2.64 with 13 speed double-over & 22.5 LP

10 speed is more then likely a direct,, post the model number.

I still don’t get why guys love these useless gears you can’t pull much more then an empty trailer with….. even getting it set up right, it will never break even on the swap

 

You’ll be swapping that ISX shortly

 

Any shop with Cummins software can fix the speedometer issue. Computer just needs to know the new rear ratio. Should have been done by the shop that changed it.
The ISX is not a downsped engine. Probably should run in the 13-1400 rpm range. Means you’ll likely never use the top two gears except when empty or going 80 mph.

 

I am not exactly sure what caused your problem, but that gear and transmission combination works fine when everything is set correctly. I had built and have successfully been operating a 2:64 in a Series 60 Detroit, 18 speed with 22.5 low pros for the last 8 years. I generally run 65 mph in 16 @1550 RPM and it pulls like a mule. It gets slightly better than average fuel mileage for my application which has terrible wind resistance and bad aerodynamics. 5-5.5 is my loaded mpg and 7 when empty which is normal for a carhauler. Yours would be roughly the same RPM’s in 12th as mine in 16 if your motor and tires were the same as mine. I figure my fuel mileage with a calculator and not the dash because my truck always thinks my fuel mileage is different than my actual mileage.

 

A former TTR member who isn’t with us anymore called cowpie ran that setup but with a 18 speed his isx didn’t mind it and returned great fuel mileage.. he ran in 16th gear he loved it so much he setup up hiis glider with a 500 hp series 60 18 speed and 2.64 . 16 th loaded is equivalent of 3.55 double over at highway speeds. Empty you can use 17 th if you’re in a rush.

 

Your fuel mileage is off because your speedometer / odometer is off. Get everything recalibrated and try again. There’s no reason you can’t run the truck down the road in 11th and get decent fuel mileage. If you swap the 10 speed direct into it then you could also end up doing a bunch of driveline work of the trans housings aren’t exactly the same.

 

i was 5.84 last quarter on 11r22.5 and 3.55s hauling chunky in the north east….

 

If the odometer is off accordingly with the speedometer, you’re actually getting 5.6 mpg. That’s a start. Final drive is the same in 11th as the 10 spd. at 1-1. Assuming it was a direct 10. Any difference might have more to do with driving habits. Try keeping your foot out of it, be patient, giving it time to slowly wind up, take advantage of splitting the 13, especially when heavy, splitting down on hills early enough and avoid lugging, instead of just mashing the pedal and picking up the load. The ISX has a lot of torque, assuming the odometer is off, you’re only down 8% not 33% on mpg’s. Running at lower rpm’s is only good to a point. Once below the most efficient rpm, it becomes a drag on fuel economy, puts extra wear on driveline. Everything except the rear’s ironically.

 

I put 3.08 in front of a 13 spd and ISX. It’s really a game of boost pressure not rpm. Remember you basically double your fuel consumption every 14lbs of boost. So at 30lbs your burning 200% more fuel than at 0 boost at cruise.

so in my opinion you’ll never when this game with out a boost gauge.

 

Are you running a carhauler or OD freight? 90 feet of turbulence is the difference in 5 something loaded and 7 something empty.