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Choosing the correct engine, trans, and rears for mpg

I'm getting ready to order a new truck for my flatbed operation. A mid roof freightliner cascadia is my truck of choice with a Detroit engine. I need help choosing the correct engine horsepower, transmission and rearend to achieve maximum fuel economy running 60 mph. I usually heavier loads also. Thanks

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Running heavy most the time I would go with the DD15, I'm not sure what your options are for horsepower, somewhere around 500 would work great.

If you can get a direct drive 13 speed transmission, thats what you want. That is a new option in a 13 speed from what I have heard. If you get the direct, then you will want a 2.64 rear end ratio.

If you can't get the 13 direct, then you need to choice if you want a 10 speed direct with 2.64's or choose a 13 or 18 overdrive with 3.55's. Or get an 18 speed with 2.64's and run in 16 gear, which is your direct gear.

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I agree with everything Matt said.

The nice thing about the DD15 is they have a nice wide power band and can ull good all through the power band. You really can't go wrong.

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The optimal choice in the dd15 is 515 hp, get the 13 or 18 speed. The tall gear ratios only save fuel if you have the horsepower and drive it correctly.

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Or, you could just do an 18 speed, with 2.47, 2.65, 2.79, or 2.90 rears, and run in direct (16th) at 60 mph for max mpg like Matt said. In 16th, with 2.79 and low pro 22.5's, at 60 mph you would be turning just higher than 1400. For something like the DD15, I would probably go with 2.65 or 2.64 (depending on axle make). With 2.65 and low pro in direct, the rpm would be roughly 1375. I just ordered a glider with 18 speed and 2.79 rears. Just match up the rear ratio to the ideal operating range of whatever engine you choose while running in direct on the tranny. An 18 will give you another gear up if you feel the need to move along quicker, plus you will have all the splits into the basement for max pulling. And the 18 has deeper reduction and better spreads than something like a 13, so running a tall ratio will not kill you. Make sure and spec high torque clutch and drive train. If the engine has, say, an 1850 torque rating, spec a 2050 driveline.

I don't agree with Jess on this one. Actually, running in overdrive steals hp from the rear axle. Running in direct, all the available hp and torque is making it to the rear wheels. You actually need MORE hp and torque to run in overdrive than in direct with the same load, terrain, etc. That will cost you more fuel. Jess is right though.... you have to drive it correctly. But that is true for any engine, tranny, rear end combination.

I am not sure why something like an 18 running in 16th (direct) with tall rears causes so many people's brains to lock up. It isn't that big of a deal. Going back to pickups and autos, the manufacturers recommend towing in direct drive only. It is the same principle applied to big trucks when you do something like an 18 tied to a tall rear end.

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Need help deciding. Is the DD15 455 hp with a 10 speed direct, and 2.64 gear ratio going to get the job done for me. will it pull the hills and mts. with relative ease? I'm not looking to scream up them just don't want it slowing down as soon as it sees the hill!!!

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I never have that problem with any hills with 2.64 behind my Series 60. It all depends on the transmission ratios and what RPM the engine is at. If the engine is already at the bottom of the power curve when you hit the hill, it is going to choke. I use an 18, but run primarily in 16th (direct), and I can walk hills just fine with 46,000 in the box. I do it regularly with bulk ag products, rolled steel, etc.

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Hi I am bringing my 1995 freightliner to the road I got 500 HP12.7 Detroit 24.5 tire size and 3.90 ratio with no transmission but got buy transmission what transmission is good for best fuel economy 18 or 13 over drive there RTOL18918 B &A also 209018 and 18913A and 16913A

I can't find direct transmission and I don't liked. I always pulling flatbed 45000 lbs in flat road

I like lower RPM to have quite cap I prefer not go more 1300 RPM in high gear at 66 Mph

Please let me know with your best acknowledge and experience

Thanks

Thanks

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good morning

we just started with trucks with DD15 engines

we have eaton 13 speed transmissions, and our top speed is 72 miles

we use LP 22.5 tires

can you advise is there is a tool wich will allow us to move rear end ratios, to look for the best possible MPGĀ“s?

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