23.71mpg last tank (also RPM question)

[Jeepmullet]

67mph 2650rpms in 5th gear, unloadedm 98% highway driving, worn tires, same mods as in signature except I changed my air filter to the spectre one that's supposed to flow 900cfm (which is $40 at autozone, jury is still out on its filtering capabilities)



The approximate elevation change for the trip was less than 400 feet. I started at 126 feet at bastrop louisiana, and ended in Conway Arkansas at 560'. Short trip, and I filled up before I left and when I got back. I went 166 miles and put 7. 005 gallons in. Not a full tank I know, but I think I've found the sweet spot for driving unloaded



Is it okay to drive at 2650-2700 rpms for hundreds of miles? The truck didnt feel like it was having to pull hard to keep those Rs or that speed. The pyro read 475* and boost was around 2lbs or less (hard to tell, it was barely off the needle)

 

[LOtero]

wow, rpms seem kinda high... maybe its just me

 

[Jeepmullet]

wow, rpms seem kinda high... maybe its just me

I know, I guess the higher RPMS = higher hp = more inertia (shaddup rusty, dont cherry pick here) = less need for boost = less fuel = lower boost = better fuel economy?



6th gear just doesnt get good fuel economy unless I'm going over 73mph.

 

[Jeepmullet]

I wonder if I can switch to 285/75s and keep nearly the same fuel economy in 5th at 70mph since it will be close to the same rpms.

 

[Cummins Thunder]

475 on the pyro!!!! I think you need to get that thing checked out



BTW, you must of had one helluva tail wind!!!! ~2lbs of boost??????

 

[Jeepmullet]

475 on the pyro!!!! I think you need to get that thing checked out

I know, i need it to be at least 1200 everytime I hit the pedal.



The pyro moves fine and I cant even get it to 1100 pulling my trailer up a hill at 90mph. My trailer only weighs around 3k lbs.

 

[Jeepmullet]

going up hills the boost got as high as 15 sometimes. The overhead console was reading 29. 3mpg. It said I had a range of 840 miles too!

 

[Cummins Thunder]

My truck will make 2 lbs of boost in NEUTRAL turnin 2700rpm... And thats with a 21cm exh housing!!!

 

[nickleinonen]

Is it okay to drive at 2650-2700 rpms for hundreds of miles?

yes... that is right at the rpm limit for the industrial application isb engines. and they run at that for 1,000's of hours straight [unloaded and loaded]

 

[VicR]

Interesting observation. The sweet spot for mileage on my 99 is about 2100 RPM, which is about 73 MPH. However I have a SO 6-speed, so the power curve is different I think.



-Vic