The Definitive Torque vs. Horsepower post
Year after year, I keep seeing the same old debates about torque vs. horsepower. Everyone seems to have a general idea that we are referring to power, but most don't really understand the relationshi...
Forum Discussion
Low rpm horsepower, aka torque, reduces your need for gearing. But in the end the amount of power at the wheels is what matters.
Quick analgy. Numbers are mythicals for purposes of the explanation.
Engine 1 makes 100 hp at 1,000 rpms
Engine 2 makes 100 hp at 10,000 rpms.
Engine 1 makes 525 ft/lbs at 1,000 rpms.
Engine 2 makes 52.5 ft/lbs at 10,000 rpms.
Okay, so lets assume that the vehicles are loaded the same but with different gearing. Engine 1 is geared to run 60 mph at 1,000 rpms, and Engine 2 is geared to run 10,000 rpms at 60 mph. Both are using the same size tire, lets say 245/70R19.5 which is 624 rev/mile.
So the gearing. Engine 1 needs a final drive ratio (trans and diff combined) of 1.605:1, making the torque to the wheels 842 ft/lbs.
Engine 2 needs a final drive ratio of 16.025:1, making the torque to the wheels 842 ft/lbs.
There you go, 2 engines with the same hp rating and very different torque numbers. They both will hold the exact same speed on the hill.
Based on gearing they could both accelerate the same.
The difference between that example and modern gas vs diesel is that the gearing between gas and diesel is too close. The gas engine may actually make more hp (my year truck the Hemi had 50 more hp than the diesel), but with the gearing the way it is the Cummins can make more hp sooner and on average.
If you where to gear the gas truck to run in the power band where it makes all it's torque (and thus hp) it would do better, and be screaming when power wasn't needed and thus get even worse economy or have a lot more gears (hence the new 8 speed auto transmissions).
High torque to hp means low rpm operation, which means a lower rpm towing experience.
Quick analgy. Numbers are mythicals for purposes of the explanation.
Engine 1 makes 100 hp at 1,000 rpms
Engine 2 makes 100 hp at 10,000 rpms.
Engine 1 makes 525 ft/lbs at 1,000 rpms.
Engine 2 makes 52.5 ft/lbs at 10,000 rpms.
Okay, so lets assume that the vehicles are loaded the same but with different gearing. Engine 1 is geared to run 60 mph at 1,000 rpms, and Engine 2 is geared to run 10,000 rpms at 60 mph. Both are using the same size tire, lets say 245/70R19.5 which is 624 rev/mile.
So the gearing. Engine 1 needs a final drive ratio (trans and diff combined) of 1.605:1, making the torque to the wheels 842 ft/lbs.
Engine 2 needs a final drive ratio of 16.025:1, making the torque to the wheels 842 ft/lbs.
There you go, 2 engines with the same hp rating and very different torque numbers. They both will hold the exact same speed on the hill.
Based on gearing they could both accelerate the same.
The difference between that example and modern gas vs diesel is that the gearing between gas and diesel is too close. The gas engine may actually make more hp (my year truck the Hemi had 50 more hp than the diesel), but with the gearing the way it is the Cummins can make more hp sooner and on average.
If you where to gear the gas truck to run in the power band where it makes all it's torque (and thus hp) it would do better, and be screaming when power wasn't needed and thus get even worse economy or have a lot more gears (hence the new 8 speed auto transmissions).
High torque to hp means low rpm operation, which means a lower rpm towing experience.
