Horsepower....what the heck does it mean?

[MaxPete]

Howdy all!

Being a huge fan of history, I was delighted this morning when one of my favourite YouTubers - The History Guy (or THG as he is popularly known) posted a video on that familiar measure of engine output the “horsepower”.

We all use the term (and many people use it correctly too), but how many folks know what it actually means and from where it came? Have a gander at this video and find out!

The only quibble I have with the video is that about halfway through, THG switches from the correct pronunciation of the name of the inventor of the steam engine: Newcomen (with an “N” as the last letter) to “Newcomer” - with an “R”.

I guess he is getting tired of being inside his house so much and is getting a bit stale (who isn’t?).

Aside from his odd inability to pronounce certain military ranks correctly (he persists in saying “Loo-tenet” rather than “Left-tenant” when discussing British and Commonwealth officers) I think that THG does a incredibly good and well-balanced job of describing some of the most interesting and occasionally obscure aspects of the history of the world.

Highly recommended!

Pete

 

[Pipes]

That's pretty cool....I cannot remember where I heard it but the saying goes 'Torque gets you going,Horsepower keeps you going'...

 

[Jim]

"In all things in life, there's nothing more foolish than inventing." James Watt.
Consider Edwin Armstrong, the inventor of the FM radio. He spent the rest of his life fighting in court for his due. In 1954, practically broke, he killed himself.

 

[bosco659]

Great video Pete. Watched another on the Phillips vs Robertson screw. Will have to watch other in his series. Thx for the heads up!

 

[MaxPete]

That's pretty cool....I cannot remember where I heard it but the saying goes 'Torque gets you going,Horsepower keeps you going'...

....or as car salesmen say, "People buy horsepower, but they drive torque".

Most people would be unimpressed by the HP ratings of large diesel pickup trucks - that is why the OEMs advertise torque ratings for these vehicles. The thing is that HP = Torque x RPM with some fudge factors thrown in to get the units to work out.

So - the torque rating of a big 6.7 litre Cummins diesel in a Dodge pickup is 1000 ft-lbs and 400 HP - but that is likely at an engine speed of around 2500-3000 RPM or so.

At 2500 RPM, more motorcycles would be hard-pressed to get out of their own way (or as Marlon Slack says - "they couldn't pull a fat kid across a wet linoleum floor") - but at 2500 RPM your average diesel engine is maxed-out and pulling like a banshee.

So - you can have a relatively small HP rating and huge torque rating - at low RPM (such as in a steam engine or a big diesel) or you can have a high HP rating and low torque - at a very high RPM - such as in a motorcycle engine which can turn at 8-14,000 RPM.

The History Guy has videos on a huge range of topics from technology, to interesting personalities in the history of many many different countries. His work on US presidents is particularly interesting - and I suspect it will become even more interesting sometime soon....

I just wish he would learn to pronounce "Lieutenant" correctly....

 

[member28833]

Think XS650 vs RD400.
Don't think so many guys are too impressed with the 50 horse power of the XS. Its the smooth torque.

 

[Jim]

Horsepower is actually the more important figure if you want speed. That's why the good Mr. Watt put the time factor "per minute" into his equation. Torque is the amount of force that can be exerted... horsepower is how fast you can put that down on the road. Consider 2 engines... one with 100hp and 100 ft lbs of torque, and the second with 200hp and 100 ft lbs of torque. Both can exert an equal amount of force, the second can do it twice as fast.
Zoom zoom....

 

[MacMcMacmac]

Just don't use "torques" to describe lb/ft. It drives me up the wall.

Smokey Yunick said the vast amount of drivers would be best served by a high torque 4 cylinder motor. The proliferation of 2.0t automobiles would suggest he was correct. It certainly makes more sense than driving a 3 ton station wagon with a 455 Olds to pick up the groceries did.

 

[MaxPete]

Yup - and the other thing is units.

I have seen people quote torque in PSI (pounds / sq. inch) which is a unit of pressure and not torque or simply in "pounds" which is a unit of force while others even quote torque in unknown units like ft/lb - which would be "feet divided by pounds" - which also has nothing to do with torque. The term ft/lb is sometimes used in engineering for uniformly distributed loads such as snow on a roof or something like that - but it ain't torque.

The most common units of torque in the Imperial system and the SI or metric system are:

• ft-lbs (one pound of force acting at a distance of one foot);
• in-lbs (one pound of force acting at a distance of one inch);
  
• N-m (or Newton-meter which is one Newton of force acting at a distance of one meter).

The "distance" is often referred to as the "arm" and the Newton is an SI or metric unit of force which equals the force required to give a mass of one kilogram and acceleration of one meter per second**squared or one meter per second per second if you like.

Does everyone's head hurt now?

 

[MaxPete]

Think XS650 vs RD400.
Don't think so many guys are too impressed with the 50 horse power of the XS. Its the smooth torque.

...at relatively low RPM. I could be wrong, but I'd bet that something like a Honda CB750 would develop 50 HP only an an RPM of 7-9,000 whereas an XS650 produces that torque at a much more sedate 5,000 RPM.

 

[Mikey]

Yup - and the other thing is units.

I have seen people quote torque in PSI (pounds / sq. inch) which is a unit of pressure and not torque or simply in "pounds" which is a unit of force while others even quote torque in unknown units like ft/lb - which would be "feet divided by pounds" - which also has nothing to do with torque. The term ft/lb is sometimes used in engineering for uniformly distributed loads such as snow on a roof or something like that - but it ain't torque.

The most common units of torque in the Imperial system and the SI or metric system are:

• ft-lbs (one pound of force acting at a distance of one foot);
• in-lbs (one pound of force acting at a distance of one inch);
  
• N-m (or Newton-meter which is one Newton of force acting at a distance of one meter).

The "distance" is often referred to as the "arm" and the Newton is an SI or metric unit of force which equals the force required to give a mass of one kilogram and acceleration of one meter per second**squared or one meter per second per second if you like.

Does everyone's head hurt now?

 

[Mikey]