Horsepower or Torque - the question...

["Mad Max"]

Okay fellas - I've got one for ya:



On our rigs, which part of the RPM band would be most likely to produce the best fuel mileage?



Considerations - Gearing, tire size, weight, speed, and go pedal discipline. Now, I'm using my rig as a baseline, so here are my specs and questions:



93 D250 club cab, 3. 54's, 235 85/16's, no pump or exhaust mods (yet), 70-75 mph, highway cruising unloaded, right foot 'ordered' to go easy.



As I understand, torque gets you up to speed and HP keeps you there. My question is, would I want to keep the truck in its torque curve (~1700 rpm) or HP curve (~2000) rpm, to net the best mileage at those speeds, and would there be much of a difference?

Lower RPM typically means less fuel being consumed so in theory better mileage as long as the engine isn't laboring to maintain speed. I would think you would want to maintain good turbo pressure at the rpm you want to cruise at to ensure the engine isn't lugging or laboring unnecessarily - that means designing the intake/exhaust and chassis to make the most efficient power at the RPM you want to cruise at most of the day, yes?



For me, I'd like to cruise at about 1700 RPM whle on the highway doing about 75 mph - nice and easy. I am looking at a GearVendors od to bolt to the back of the NV4500 I'm eventually swapping to, and at this point I'm really wanting to know if the 300 rpm or so diference would be noticable - I'm not asking if it would be worth it, but only if the mileage would be better at 1700 RPM with my size rig?



(Whew) That was hard to type - hope my question makes sense, but I've been wondering about the HP -vs- TQ theory for a long time.

Thanks peoples,

- Sam

 

[JFitzgerald]

Sam, my understanding is that the best volumetric efficiency occurs at peak torque. I've read here before about people basing their pursuit of mpg on cruising at peak torque rpm. Makes sense in my small mind.

 

[Bob Beauchaine]

I am running 3. 54 gears in my rear diff and when I run a steady 70 to 75 mph I average 21 to 22 mpg. At 55 I would probably get 23+ mpg but thats just too darn slow. You can look at my sig for mods. I have always beleived that the right foot is the key to the best mileage. Depending on speed I am right in between 1700 and 1800 rpm.



Bob