good ratio for mpg

But also that Volvo in the fine print states that optimum cruise RPM for the D13 is 1200-1500 RPM. Just because peak torque is at 1050 does not mean that it is within the most efficient RPM of the engine. Detroit makes the same general guideline with their DD15. The lower peak torque applies primarily to starting ability, not general cruise.

Volvo.... across the entire D13 platform... 1200-1500

http://www.volvotrucks.com/SiteCollectionDocuments/VTNA_Tree/ILF/Products/D13/D13 Family.pdf

Detroit... across the entire platform.... at general cruise speed : economy 1300 RPM / Performance 1400 RPM.

https://detroitads.azureedge.net/DET_84627_DD15_Brochure_WEB.pdf

 

However .... The XE utilized specific software , unlike the rest of the D13 lineup to further lower the "sweet spot" ... Per Volvo.
I guess i should post a link?



That's why i recommend you check on your motor specifics before choosing gearing.


I wouldn't try that with a older Detroit or Cummins motor.... Definitely not a CAT.
.

 

Of course, that all is nice when things are perfect and on very gentle interstate running. If one deals with a lot of other roads than interstate, the dynamics change considerably. But let's assume interstate like the video. Bucking a high wind on something even as moderate as I-80 in western Iowa under a heavy load, find out how much it stays in 12th on the hills running 1150 RPM at 65 mph. More often than not, it will have to drop a gear. And since the iShift has roughly a 300-350 engine RPM spread between gears, that means that the engine RPM at just 62 mph (assuming a 3 mph drop on the hill from 65 cruise to trigger the shift) in 11th with the 2.64 rear ratio mentioned in the video is about 1425 RPM. And that is going to happen on almost every hill from Des Moines to I-29. Frequent Shifts often are less efficient than being in a gear that has the engine at a more optimum RPM for the pulls to begin with. Get off the main interstate stuff, and one will rarely be in 12th, if at all, especially when running heavy.

As I made mention many times... it is all about what one is doing, how they are doing it, and where they are doing it.

The fuel economy king is Henry Albert. Even with the latest Detroit DD15 tied up with the Detroit DT12 (which shares virtually the same gear ratios and features of the iShift), Henry has averaged in the high 9 mpg category on runs from California to N. Carolina, with roughly 75K lb gross. And the RPM range he does this at? 1375-1425 cruising at around 65 mph. I have seen similar numbers from good Volvo drivers, also running in the 1300-1400 RPM range on the D13 with similar gross and routes.

There is good reason why both Volvo and Detroit state in their specs sheets on their engines that optimum balance at cruise speed is in the 1300-1400 RPM range.

 

I would recommend you drive one a while before making assumptions on how it runs.....just saying
I own one and you would be very surprised at how little it has to drop out of the top hole (od)pulling grossed out.

Honestly , i was very skeptical of Volvo's XE but now that I've driven it I'm totally a believer. It's very well engineered...

XE is not the standard engine spec , otherwise you would gear for 1325-1350 at cruise with a standard D13


As i said... Don't try this with your average Detroit or Cummins

 

Trying an average Cummins? They had been doing smart advantage packages for isx15 mated with 10 sp ultrashift, either direct or small step overdrive. The 2016 volvo daycab I drive at fxf has that stuff. 1200 rpm at 65 mph at 10 th gear and this is because they specd them with small step overdrive.

 

Correct , your average Cummins , Detroit or Volvo rating aren't designed to operate at the low rpm like XE Volvo or X15 Cummins motors...etc.
They are specifically designed to work in a downspeed powertrain...and they pull like crazy at ultra low rpms.

If you can flash a low rpm software in your specific engine then you're golden to downspeed.

The 10spd ultrashift isn't in the same realm as the DT12 or iShift either though...but that's another topic.

 

Take notes people this guy knows what he's talking about.

Very good post cowpie.

 

@Cowpie1 Can i get some help on gears to? I have a 97 379 pete that has a tuned up 12.7 detroit 3.70 rears lp 22.5's and a rtx10 speed. The truck came spec'd this way but with tall rubber and 24.5's so right now as i sit im 5mph behind where is should be traveling down the road i.e. 70mph on speedo is actually 65 mph in reality. Im looking to do a 13 or 18 speed swap for being able to split the top side on a couple small hills i run, other wise im run pretty flat ground between where i live and phoenix az. This is a dedicated run that i do. Now my question is do i keep my 3.70 rears and go back to tall 24.5's and a 13/18 or do i stay with my lp22.5's a 13/18 and say 3.36 rears. As it sits im running around 65mph at 1500 rpm or so and if i want or need to go any faster i get up into the 1600-1700 rpm range. Id like to be around 70-72 mph and 1500 rpm going down the interstate. What would you suggest?

 

I run heavy in the Northeast...105000 on 5 axles. Running 24.5 tall, 550ISX (2050 torque), 20918B, with 3.73