So what is it that is actually "revolving"? What are RPMs? It is the rotations per minute of the crankshaft.

Most cars have a dial that shows the RPMs or revolutions per minute also known as "revs." This dial is called a tachometer or "tack" (pronounced "tack"). The numbers on the dial are in thousands of revolutions per minute.

The "tack" in most cars when they are coasting in gear should sit at around two and a half to three on the dial. This will get the best miles per gallon out of your car and result in the least wear and tear on the engine. Consistently driven at higher "revs" your car will start to guzzle gas. You should shift up from one gear to-the next when the-"tach" hits about three and a half on the dial. And shift down to the next lower gear when the "tach" goes much below two and a half.

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Do not push the "revs" above the red line marked on the tachometer. If you go over the maximum level of RPMs that is safe for your car as shown by the red line the engine valves will be permanently damaged. The engine will "fire" while the valves are still open and the car will backfire. For normal driving purposes you do not need to get anywhere near the red line on the dial, even when accelerating or overtaking.

With the car parked and the engine running, lift up the hood of your car, and leave the car door open. Put your foot on the accelerator with the hand brake on and the car out of gear. Gently increase the pressure on the gas pedal. Listen to the engine. Do you hear the increase in revs? Don't rev it too high!

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