Page 18 - PCA Metro NY Region POST | 2019 July eMag
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NOTE TO READ- ERS: This article discusses technical issues about engines and transmissions.
It is not about track- oriented driving.
Torque and Horse- power
You own a Porsche. You love it dearly since it is worthy of that love and it is truly a work
of art and high perfor- mance. Maybe you take it to the track, maybe it’s your daily driver, or maybe you just show it off on
Northern Boulevard, but you certainly want to be able to hold up your end of the conversation at the watering hole.
The terms ‘torque’ and ‘horsepower’ get tossed around quite a bit, but they are often misunder- stood. In this article, I will try to explain them. In the simplest terms, torque is a force, while horsepower is force over time.
Torque is a twisting force, like what you apply
to a wrench when you tighten or loosen your wheel lug nuts. It is measured in foot-pounds. If you have a wrench which is one foot long at- tached to a nut, and on the other end you place a 10-pound weight, you are exerting a torque of 10 foot-pounds. If you replace the 1-foot long wrench with a 2-foot long wrench and the same 10-pound weight, you will have a force of 20 foot-pounds. This is the principle behind a break- er-bar: the longer the bar, the greater the torque for the same applied force.
Torque can be multiplied as above, which is also what gears do. The engine in your car is apply-
ing torque to the flywheel. That torque goes into the transmission, where it is channeled through a series of gears and it is transformed at the other end into a different amount of torque (and speed) which depends upon the gear you have chosen to engage. The simplest way to visualize this is to consider a multi-speed bicycle with a derailleur system. Connected to the pedal are 2 chainrings, as the front set of gears are called in bicycle terminology. Let’s say that the larger chainring has 30 teeth around its circumference, while the smaller one has 20. Let’s say there are also 2 gears in the rear gearset, with teeth per gear of 20 and 10. If you select the larger gear (CASE A) in the front [with 30 teeth] and the smaller gear in the rear [with 10 teeth], each revolution of your feet will cause 3 revolutions of the rear wheel [30 divided by 10], but if you select the smaller gear (CASE B) in the front (with 20 teeth) and the larger gear in the rear [with 20 teeth], each revo- lution of your feet will cause only 1 revolution of the rear wheel [20 divided by 20]. You will have 3 times as much torque in Case B as in Case A.
The above explains why a car can start up a hill easily in 1st gear, but not at all in 5th gear. The underlying torque (twisting force) of the ‘engine’ (your feet on the bicycle and the engine in the car) is being multiplied more in the lower gear than in the higher one, just as in the use of the breaker bar, to overcome the downward force of gravity due to the hill.
Next, let’s consider the internal combustion en- gine in its simplest case – a 1-cylinder, 2-stroke engine. Each time the piston approaches the top of its stroke, the spark plug fires, setting off a mini-explosion creating an enormous pressure in the cylinder, which pushes the piston down.
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Track Ramblings

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