D60 or....?

[RedneckTexan]

I want to put a 6bt Cummins in a Hi-boy this summer, but I was wondering is the D60 in the rear strong enough for a hi horse power Diesel that size? should I up-grade to a D70-D80? Maybe a Sterling 10.25? any thoughts?

[averagef250]

Depends on weight, traction and clutch/converter.

Basically, no, even a built to the hilt 40 spline 60 with a spool, billet caps and cap studs won't take it. It all boils down to whether your engine actually makes big power or not, how hard you run it. The carrier bearings and pinion diameter in a 60 are not big enough for the torque.

I've personally seen a dana 70 from a P-pumped dodge with the ring gear bolts sheared clean off. The 70 will hold up for awhile, but the 80 seams to hold up pretty well. The downside is you'll lose economy with the 80 though.

The sterlings are pretty much par with a 70, they'll break with a lot of abuse, but hold up well.

1410 U-joints are also a requirement.

[RedneckTexan]

So do you think that a Dana 70 DRW will hold up behind a bone-stock 6bt cummins

how about a 4bt cummins? will a Dana 60-70 hold up better behind a 4bt?

[averagef250]

There are lots of different "stock" 6BT engines. A stock 16 spline 60 rear would last awhile behind a stock 160 HP rotary 12 valve that didn't tow much. A dana 70 would have a rough go behind a stock dodge 215 HP motor. The HP ratings are one thing, what they actually are is another.

A "high HP" 6BT means 800+ lb/ft to me.

John, The beauty of these engines is that they don't have to be brute power all the time. With some very basic tools and no parts (maybe a fuel plate) you can go from 160HP to 300HP. Increasing the HP in a diesel just means you're increasing the efficiency of the engine. If you have a nasty turbodiesel and you turn the fuel back down you have a stock engine again.

Even at high power levels, the gas pedal still works just like stock, except for the last part. When you increase fuel delivery on a mechanical injection diesel you're just increasing it at the top end of pedal travel. Pull the top off a rotary cummins injection pump if you get the chance. They are rediculously simple inside and you can see exactly how the thing works and what the throttle input really does for the IP.

[RedneckTexan]

That's sounds pretty cool Dustin, I think I'll pull apart the shop truck where I work and take a look at the rotary injection pump (It's a 6.7L cummins)

[averagef250]

The 6.7 is not a mechanical engine. It doesn't even have an injection pump.

[James72]

That must be the common rail then?
If so, if you put a wrench on any external high pressure lines you have to replace them!

[Dragon]

I have seen Dana 60s handle A/Altered in the quarter mile and D70s in rails back in the 60s and 70s. Also ford 9 inch rear ends made their way into several rails in the NHRA. So they all hold more power than the diesel. What mattered most was having the rear end bearing surfaces and centerlines true to specs. Misalignment has blown more rear ends then I can count.

[averagef250]

They will hold far more horsepower than what most turbodiesels could dish out.

They will not handle the torque. Torque and horsepower are very different things, especially in a heavy truck.

A Heavily fueled pickup turbodiesel can easily put 1000 ft/lbs to the pinion in direct. That's 4000+ lb/ft of continuous dynamic torque to the pinion in first gear. Not even going to think about the shock load from a full throttle 1-2 shift.

It's not just the dynamic torque potential of the engine. A 5.9 cummins complete rotating assembly weighs about 350 pounds including flywheel/clutch or converter. Most drag racers are defueling their 12 valves around 5000 RPM. The instantaneous torque potential of an engine with that kind of rotating mass at that RPM is pretty insane.

[68Mercury250Ranger]

DRW 70 from a cab/chassis truck will bolt into your highboy project.
a 60 is not enough for a 5.9 even stock. If you are going to work the truck, towing or pulling, a 70 might hold up but getting an 80 from a Dodge pickup would probably be your best bet. Easy to weld spring pads and shock mounts on.

A 60 behind a 4bt might be alright, but the coarse spline ones are not as strong.
Averagef250 is definitely the experienced one with the 4bt.

[averagef250]

I still have the original 16 spline 60 under my 4BT 71. It's still nice and tight, but we'll see how long that lasts. I'll probably swap in a sterling if I break this axle.

The 4BT is a little different. It doesn't have the same instantaneous torque potential as a 5.9. The 3.9 builds all it's power with boost. Off idle power is good, but there is a very noticeable difference between 3.9 non-boosting torque and 5.9 non-boosting torque. The 3.9 also lacks about 80 pounds of rotating mass compared to the 5.9. Basically, a clutch dump or power shift with a 3.9 is a lot less potent than one with a 5.9.

I've found with my 4BT that the 11" clutch is the limiting factor. Under the hardest use I've put the truck through (16,000 GVW) so far, The engine would boost very hard in 2nd and 3rd and was managing to blow through the clutch under 2000 RPM. I also found with the same very hard loading the engine will pull all the way to 3500 before de-fueling. I liked it. The Cummins 4 sounds like an old Jimmy wound that tight.

[RedneckTexan]

Sounds like the 4bt is the way to go. I'm still searching for a hi-boy, but I (think) I've found a D80 SRW, Which leads me to my next question, would a 197? international bread van come with D80

And also, would a stock D80 handle the torque of a 6bt? I'm still probably going with the 4bt, but I was just wondering.