Horsepower is horsepower?
If that theory is true (in real circumstances), then a 385hp 6.7L Cummins diesel shouldn't spank a 381hp Toyota Tundra when both are tested 0-60 towing a 5740# boat. But it did. Must be the adva...
Forum Discussion
There's sure a lot of hot fuel vapors being blown around in this discussion - along with a few truths!
For lack of a better format, here's a summary list IMHO of some of the basic realities arising out of this discussion:
1) The classic equation everyone keeps throwing around, Horsepower = (Torque X RPM) / 5252 ... can easily be rewritten as Torque = (Horsepower X 5252) / RPM. So you see ... an engine's crankshaft torque indeed does depend upon how much horsepower the engine is putting out.
2) Hence horsepower is horsepower ... or alternatively ... torque is torque. It depends upon how you want to look at it to serve your own purpose(s).
3) An engine's crankshaft torque doesn't mean anything ... unless you need to plug it's value into the classic equation in order to see how much horsepower a particular engine is putting out.
4) It's how much torque is trying to twist the drive axle(s) at any particular vehicle speed with any particular load that means something.
5) How you get a particular amount of torque trying to twist your drive axle(s) at any desired vehicle speed is through overall gearing that converts the required amount of horsepower of the engine available at a particular RPM of the engine.
6) This conversion of engine horsepower into drive axle torque takes a gearing process, whether the engine be diesel or gasoline.
7) Hence, an XXX horsepower gasoline engine can be made to do the same thing as an XXX horsepower diesel engine ... assuming both engine types are fed "via air of the same density". In other words ... it's no fair comparing a boosted air pressure engine of either type to a non-boosted air pressure engine of the other type. For example, a turbo diesel must only (fairly) be compared to a turbo gasser, or alternatively, a non-turbo diesel must only (fairly) be compared to naturally aspirated gasser.
8) Then ... what's really the difference between the two engine types?
- Diesel fuel contains somewhere in the neighborhood of 30% more energy per gallon, hence theoretically "all other things being equal (ncluding price per gallon)" a diesel setup can be made to deliver more work per gallon of fuel than can a gasoline engine using gasoline. Unless diesel fuel is too much more expensive than gasoline, a diesel engine's fuel costs thus runs lower than that of a gasoline engine - given both engines of the same horsepower.
- The diesel process takes very high cylinder pressures, so they weigh more due to the amount of material required to make them strong, and they usually cost more due to this required strength.
- The diesel fuel burning process takes place best at lower engine RPM, so they turn a lot slower while putting out their horsepower.
- Due to the diesel lower RPM and stronger material to withstand the higher pressures, diesel engines used to outlast gasoline engines.
- The above is no longer so much the case. Modern mass production manufacturing processes, especially since about the mid-1990s, can produce gasoline engines that last of hundreds of thousands of miles.
- Since gasoline contains less energy per gallon, more gallons per hour of gasoline must be burned by a gasoline engine of XXX horsepower to produce the same energy as a XXX horsepower diesel engine. Hence, gasoline engines usually have to spin at higher RPMs per unit of horsepower than diesel engines spin per unit of horsepower.
- The lower spinning speeds of diesel engines probably give a lot of confidence to their owners because it doesn't sound to them like the diesel engine is "going to blow itself apart" while it's producing it's horsepower. A gasoline engine producing the same horsepower turns faster for a given horsepower - thus perhaps sounding like it's closer to breaking itself. Modern overhead cam, well balanced and well muffled gasoline engines can standup to running hour after hour and year after year at their required higher spin speeds.
- Many modern gasoline engines are now geared with many more ratios being available in their transmissions so as to be able to keep them in their high horsepower bands throughout a variety of vehicle speed and towing conditions. This means less slow speed "lugging along" is necessary with a modern gasoline engine than what used to be the case with only a simple 4-speed transmission behind the gasoline engine.
- A diesel gets more horsepower by mostly (not much RPM change) just cramming more fuel into each cylinder per minute via the driver pushing in the pedal more with no vast speed-up of RPM required. Whereas, a gasser must produce more horsepower by increasing it's RPM (a lot of RPM change) to burn more fuel per minute via the driver pushing in the pedal more.
- Hence a diesel may "seem like it's pulling better" because less radical gear changes are required, less RPM noise is experienced, and no feeling is created of "an engine about to destroy itself".
- Still ... in the U.S. ... gasoline is more readily available in more places during more hours than diesel. Hence gasoline refueling is still less worrisome on long RV trips involving travel in out of the way places off the Interstate highway system.
The Ford Eco-Boost technology happens to include boosting/evening-out pf incoming air density, thus making it's horsepower fall off less at high altitudes - just like with turbo boosted diesel engines. It's just that boosting of small truck diesel engines happened earlier, small truck market-wise, than boosting of small truck gasoline engines. Of course super-charged gasoline engines have been around for years - just not offered by the high volume U.S. truck manufacturers - and supercharged gasoline engines can be made to maintain their horsepower at high altitudes.
