/7.3s did with the C6s, by using a transducer on the injector pump, to regulate vacuum from the vac. pump to the transmission modulator, mimicking a gas engine's vacuum depending on throttle position.

 

Is that accounting for the difference in tire size??? I run 36 inch mud tires on one of my highboy's....I did the figuring and with that size tire and running the 4:10 gears I have...it puts it closer to a 3:50/3:60 ratio.

 

Yes, the 35" tires were accounted for in the calculation.

Here's a couple pics;


This is the motor when it was still in the parts truck, (right now I'm stripping it to epoxy prime and spray it in dark Ford blue)


And this is the Bronco I'm putting it in.

I hope to have it installed and running within a few weeks. Lots to do still.

 

That will be awesome...I HAVE to hear about it after you have it all installed and running and driveable!!! Where did you get your adapter to adapt it to the C6?? What did you have to pay for it??? Is it just the bellhousing adapter?? or??

 

Both fordcummins.com and destroked.com have the adapters to bolt the motor up to a C6. I havent decided yet which to use. Destroked requires their own custom flexplate that bolts up to a standard C6 torque converter, and they also require you to buy a different starter than the stock cummins part. I'm still waiting on the guy's email for a total price, but I know the trans adapter is about $800. If it's too much, I'll have to use the cheaper stuff from fordcummins.com, which doesnt appear to be as nice a setup, but will work. I don't have an unlimited budget, unfortunately.

 

Just my opinion but Dave - you better beef the hell out of that c6 to have it survive behind even a MILD cummins.

You got the cash for 300m input and output shafts as well as all new servos, etc????

 

The C6 came stock in early Ford diesel powered buses and heavy trucks and holds up well even in stock form to big blocks with 500 ft/lbs of torque. The various transmission techs I've spoken to have all said the same thing, a healthy stock C6 will hold up well to a diesel. The shift points and torque converter stall speed should be your only concern in terms of diesel application of a C6

 

and the old 6.0 and 7.3 IDI diesls don't hold a candle to the cummins


You may run one and be fine - I'm not chancin it...

 

Now I'm not talking about a 1000 hp Cummins here, this is an early mechanical unit with mostly stock components.
The Cummins I'm putting in the Bronco is a '91 1st generation, nonintercooled turbo 5.9L, it's rated at 160 hp @2500 rpm and 400 ft/lbs @ 1700 rpm.
The '88 naturally aspirated 7.3L diesels are rated at 180hp @3300 rpm and 345 ft/lbs @1400 rpm. That's fairly close to the cummins, overall.

Also, the early 460s produced twice the hp and 50 ft/lbs more torque than the stock Cummins, and the C6s held up nicely behind those as well.
When I'm done turning up the fuel and adjusting the pump timing, my Cummins should make 250 hp and 500 ft/lbs, well within the reasonable power range of an early 460. If I go crazy and start buying go fast stuff like a big turbo, cranked up injector pump, big injectors, etc, and my Cummins puts down 1000+ ft/lbs of torque, then we'll have a problem. But for now, it's no issue. And I believe the u-joints and stock 31 spline axles will be the weakest links, not the C6.

I've done quite a bit of research on this, gearing up for my project, the C6 will be great for this swap.

 

I know the exact motor you have as I have the same thing sitting here (early 91) right next to my 94 P-pump motor.

With minor pump mods you will hit the upper limit of the c6's capacity. The torque is the killer and with a few pump mods (couple turns o the fuel screw and some timing) on that VP you got and you might have some issues with the tranny.

As for U-joints and axles - with those larger tires you may have an issue soome than you wish. Dave (the orignal poster) is looking at putting this in a F-250 which will have a d44 or 60 front and a 60 rear. The 35 spline axles in those will handle more torque, and with his 205 t-case and axles jumping up to 1350 U-joints isn't a hard task at all - again putting the tranny back to the weak link.

 

Yeah, with the 60 in the back, u-joint upgrade, and np205, the trans will be his weak link. But even so, that C6 will survive better than you think it will! I'm sure tire spin will happen before the trans flings pieces.

p.s. Any idea when your Cummins Ford will be up and running?

 

We'll just have to see how the things hold up. Personally I'd run TH400 before the c6 in the thing, but that's just me.

As for my crew - not soon enough. Although I am back to the point where I can start moving forward again