RATIO

Oh trust me, I know...... Starting on a hill is a little sketchy and even on level ground I am starting in bull low whereas my volvo could start in 1st gear..... but 6mpg hauling trains makes up for it when my volvo xe was doing 4.5mpg.

 

For most highway applications of 80,000 lbs or less ACERT C15's were always typically spec'd with 3:36 or higher 3:25's. The older single turbo motors were generally spec'd with 3:55 or 3:70. The single turbo's sweet spot is @ 1,475 RPM. ACERT's sweet spot is much lower. They'll suck more fuel at 1,475. When they (ACERT) first came out lots of guys were complaining of poor fuel mileage, one of the reasons being they were running the RPM's too high. And some were spec'd wrong with 3:55 or lower.

 

Fuel economy has a lot to do with how hard you're working an engine. Low engine RPM does not automatically equal burning less fuel. If you've got tall gears in the back but you have to keep your foot in it just to maintain speed on the flat, you're gonna burn more fuel.

 

Makes sense as to why my pete doesso well. even with 140k, I never have to floor it and never really need to take it over 1650 ever...... unless I'm showing off.

 

Lower RPM equals better fuel economy with an ACERT but not with the single turbos.

 

It's all them compounding turbos. alot of the major engines are running them now. the new volvo engines will be able to lug down to 900rpm due to compounding turbos.

 

A truck geared for the job , will be the most fuel efficient.