FWIW, I'll keep my very quiet and smooth running V10 RV engine. So far, it's pulled fine at 9600 feet and diesel RV tow vehicles did not pass me up on the high altitude highways in Eastern Wyoming. However, I do have to accept running it for miles and miles in the 4000-5000 RPM range - which many diesel RV drivers would not tolerate.
For lack of a better format, here's a summary list IMHO of some of the basic realities arising out of this discussion:
1) The classic equation everyone keeps throwing around, Horsepower = (Torque X RPM) / 5252 ... can easily be rewritten as Torque = (Horsepower X 5252) / RPM. So you see ... an engine's crankshaft torque indeed does depend upon how much horsepower the engine is putting out.
2) Hence horsepower is horsepower ... or alternatively ... torque is torque. It depends upon how you want to look at it to serve your own purpose(s).
3) An engine's crankshaft torque doesn't mean anything ... unless you need to plug it's value into the classic equation in order to see how much horsepower a particular engine is putting out.
4) It's how much torque is trying to twist the drive axle(s) at any particular vehicle speed with any particular load that means something.
5) How you get a particular amount of torque trying to twist your drive axle(s) at any desired vehicle speed is through overall gearing that converts the required amount of horsepower of the engine available at a particular RPM of the engine.
6) This conversion of engine horsepower into drive axle torque takes a gearing process, whether the engine be diesel or gasoline.
7) Hence, an XXX horsepower gasoline engine can be made to do the same thing as an XXX horsepower diesel engine ... assuming both engine types are fed "via air of the same density". In other words ... it's no fair comparing a boosted air pressure engine of either type to a non-boosted air pressure engine of the other type. For example, a turbo diesel must only (fairly) be compared to a turbo gasser, or alternatively, a non-turbo diesel must only (fairly) be compared to naturally aspirated gasser.
8) Then ... what's really the difference between the two engine types?
- Diesel fuel contains somewhere in the neighborhood of 30% more energy per gallon, hence theoretically "all other things being equal (ncluding price per gallon)" a diesel setup can be made to deliver more work per gallon of fuel than can a gasoline engine using gasoline. Unless diesel fuel is too much more expensive than gasoline, a diesel engine's fuel costs thus runs lower than that of a gasoline engine - given both engines of the same horsepower.
- The diesel process takes very high cylinder pressures, so they weigh more due to the amount of material required to make them strong, and they usually cost more due to this required strength.
- The diesel fuel burning process takes place best at lower engine RPM, so they turn a lot slower while putting out their horsepower.
- Due to the diesel lower RPM and stronger material to withstand the higher pressures, diesel engines used to outlast gasoline engines.
- The above is no longer so much the case. Modern mass production manufacturing processes, especially since about the mid-1990s, can produce gasoline engines that last of hundreds of thousands of miles.
- Since gasoline contains less energy per gallon, more gallons per hour of gasoline must be burned by a gasoline engine of XXX horsepower to produce the same energy as a XXX horsepower diesel engine. Hence, gasoline engines usually have to spin at higher RPMs per unit of horsepower than diesel engines spin per unit of horsepower.
- The lower spinning speeds of diesel engines probably give a lot of confidence to their owners because it doesn't sound to them like the diesel engine is "going to blow itself apart" while it's producing it's horsepower. A gasoline engine producing the same horsepower turns faster for a given horsepower - thus perhaps sounding like it's closer to breaking itself. Modern overhead cam, well balanced and well muffled gasoline engines can standup to running hour after hour and year after year at their required higher spin speeds.
- Many modern gasoline engines are now geared with many more ratios being available in their transmissions so as to be able to keep them in their high horsepower bands throughout a variety of vehicle speed and towing conditions. This means less slow speed "lugging along" is necessary with a modern gasoline engine than what used to be the case with only a simple 4-speed transmission behind the gasoline engine.
- A diesel gets more horsepower by mostly (not much RPM change) just cramming more fuel into each cylinder per minute via the driver pushing in the pedal more with no vast speed-up of RPM required. Whereas, a gasser must produce more horsepower by increasing it's RPM (a lot of RPM change) to burn more fuel per minute via the driver pushing in the pedal more.
- Hence a diesel may "seem like it's pulling better" because less radical gear changes are required, less RPM noise is experienced, and no feeling is created of "an engine about to destroy itself".
- Still ... in the U.S. ... gasoline is more readily available in more places during more hours than diesel. Hence gasoline refueling is still less worrisome on long RV trips involving travel in out of the way places off the Interstate highway system.
The Ford Eco-Boost technology happens to include boosting/evening-out pf incoming air density, thus making it's horsepower fall off less at high altitudes - just like with turbo boosted diesel engines. It's just that boosting of small truck diesel engines happened earlier, small truck market-wise, than boosting of small truck gasoline engines. Of course super-charged gasoline engines have been around for years - just not offered by the high volume U.S. truck manufacturers - and supercharged gasoline engines can be made to maintain their horsepower at high altitudes.
FWIW, I'll keep my very quiet and smooth running V10 RV engine. So far, it's pulled fine at 9600 feet and diesel RV tow vehicles did not pass me up on the high altitude highways in Eastern Wyoming. However, I do have to accept running it for miles and miles in the 4000-5000 RPM range - which many diesel RV drivers would not tolerate.
