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I've decided that SCR is looking like the way to go.

What is "SCR"?

Selective Catalytic Reduction. Basically they inject urea into the exhaust to reduce NOx.

Some manufacturers have stated they are going that way, some are not.

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Originally Posted by allan5oh

Selective Catalytic Reduction. Basically they inject urea into the exhaust to reduce NOx.

Some manufacturers have stated they are going that way, some are not.

Blah blah blah kevinite....... :lol: :lol:

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Originally Posted by allan5oh

1) Power is going direct through the transmission. No power is going through the two countershafts, then back to the output shaft. It is going STRAIGHT through.

2) Nearly everything is spinning slower, back half of the transmission, all the driveshafts, etc.. This lowers losses as well.

Makes perfect sense. I would have never guessed it in a million years.

Now on my 13 speed if I ran in 7h (non-overdrive) at 55mph would I see even better mileage or do I just need to keep doing 60 in 8h?

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Originally Posted by allan5oh

Yes that will be overdrive.

You would need to put a direct drive in there AND change the gearset.

If you didn't you'd be at 2100 rpms at 60 mph :P, or 1931 at 55 mph.

You have a 11.1L detroit correct? What are you getting for fuel mileage currently?

Do you find the revs are too high? 1450 sounds good at 55 for that engine.

2.93's would put you at 1380 at 55 mph (with direct drive swap as well)

3.08's would put you at 1451 at 55 mph (again with direct drive)

I'm getting 7.2 (last I checked 2 months ago) loaded, and 10.7(also two months ago) empty. It seems to be doing even better now with the new tranny/tires,..I'll check it next week when I head out.I wanted to change the drive train when I got the new tranny, but it seemed too complicated for the shop to do. My cruise control stopped working 50 miles after I left their place the last time.
I don't think there are any issues with my diff's even though they have 980,000miles on them. They came with synthetic gear oil and don't leak, so I'm probably better off keeping the truck with stock spec's.
I have the 11.1 and 1450 is the lowest I can run this engine,..it falls flat if I drop below that rpm. Its running a bit hot, but I think thats because the engine can't breath through the single muffler, I put on duals and it seems to like the less restricted exhaust. I might also get a fairing for the roof, to help the air up over the sleeper. There's a 17" high wall for the air to hit above my cab.
I toyed with going with a taller 22.5, but still decided to stay with the trucks stock spec's.

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Originally Posted by marylandkw

Possibly. Find out if on your transmission if 7h is direct drive or not.

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Originally Posted by Doghouse

There's a 17" high wall for the air to hit above my cab.
I toyed with going with a taller 22.5, but still decided to stay with the trucks stock spec's.

Doghouse, put a fairing on it! That is the single best way to improve fuel mileage (if you mostly pull vans). Way more than slowing the engine down a little. You should see 0.3 - 0.5 mpg improvement. More if you're still running 68 ar more.

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Originally Posted by eighteenspdjammer

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Originally Posted by Doghouse

There's a 17" high wall for the air to hit above my cab.
I toyed with going with a taller 22.5, but still decided to stay with the trucks stock spec's.

He pulls flatbed.

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Originally Posted by allan5oh (Post 380786)

What you want to do is have a direct drive with a certain gearset that allows the same overall gearing as a regular transmission.

I'll explain:

Truck one, 10 speed direct drive, 2.64's

Truck two, 10 speed overdrive, 3.55's

These trucks have the same tires. Every gear will be within 1% of each other(overall ratio) and the cruise rpms will be the same. You're giving up gearing at the diffs, but you have more at the transmission.

The two advantages are:

1) Power is going direct through the transmission. No power is going through the two countershafts, then back to the output shaft. It is going STRAIGHT through.

2) Nearly everything is spinning slower, back half of the transmission, all the driveshafts, etc.. This lowers losses as well.

The trick is finding a combo that will work for you. If you're hauling more then 80,000 lbs, no go, because there's no direct drive transmission rated for that. Going fast? Again no go, because even 2.64s have too much gearing for going fast(never mind 2.79 or 2.93's). Play in the mud a lot? Not a good idea, because the driveshaft is seeing about 33% more torque.

Basically if you want to do a direct drive setup with efficient tires, you cannot go fast at all, as seen by the chart I posted above. Sure one could go with 11r22.5's, lo pro 24.5's or 11r24.5's but those tires are not as efficient, XDA energy tires are also only available in lo pro 22.5. Super singles are the same diameter as lo pro 22.5's.

You forgot about using an 18 speed with tall rear end ratio. The 18 is more than adequate for heavy loads. You can run in direct (16th) with 2.64 or 2.79 for maximum economy, you have splits into the basement for hard pulls, it has better lower reduction than a 10 or 13 even in reverse, and you still have two more gears up on top that could be used efficiently on flat ground, light loads, no winds, bobtailing, etc. Just spec a drive shaft combo that exceeds what you are putting down by 25-30% and it will handle torque quite nicely.

I looked up the number and a 10 speed direct has a 14.8:1 first compared to a 14.4:1 first on the 18 speed. Not much difference. The problem is I think doing this is useless because the 18 speed simply drags a lot more than a 10 speed ever would. I would consider a 15 speed deep reduction with a 1:1 final over an 18 speed any day of the week, especially hauling heavy. But they don't exist on truck paper. But speccing new they do.