sweet spot on 3.55

[daveshoe]

I have a long wheel base cab @ chassis that has a 8' wide x 10' long utility bed with the aerodynamics of a brick. The first tank of fuel got 16 MPG. After the bed was installed it dropped to 15 MPG. This bed weighs 2000 LBS and tools add another 500 or so. Total weight ready to work is 9500 LBS. Most trips to work are between 10 to 30 miles.

I have been reading about sweet spot and most guys seem to think 2200 is about the place to run these trucks.

I was comparing my truck to a neighbors 3500 and noticed my tires were 2'' taller than his . Is this because cab & chassis run taller tires than standard?

I just can't seem to force myself to run at 2200 RPM. The truck has decent power at 1550 in sixth gear running at 55 MPH. To run at 2200 RPM I would be running 59 MPH in fifth gear or 79MPH in sixth.

MY main Question is do you guys think I am hurting fuel mileage running like this? Truck is stock 02 3500 with 6600 miles.

 

[jlccc]

Originally posted by daveshoe

MY main Question is do you guys think I am hurting fuel mileage running like this? Truck is stock 02 3500 with 6600 miles.

No, you're not hurting mileage. My truck gets its best mileage at 55-60 mph. At 65mph I lose 1mpg, at 70 about 1. 5mpg and at 75 I've lost 2 to 2. 5 mpg. I have an '02 with the six speed, 3. 55 axles and 265 tires.

 

[WadePatton]

I'm the one always going 79mph in 6th!



I feel that there are too many variables in this equation to nail absolutes on a couple hundred RPM.



I suspect the tire size difference you noticed is 245's vs 265's. You could run the 245's and get your R's without going too fast. But them tires ain't cheap so that might take a while. Or maybe swap with somebody who wants to try "big" tires.



I've only seen two big jumps in my regular daily driving mileage. Once was when the LP was weak and I didn't go past 3/4 throttle for a whole tank The other was the first tank I treated with cetane enhancing fuel additive.



see thread: https://www.turbodieselregister.com/forums/showthread.php?threadid=31358



An EZ box or 275 injectors are reported to help mileage out too, but then we start down the BOMBing road... and gosh, I don't want to be blamed for leading you down that path!

:-laf



And hey, give that puppy 20-30,000 miles to loosen up a bit! (break-in)

 

[slo-ryde]

15 mpg sounds pretty good for the weight and aerodynamics you mentioned. I've forgotten most of what I learned in school but I do know that the faster you go the more drag, and that means the gas mileage is going to go down because the motor is working harder to overcome it.



I met up with a fellow with a 2500 lwb and a very large cabover camper on it. He gets 10 to 12 mpg with the camper and 19 to 20 without it. I didn't ask how much it weighed. It probably has similiar frontal area to your truck.