Fuel Efficiency Older vs New

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I think as much of the fuel economy is in the driver’s foot as is in the drive train. I know a fellow that runs a 1985 Peterbilt 359, with a 3406 B and a 6+4 transmission, and he gets 7-7.5. I also know some guys that can’t get more than 4 out of a B.

 

I had an 01 pete with a 700ish HP cat and 3:70s. Now have a 15 W900 with ISX 525hp and 3:55s.
Not much difference in Fuel economy, but the pete was better and more fun to drive.
But I do short hauls in a hurry. avg around 3.7mpg

 

it's more the truck and the driver and what you are doing than the engine

 

Went from 3406 e 2ws 550 to 565 2050 x15 performance. Cummins gained .4 mpg.

 

But drank up the gain with DEF?

 

wait till the failures…….

 

Under 80k GVW? The old school 12.7 liter factory 500HP Detroit. Hands down the overall best performer when it comes to both pulling and fuel economy.

 

That is the case. 3406E is a much more economical move. X15 is an expensive engine. Buy a turbo, egr cooler, turbo module, or anything..

 

Mpg is far more dependent on the driver than any other factor…
I have 2 identical daycabs there one vin apart and one esn apart they are m11 celec engines I can get mid 5s out of either one pulling a end dump I have a driver that will struggle to get 4 out of either one even if they’re both on the same job I guess it’s worth it…he’s never tipped one or had any type of accident and usually gets 1 or 2 more loads in a day. All this being said I have had both 3406b and big cam Cummins in other day cabs and have had similar mpg. Typically the big cam got better mpg than the b model but not enough to make me prefer them.
I have a customer who runs a 3406e making 800hp and 3200ftlb on the wheels and he gets 5.5-6 he recently sold that truck and now has a 12.7 Detroit with factory 4xx hp programming and can’t quite hit 6.5 mpg. I can get 6.5-7 out of the cat but I drive it like it’s got 300 hp until I gotta pass some fleet trucks stuck at 66mph. the point of this rambling is it’s primarily a driver habit thing.

 

My Cascadia gets 8.5 to 9 mpg. DD15. I bought it from Pedigree Truck Sales. They have them specced for great fuel economy.