A Simpler Explanation Of The Measurement Of ONE HORSE POWER

pnichols wrote:


I've always thought that the diesel owners thought that their rigs pulled better because they didn't have to rev the engine very high to tap the engine's horsepower. Kindof a preference thing, not really based on engineering facts.

The V10 in our small motorhome will paste me back into the seatback if I punch it, but it takes 4000-5000 RPM to do it.

You can get any torque number you want at the wheels through gearing, horespower cannot go up (only goes down through losses from engine to wheels). Gears exchange RPM for torque. Your diesel engine puts out 1000 lb-ft of torque, who cares, I can get 10000 out of a lawnmower engine with the right gears.

You cannot measure power directly, dynos measure rpm and torque to derive horsepower. Torque is meaningless on its own, it requires the rpm component to get a meaningful measurement of power.

Many of those here should recognize this relationship as the same one between volts, amps and watts. Watts are power (746 per hp in fact), volts is equivalent to torque and amps equivalent to rpm. Using a transformer/coil you can exchange one for the other but watts stays the same. Just think your spark plug gets 20000v from a 12v system through a coil, you can get 20000 lb-ft of torque from a 12 lb-ft motor through gears.

Again you don't measure watts directly either, you measure voltage and current to derive power.

wanderingaimlessly wrote:

Boon Docker wrote:
One Horse Power Hybrid



Wonder how many miles per bail?

Wonder which group will protest its emissions? :)

If it's designed properly it could be a hybrid. A small furnace could burn the horse's output to provide heat and zero emissions at the same time.

valhalla360 wrote:

pnichols wrote:

I'm NOT trying to start once again that infamous RV/truck owners' timeless discussion ... BUT: Isn't all horsepower the same? And also don't modern rotating machines merely convert their available horsepower into the required rotating torque at the required location using various gears and driveshafts?

Now here's what I'd sure like to have explained ... why a 300 horsepower diesel RV engine can "tow better" than a 300 hrosepower gas RV engine? That has never made sense to me. :h

Two engines putting out equal HP will tow equally well...this assumes you mean will they be able to exert the same pulling power.

There are a few caviots:
- HP = Torque x RPM, since diesels make higher torque but peak at lower RPM, they sound quieter when producing peak HP due to the lower RPM, whereas the gas engine is fine but it sounds like it's screaming up at 4000-4500 RPM.
- This assumes there is a gear ratio that lets the motor reach peak HP. In the old days of 2...3...4 speed automatics, you often wound up in a gear that didn't let the engine reach peak HP. Modern 6-10 speed automatics largely eliminate this issue.
- Exhaust brakes are an add on that make a diesel more controllable on a downgrade...it can't pull more because of it but it does improve the towing experience.
- It's changed with modern gas engines putting out similar HP to the diesels but in the past, the diesel was typically a HP jump compared to the base 5L gas V8.

Mike ... very well stated ... and about what I thought!

I've always thought that the diesel owners thought that their rigs pulled better because they didn't have to rev the engine very high to tap the engine's horsepower. Kindof a preference thing, not really based on engineering facts.

The V10 in our small motorhome will paste me back into the seatback if I punch it, but it takes 4000-5000 RPM to do it.

pnichols wrote:

I'm NOT trying to start once again that infamous RV/truck owners' timeless discussion ... BUT: Isn't all horsepower the same? And also don't modern rotating machines merely convert their available horsepower into the required rotating torque at the required location using various gears and driveshafts?

Now here's what I'd sure like to have explained ... why a 300 horsepower diesel RV engine can "tow better" than a 300 hrosepower gas RV engine? That has never made sense to me. :h

Two engines putting out equal HP will tow equally well...this assumes you mean will they be able to exert the same pulling power.

There are a few caviots:
- HP = Torque x RPM, since diesels make higher torque but peak at lower RPM, they sound quieter when producing peak HP due to the lower RPM, whereas the gas engine is fine but it sounds like it's screaming up at 4000-4500 RPM.
- This assumes there is a gear ratio that lets the motor reach peak HP. In the old days of 2...3...4 speed automatics, you often wound up in a gear that didn't let the engine reach peak HP. Modern 6-10 speed automatics largely eliminate this issue.
- Exhaust brakes are an add on that make a diesel more controllable on a downgrade...it can't pull more because of it but it does improve the towing experience.
- It's changed with modern gas engines putting out similar HP to the diesels but in the past, the diesel was typically a HP jump compared to the base 5L gas V8.

wanderingaimlessly wrote:

Boon Docker wrote:
One Horse Power Hybrid



Wonder how many miles per bail?

Wonder which group will protest its emissions? :)

Likely the driver of that car. Note the direction the horses butt is pointed....
:B:B

" Torque is constant over the RPM range, while Horsepower is a straight line function of RPM."

So you are saying that horsepower increases with increasing RPM?

If so, then the engine at 5500 RPM makes more HP than the engine at 2400?

larry cad wrote:

Horsepower doesn't convert to torque nor vice versa.

Well actually, it does. HP = Torque X RPM / 5252 and Torque = HP X 5252 / RPM

pnichols wrote:

Housted wrote:
One horsepower equals 550 foot pounds (pound feet) per second.

In high school, in physics class, I generated 1 horsepower by running up a flight of stairs. :)

Housted

I'm NOT trying to start once again that infamous RV/truck owners' timeless discussion ... BUT: Isn't all horsepower the same? And also don't modern rotating machines merely convert their available horsepower into the required rotating torque at the required location using various gears and driveshafts?

Now here's what I'd sure like to have explained ... why a 300 horsepower diesel RV engine can "tow better" than a 300 hrosepower gas RV engine? That has never made sense to me. :h

Horsepower doesn't convert to torque nor vice versa. Torque is constant over the RPM range, while Horsepower is a straight line function of RPM. Thus, the diesel engine, which operates with a typical limit of 2400 RPM produces more torque than a typical gas engine which operates up to 5500 RPM. Another factor that produces torque is larger displacement (BIG pistons)

So one HP is like moving a 550 lb weight (against gravity.. lifting) one foot of distance every second?

Housted wrote:
One horsepower equals 550 foot pounds (pound feet) per second.

In high school, in physics class, I generated 1 horsepower by running up a flight of stairs. :)

Housted

I'm NOT trying to start once again that infamous RV/truck owners' timeless discussion ... BUT: Isn't all horsepower the same? And also don't modern rotating machines merely convert their available horsepower into the required rotating torque at the required location using various gears and driveshafts?

Now here's what I'd sure like to have explained ... why a 300 horsepower diesel RV engine can "tow better" than a 300 hrosepower gas RV engine? That has never made sense to me. :h