Learning

Home  \  Repairs & Maintenance  \  Learning

Hello,
I am a 13 year old and am interested in auto mechanics. I know a little about cars(probably more then most people my age). I would appreciate it if anybody could help point me in the right direction. Any websites or books for people my age?(so i can understand it) Thanks for all the help.
-kaz

posted by  kaz_

howstuffworks.com

has a whole section on automotive related items, would be a good idea to know how most of the components on a car work before getting into the deep stuff.

posted by  speedy266

I'm confused about rpm, torque, and horsepower, and how they all compare. The horsepower curve really confused me. Can someone try to help me understand this?

posted by  kaz_

Well im not really an expert on Hp, Torqe and rpm's but heres what i know, HP is the Power in how many horeses it would take to get the same affect, RPM's are the rotiations per min of the cam shaft (not the tires) and Tourqe is how much the egine is able to put down the drive shaft, through the tires and onto the ground.. (if anyof this is wrong then let me know)

83camaro

posted by  83camaro

yea ok, i got that, but...i got sooo many questions. OK..

-what's the difference between horsepower and torque? and how do rpms affect them?

-From my understanding, with a manual trasmission car you turn the car on(it will be in park), then you disengage the clutch switch to 1st gear, (at this point the car is running at a certain rpm right?) so you engage the clutch and the car starts moving, slowly? If im wrong can you please explain it to me (the clutch). I searched google but it's just really confusing.

OK, so maybe not a lot of questions but some time consuming ones.

posted by  kaz_

As the RPM's go up, the HP that the egine generates goes up, until it hits the Maximum HP at the Maximum RPM that the engine can handle before blowing up, ie 300hp@7500 rpm (if anybody sees that this is wrong pipe in, because this is how i understand it.) Not quite sure how/where the torque is generated so if some one can fill us both in on that it would be great

83camaro

posted by  83camaro

yea, got yea. torque just totally throws me off, what's the difference between it and HP?

posted by  kaz_

Torque is how much force the engine is putting out over the band, horsepower is derived from torque but is with respect to time.

Torque = Force * Perpendicular Distance
Horsepower = torque * revs/minute * 1/5252

posted by  speedy266

kaz_ seeing as you are just 13 this may help.

In the context of cars we generally only talk of torque in terms on circular motion. This makes the calculation of torque failry simple. Speed 266 has given you a formula that you can use. The metric equivalent is NM = kW x 9551 /rpm.

There is always big debates about torque and power in car forums, as if they are mutually exclusive. None of them ever seem to think outside the square and see how futile the arguments are.

So lets say you can use google and work out the difference between force, work and power. They are fairly simple arithmetic equations.

In simple terms force is a push or pulling action and is measured in pounds or newtons. I'll stick to metric from here on in because its simpler.

Work is force applied through a distance and is measured in joules. A joule of work is achieved when you apply one newton through a distance of one metre.

Power is work over time. A watt is simply one joule of work over one second. 746 watts = 1 horsepower.

So where does torque come into it? Well torque is not a base unit. Without any energy there will be no work, because work is the transfer of energy. Without work there will be no power and logically without power there will be no torque.

The stuff we put in the fuel tank is what we need to get the engine going, it has potentional energy just wanting to do some work, in fact it is rated by supplier in megajoules/litre (about 36.656 megajoules to be more precise). There is no reference to torque in the literature, but we know if we burn it all in a certain time how much power we are going to get. The reason you can't simply work out a torque value from the fuel characteristics, like you can with power, is because it varies with the engine that's burning it and who's to say the liberated energy is going to be used to rotate some gears and wheels anyway.

Ok torque, well you can call it anything you like, e.g. twisting force, but it's simply force x moment arm. Don't let it get to you now, you have a bit of time on your side to learn about moments. Now look at this equation:

Torque (NM) = watts/(2Pi x rps)

rps = revolutions per second.

As soon as you see Pi you just know we are dealing with someting round, in this case rotational motion. And that is what an engine, gearbox and wheels are in business of. They are a means of transferring work produced by the fuel burning at a certain rate to the road to deliver force. And the rate the work is transferred is governed by the power produced. Torque does not produce anything in this situation, it is a product of power applied in a circular or annular fashion.

The amount of torque measured is dependent on the amount of force and the magnitude of the moment arm and it's this moment arm (leverage) that the internet experts seem to forget when they have circular arguments about torque and power.


Because dynamometers generally use a torque meter of some kind to measure an engine's performance, the operator or computer simply rearranges the formula to get the power reading: watts = NM x 2Pi x rps or hp = ftlbs x rpm/5252

.

posted by  Wally

very well put, what site ya get that off of?

posted by  Jediah

ah, so i see

posted by  Jediah

Some of us have been around long enough not to refer to the internet for year 9 physics :wink2: I suggested google because I'm sure there are plenty of sites that explain it a lot better than I have.

posted by  Wally

a simple way to think about the difference between torque and horse power is this: torque gets you going and horse power keeps you going...the feeling you get when you hit the throttle and you get pressed against the seat is torque. the looks you get when you pass 120 mph is horsepower. horse power is the result of torque

posted by  LCRedneck

I guess it doesn't matter how people think about these things, it's not going cause a planetary shift and the people who need to know won't be consulting auto forums thankfully. :confused: .

posted by  Wally

Your Message