Best D-Unit Engine Size (for Class 5)

[guest]

In spec-ing a new Class 5 D-unit, I am interested in your thoughts on optimum HP size for HP.

Tradeoffs between HP, weight, and MPG have my head spinning.

Looking at a Detroit-D Seires 50 @ 250-275 HP, or a CAT C-10 or 3126B (275 HP).

 

[guest]

Both good choices or the Cummings ISB 260 HP as it has a 2 year
unlimited warranty regardless of mileage. You do run a lot of miles if you are a team; like 300,000 in 2 years. Watch out for rear end ratio. You can't get good mileage if you are "wound tight"
a 65 MPH. You want to tack about 1800 RPM at 70 MPH and you can
get great mileage. Some of our Cummings engines are getting between 12 and 13 MPH at about 60 to 65 MPH. Ed

 

[guest]

I owen 3 of the 3126 cats and im not impressed at all the wireing on the injector-(plugs) go bad often and if you put it in the shop to fix it they replace plug and the injector and the injector is about $250.00 each plus labor and it not usually anything wrong with the injector I would recommend the ISC cummins 250,300 hp oil changes ever 15,000 miles the cat is ever 8,000 miles and the ISC is a wet sleeve engine it can be rebuilt I hope that helps MERRY CHRISMAS AND GOD BLESS

 

[guest]

Thanks!

I, too, have heard axel ratio spec-ing is the KEY to good fuel economy (#2 behind driving style). Many are recommending a 3.70 ratio. Given the average freight weight for a D Unit (between 4,000 and 5,000 lbs), this ratio needs to be driven by at least a 250 HP engine -- this is what I'm being told, anyway.

Appreciate your thoughts on both minimum power (250 HP as a min.) and best ratio (3.70 -- runs in the engine "sweet spot" at 65 MPH).

THANKS!

 

[guest]

Thanks!

I have heard many CAT owners say that's the last one they will buy! Appreciate your honesty and experiance.

Mr. M

 

[guest]

take in account how many gears you have. 5,6,7,9,10. I have a ISC 330HP, 7 speed, 3:58 rears. it works nice 75mph in the mid of range
and plenty of power left. getting 14.5 mpg with fuel the way it is you need something working for you.

 

[guest]

Okay, Iceman, How do you get that kind of mileage with that baby? I've got an M-11 330/370 (pretty much same as yours) with a 9 speed and she'll give me 10.1 on a VERY good day, average 8.6. Not sure of my ratios, but she runs 1400 rpm @ 65 mph.

 

[guest]

Ouch! Look at the Cummins ICB