[RockyMtnRay]

Originally Posted by Cobra500

I have to disagree a bit- monster torque is great for towing if you do not want to shift to a lower gear and economy is not an issue. Transmissions are built to trade convert hp (high rpm) for torque- they are really torque multipliers. Variable timing provides an aid for an engine to produce good torque numbers in both high AND low rpm ranges, not either/or like conventional camshaft timing. In reality, it is better for the engine to shift down to a higherr gear (to pull a long grade) than to lug the engine.

Actually we are in agreement on the general prinicipal...it's a matter of specifics about the exact RPM and exact gear ratio, and the length/steepness of the grades.

As someone who does mostly mountain towing (I don't think I've ever towed more than 10 consecutive miles on truly flat terrain), my views are this:

• To avoid downshifts (or torque converter clutch unlock) on even slight grades, you should tow in the gear that gets the engine close to its peak torque RPM at the preferred highway towing speed (typically around 65 mph). For most engines in the 250 to 350 ft lb range, that means using direct drive (OD off) on an automatic so the input/output is a 1:1 ratio...IOW 3rd on a 4 speed with OD transmission, 4th on a 5 speed with OD transmission. And that in turn means an engine RPM around 2500 to 3000.
• Towing with the engine turning way below its peak torque RPM is indeed lugging it.
• Having lots of low end torque means that downshifts to 2nd on a 4spd; 3rd on a 5spd can be avoided on grades of under about 5 or 6 percent. A downshift to 2nd or 3rd means engine RPM of 4000 or higher and that's neither comfortable to occupants nor good for the engine on a long term basis. Sure, on a long, steep, high altitude grade such a downshift is probably unavoidable and not harmful for a few miles. But having such downshifts on every slight incline is not good for the transmission.

I've spent the last year or so (and about $3000) improving my truck's low/midrange torque and ability to avoid downshifts to 2nd gear while towing on anything but the steepest and highest altitude mountain grades here in Colorado. I'm very happy with my results and feel the money was well spent. Keeping in mind that I'm towing at altitudes from 5000 to 12,000 feet, downshift frequency while towing has diminished from an almost-every-moderate-climb to just-the-seven-percent-and-up grades. Sure, I could have bought a more powerful truck to begin with...but none of them would fit in my garage. And none would have had Toyota's reputation for reliability.

The only red flag Id have regarding some of the Jap/Euoropean peak-HP wonders involves turbocharging. Towing is murder on a turbocharged GASOLINE motor (diesel motors tow very well with turbocharging...). The problem involves heat generation and detonation, a devestating byproduct of high heat.

Heartily agree.