What does rpm means for a car?

Question

Different cars have different rpms. What do they mean? The higher the better or?

Answer 1

Revolutions Per Minute is the short answer. As with most things, the more you look into it, however, the more there is to see. In this case, you may be interested to know what happens in each "revolution" which refers to one full rotation of the crankshaft in a piston engine, or a rotary engine, and to one full rotation of the turbine is a jet engine, which has no crank shaft.

Since the odds favor you being in possession of one or more piston engines in your car, motorcycle, lawnmower, chain saw, or gas powered leaf blower let's stick to that.

Basically these can be divided into two-stroke and four-stroke engines and the difference determines what is happening in each revolution.

Let's take a typical four-stroke engine first, as you will find in most cars, regardless of whether they are three, four, five, six, eight, ten or twelve cylinders. In each case there are four distinct operations that are being performed and they are divided up into two operations per revolution of the crank shaft. If you think about it a bit, it will be intuitively obvious why, but if I am to earn two points, I supose I should explain it.

You know that the way the engine works is that a mixture of fuel and air is sent to each cylinder where it is ignited by a spark plug, or similar device (diesel engines use glow plugs for example). In a four stroke engine, first the fuel/air mix is sprayed in the cylinder as the piston goes down, creating a suction within the cylinder--this is called the intake stroke. As the piston is connected to the crank shaft via what is called (so cleverly) a connecting rod, it necessarily is turning the crank shaft half way round as it does. (Think of each piston/connecting rod assembly as a hand on a crank handle and the crank shaft (also so cleverly named) as being a series of crank handles all connected in a line to form one long shaft to which each of these "hands" may grip to turn it in unison.)

So the crank is turned half way round and now it is on its way back up. Your valves which let in the fuel/air mix and let out the exhaust are now both closed. to seal off the cylinder so that the piston may trap and compress the fuel/air mix as it rises. This is the compression stroke, and the crank has now completed one full revolution--and note, without producing any power so far in this cylinder.

Now the spark plug fires the compressed mix, thrusting the piston down ahead of the explosion and in the process giving the crank shaft a mighty powerful turn (the big dog's hand on the ice cream freezer). This is then called the power stroke, and once again the crank shaft has turned half way round.

Now the piston is ready to come back up and push the exhaust out, and your exhaust valve opens to permit this--hence the name, the exhaust stroke--and once again the crank has turned half way round.

Once this is done, the intake valve opens again as the piston goes down and fuel/air mix is drawn in again--another intake stroke--and the whole process repeats itself over and over in each cylinder.

So in a four stroke engine, as you can see, each cylinder produces power once every other revolution of the crank shaft.

Without going into similar detail, a two-stroke engine combines these functions so that the piston fires on each revolution.

Answer 2

They are right, it is revolutions per minute. However, it is not as if every car has one RPM it is set to. Basically, the farther you push the accelerator (gas pedal) the higher your RPMs will go. You can read your current RPM by looking at the tachometer on your dashboard, which is obvious because it says RPMs on it. Most will also say "x1000" to indicate that the single digit number you see is not in fact the number of RPMs but 1/1000 of it.
The point at which the increase in RPMs will start damaging your engine is called the "Red Line" and is marked on your tachometer by the lines getting red (no one said this was rocket science). Most normal cars red line around 6000 or so, but some sports cars get as high as 8000. More RPMs means more speed, and red lining later means you can stay in lower, more powerful gears longer, which allows for greater acceleration. RPMs aren't the only variable that increases power, and the size of the piston is very important for amount of power.
Neither lower or higher RPMs are necessarily better. In fact, if you are trying to get power out of your car you may need to push to a higher RPM. High performance cars can reach very high RPMs, and sport motorcycles can go even higher. When you hear an engine, the higher in pitch the sound is the more RPMs it is operating at. The problem is that usually the more RPMs, the more gas that is being consumed, and nowadays that's something to be concerned with. Also, if you want to tow something you want a bigger engine, which will probably use fewer RPMs with larger pistons.
I hope this helps (it may have been overkill...)

Answer 3

Stands for Revolutions Per Minute. When the engine crankshaft turns 360 degrees it is one Revolution. The number of times the engine does this in a minute is the RPM it is set to.

Check: http://en.wikipedia.org/wiki/Rpm

Answer 4

RPM stands for revolutions per minute

Answer 5

rpm of course means revolutions per minute.it just depends on wat u need the motor 2 do racing engines are made 2 run at higher rpm 4 power and performance.those hi rs are hard on an engine and arent needed for avg driving.also engines desinged to operate at lower rpms generally get better milage and run smoother and quieter

Answer 6

RPM = revolutions per minute

Answer 7

RPM means Real Posh Motor!

The more rpm`s, the posher it gets!

Answer 8

RPM is how fast the motor turns.. or is able to rotate the crank shaft inside the motor...

Answer 9

rpm is revs per minuete thhe more revolutions the faster your speed

Answer 10

This is how many revolutions per minute the engine runs.