[scottofksu]

I too have been spending an inordinate amount of time considering these issues. I am determining the variables that will comprise the drivetrain for my truck with an eye towards roll-on power and fuel mileage. My interest is to keep cruising RPM's as low as possible (fuel efficiency) without having to downshift or floor it just to get up a small hill (drivability).

My understanding is that you want the rpm at which you typically cruise in your vehicle to correspond to either just past the peak of the torque curve or an area where the torque doesn't drop off dramatically if rpm drops by 200-500 revolutions.

Further, as I understand it, horsepower is essentially the amount of torque that can be applied at a given speed/rpm. As I explained it to a friend, torque is how hard we can push my truck and horsepower is how hard we can still push it after it starts moving at a given speed (i.e., HP = (RPM X Torque)/5252). That is, my understanding is that HP is at least equally important as torque when we talk about how a vehicle operates at speed. Hence, I have heard that you want your cruising RPM to be noticeable below where peak HP is generated, but at a point on the curve that will ensure smooth acceleration. Thus, I have heard it recommended that you want your cruising rpm to be situated between the RPM at which peak TQ and HP are generated. That way, if you encounter a hill, torque increases as speed (RPM) decreases. This is one of the reasons why they typically say you need a lot of low-end torque for heavy vehicles (i.e., the heavier the vehicle the more TQ you need to keep it moving at speed).

Now that I got that out of my head... :0)

Can you give me some more specifics on your engine (Size, MPG, etc.)? The reason I ask, is that I am looking at a cruising rpm of around 1,800-2,000 RPM, with slightly higher geared torque ratings (i.e., torque "to the ground").