Today I talk about the difference between horsepower and torque.
I go over the differences between the two, and how they are related.
To understand foot pounds of torque, imagine you are trying to get a rusty bolt off.  You weight 200 pounds, and have a ratchet with a one foot long handle.  If you are putting your entire weight onto the handle, you have 200 ft-lbs of torque.  If you put a two and a half foot piece of pipe over the ratchet, you now have 500 ft-lbs of torque.
Horsepower was defined by James Watt as 33,000 ft-lbs per minute or 550 ft-lbs per second.  What that means is that in the second example with you generating 500 ft-lbs, you were making about 1 horsepower, however briefly until either you fell off the ratchet/pipe combo or ran out of room for it to move.  That would explain why you wouldn't be able to move the car very fast or very far.
There is a relationship between horsepower and torque.  The relationship is horsepower = (torque x RPM)/5252.  So to get the horsepower for an engine, you multiply the torque it is producing by the rpm it is running at and divide it by 5252, which is a constant.  So it stands to reason that the faster you can spin an engine, the more horsepower it will produce.  That usually means less torque (and by extension horsepower) at lower RPM due to the compromises needed to increase high RPM power.
The key to remember is that we are talking about horsepower and torque at the crankshaft, not at the wheels.  Taking gearing into account greatly changes the horsepower vs torque thought process.  If you have an engine with a lot of horsepower and little torque, so usually a smaller engine with its power high in the RPM range, you can use lower gearing to increase the torque.  So if at X RPM the engine is making 400 ft-lbs of torque, and first gear in the transmission is 2.5:1 and the differential gearing is 4.0:1, the torque is multiplied ten times.  So that 400 ft-lbs becomes 4000.  But if we have an engine that is making 200 ft-lbs at 2X RPM, and the transmission gearing is 3.40 and the differential gearing is 5.88, we are a rounding error away from multiplying that 200 ft-lbs by 20 and getting the same 4000 ft-lbs at the wheels.
Yes I know that the numbers are convenient, that is why I picked them.  But the point is, that you need to be looking at the torque vs horsepower at the wheels as well, not just at the engine.
So we know we can increase torque with gearing, but what about the horsepower part of horsepower vs torque?  Since the torque is multiplied by ten, but the RPMs have been divided by ten, the horsepower is the same.
With the gearing, that is the reason that new vehicles come with 5+ speed transmissions, especially the automatics.  It allows the engine to operate at the best RPM for acceleration (and fuel economy).  With more gears, you can do more with less, since the RPM drops between the gears isn't as great.
So to show how it all works together, let's compare two engines with the same horsepower, but very different torque
First, lets start with a 400 HP 318 Mopar.  Yes, you can get 400 HP out of a 318, check here for the details.
And subject number two is a 6.7 liter Powerstroke diesel from a Ford truck.
For some of the basic specs, the 318 makes 400 HP at 6,200 RPM, and the Powerstroke makes 400 HP at 2,800 RPM.  For torque, the 318 makes 382 lb-ft at 4,900 and the diesel cranks out 800 lb-ft at 1,600 RPM.
Lets assume that both vehicles weigh the same, and have the same transmission.  This mythical magical car will only differ in the engine installed, and the rear end gears.
Lets assume that they have an eight speed transmission, since this car will have the latest and greatest set up.  The main reason is that the close gear ratios make the comparison easier.
Regardless of gearing, the horsepower to the rear wheels doesn't change.  Let's ignore friction losses, and since this is a magic car anyway, let's say they both have 400 HP at the rear wheels.  The reason that