Torque vs. Horsepower

thgoodman wrote:
My '06 Beaver Patriot Thunder has a C-13 Cat rated at 525hp. The guy parked next to me last week had a similar size MH (looked like a Prevost but wasn't). It also had a Cat C-13 but it was rated at 475hp but with more torque. I know Cat can change engine ratings both mechanically and electronically (i.e., injector timing?) but I don't know why the coach builders' design specs call for different ratings.

What I don't understand is how the torque/horsepower trade off affects vehicle performance and if there would be any advantage to going back and paying Cat to making a change to my engine specs (what would I ask for?). How do the changes affect hill pulling, towing, city vs country driving, fuel mileage, etc? Could the average Joe sitting in the driver's seat even feel the difference if the modifications were made?

I'm surprised at hp being lower and torque being higher. The most common occurrence is for them to increase together but torque at a lower rate than hp. Many times the torque rating will be the same over 2-3 hp ratings. This particular situation may be due to a design change in the fuel system or electronic controls.

Torque and hp are linked. The actual force measured on an engine test stand or a chassis Dyno is torque and the hp is calculated from that. The big "heavy hauling" performance advantage a diesel enjoys is due to the much lower rpm range that a diesel produces both torque and hp. Your C13 likely develops peak torque at around 1200 rpm and peak hp at 1700. The torque curve will stay pretty flat up to 1500 rpm or so at which point the hp will be at 85-90% of peak. Your 6 speed Allison 4000 multiplies available torque and enables the rpm to stay in the sweet spot over a large mph range.

My guess is that you would notice very little benefit in a re flash to increase your power.