What is the Best engine Detroit dd 15 or cummins isx?

Answer 1

There are three reasons to buy a Cummins ISX over a Detroit DD15: if you need 600 horsepower and you can't bring yourself to buy a DD16, if you like running the engine at 1500rpm like we all learned to do in CDL school, or if you don't like Freightliners.

The main reason to buy a DD15 is it's more fuel efficient than an ISX--if you can keep the RPM down. It wants to run somewhere around 1250-1300rpm, and loses a lot of power at 1500. So...when you buy the truck, you tell the sales rep what you're hauling and on what kind of terrain you're running on, and let the dealer help you get the transmission and rear end gears you need.

If I was going to buy a truck right now, which I'm not--they're really expensive and I haven't won the lottery yet--I would get a Freightliner Cascadia with 600-hp Detroit DD16, moose-guard bumper, 18-speed autoshift, super single drive tires and 3.55 rear end. 18-speed will save you a lot of fuel if you know exactly how to shift it but will clean your bank account out if you don't; the autoshift system solves that problem. 600hp is for hauling heavy loads up big hills; if you're sitting on the side of a mountain in Pennsylvania or Idaho with a load of beer in the back, the only thing that's going to get you up efficiently is a huge amount of horsepower. Super singles are better for fuel mileage, and the Cascadia has a very nice sleeper.

Adding to the above, the Cummins ISX motors have gotten a lot better since the first generation of them came about. However, I'm still of the opinion that the pre-ACERT N14 motors were much better (and I feel the same way about the old 12.7 litre 60 Series Detroits over the 12.8 litre MBE4000 and DD13, as well as the 14.0 60 Series - but you kinda get into the apples vs. Oranges debate comparing the 12.7 to the current DD15).

If I were to buy a truck right now (and, as above, I'm not intending to), it would probably be a Kenworth T800 with a wet line, 50k rears, a 23k front, and a double frame. For that application, your only current options are the ISX15 or the 12.8 litre PACCAR MX motor. The ISX has a wider powerband than the DD15, which would be beneficial for the applications I'd use it for. I'd run an 18 torque 18 speed Eaton Fuller (while it can be a bit excessive for a typical road tractor, the real value of the 18 speed is in off-road and heavy haul applications), and either 4.11s with an overdrive transmission, or 4.33s with an 18 double over. It's a niche which the (no longer available) Caterpillar and Cummins motors are much better suited for than the Detroit.

One thing you have to keep in mind, as well, is that, the higher displacement the motor, the higher the tare weight of your vehicle. Sure, it's nice to have a DD16 Detroit, C16 Cat, or D16 Volvo (at least, so long as someone else pays the maintenance bills for the Volvo), but they're much heavier in comparison to the motors in the 13 litre range.

By the way, horsepower is less important than what it's made out to be. The Cummins 6.7 found in current Dodge pickups can crank out over 500 horsepower, but it's in no way comparable to, say, an ISX motor cranking out 500 horsepower. The displacement, powerbands, and torque ratings are much more relevant here.