What does rear ratio in a semi means?

Yes that’s fine.

 

It is fine. Nothing wrong with that set up.

 

Lugging the engine doesn't get you up the hills. Without considerable slowdown.

Power gets you up the hills.

You can do Phoenix to flagstaff 30 minutes faster at 1700 rpm over 1300 rpm. You also keep the engine cooler with faster fan speed. And burn less fuel.

 

Yeah, if I'm on flat ground I'll run the rpm higher because that's what my engine is built for. But for climbing I tend to keep it at 1500 for peak torque, no matter which gear I'm in. If I see the rpm dropping below 1500 when I'm climbing, I'll downshift immediately. My rpm drop like a lead balloon if my gear is too high for the climb.

 

Haven’t you been driving local for a number of years? Or do you actually have experience driving new engines on I-17? Because I do, and I can tell you that I know make it up that stretch of road faster with my 12 speed letting it do what it does than I did with my 18 speed driving how I thought I should and keeping it at 14-1500 up through the hills. Also the Cummins and Paccar engines (not sure about Volvo and Detroit) have variable speed fan drives that run the fan based on the cooling needs of the engine, so RPM has no bearing on the speed of the fan anymore unless you run with the switch on which isn’t needed at 80k gross.

Torque is a constant and horsepower is based on repeating the same action multiple times. What was the torque of the engine you had when it was at 1700 rpm? What did the torque curve look like? Chances are it was an older engine and not designed to sit in a low rpm range anyway. If I drove my current truck at 1700 rpm the output would be roughly 450ft lbs of torque less than running it where it’s designed at 1100rpm. So I would be trying to overcome giving up 450ft lbs of torque by spinning the rpm higher for a few extra HP.

 

And these would be the new engines that get rebuilt at 500k….?

there’s nothing like 700ish/2250ish to get you up any hill…

 

Idk. My last one had 600k on it when I sold it and it’s still hauling milk here locally.

 

These newer engines must have beefier bottom ends compared to the older engines that didn't like to be lugged? I would think so

 

I Had a new 16 FL with the last company. They were western regional.

Regardless. Lugging the engine requires heavier throttle.

 

Pretty much everything now is designed around a lower rpm. That’s how they are getting the fuel economy numbers that they are. Most days I cruise at 1150–1200 or so and that’s high compared to the Volvo guys who can run 1000 or lower at cruise.