GarySargent

What is it and what difference does it make?

I hear a lot of people complaining about the lack of it.

zoom44

hi gary. let me first send you off to do some reading.
please read the following threads playing close attention to Rich's posts and the links he provides. they are very enlightening. then if you still have some questions post them back here and we'll see if we can answer them to your satisfaction

here

here

here

GarySargent

Hmm ok yes I admit I didn't search - doh!

Still don't really understand though despite reading all that and following the link to a discussion of torque at low revs and high revs (and lots of maths!).

Most of those threads were discussions about whether there is enough torque etc, but I still don't really understand what torque is (maybe once I understand those threads will make sense!).

I guess I don't particularly know what RPM is - other than more is better.

I can just about follow the stuff about fly weights etc but surely there must be some simple laymans way of describing rpm and torque in relation to cars?!

Whats the best way of comparing two cars? I keep seeing torque*rpm mentioned?...

zoom44

well rpm is simply revolutions per minute that the output shaft of the engine turns. torque is the power the engine makes. when you step on the accelerator pedal and you feel that push into your seat that is torque. and horsepower is the measure of that torque at any given rpm of out put shaft. now what is generally given by the car mags and such is peak torque and horsepower figures. but what is more important is the amount of power through out the rpm range. the question would be "how much of that power do i have available to me?" for instance because of it's high rpm ability the renesis is able to take advantage of gearing and and have something like 90% of its peak power available from @3500 rpm all the way to @8500 rpm. that is a very wide and flat power band and combined with it's light weight makes the rx-8 a very nice performing car. some other cars that have lower rpm limits but higher peak torque will actually be slower than the rx-8(even if they weigh the same) because the power will be trapped in a verry narrow rpm range.


now before i go on i would like wakeech, buger or rich to pipe in to let me know i haven't gone astray here somewhere and to double check what i have said and provide a graph if they would be so kind i'm off to tuck in.

GarySargent

Ah super this is all starting to make a lot more sense!

Yes a graph would be useful.

zoom44

here is a graph of the power curve of the renesis. notice how flat and broad it is? the are under the curve shows how much of the power you have available throughout the rpm range.

mhopley

Well Gary it looks looks like you know a lot more about Tivo's than cars
Only joking - glad to see you have ordered your RX-8 and apprecriate your work on tivocommunity.

Mark

GarySargent

LOL Well I know the RX8 looks fantastic and will be much more powerful than my existing car so thats all I really need to know!

Even without knowing what torque is I think I've managed to order a reasonably good car :D

wakeech

everything looks good so far zoom.

you asked "what is torque"?? it's a rotational force. what difference does it make?? force is what accelerates your car. why does power then matter?? because, my friend, torque measured at the business end of the engine (that's the flywheel: where the clutch grabs onto the engine to spin the wheels) means nothing without consideration of the gearing: force at the flywheel does not equate in any fashion to force at the ground, where the pushing occurs.

horsepower brings rpm into the equation, which as zoom said, is how fast your engine is spinning, and like you said: the faster the better.

if you can make a tiny bit of torque (force) at a very high rate of speed (like the RENESIS does), you end up with a lot of power: using gears, we can multiply the force of the engine as we devide the speed it is delivered at, meaning the power through to the wheels stays the same (if there were no such thing as frictional losses, and other things like that), but the force at the wheels will increase. so, you CAN have a tiny motor, with the right gearing and enough rpm and breathing (which is the tricky bit) pull a car as hard as one with a bigger engine which makes the same level of power.

zoom44

so now that wakeech has mentioned gearing and it's effect on drive-wheel power here is a post from buger that may help explain just how that rx-8 with the "low" torque peak number can performs as well as it does. low weight + high rpm + gearing

for more info on this topic it would be much easier for you to read what has already been written in the original thread here. i am starting you on page 4 but feel free to start at the beginnning if you feel the need.

rael

Gary,

The childish way I understand it is as followss; It is the kick in the back as you put your foot down. In my TT it last a relatively short time before the charge stops as I run out of revs, have to change up the get that kick again. In the 8 there is no kick, the acceleration is more flat. Both cars get to the same place at roughly the same time with the TT having better initial take-off but the 8 catching up and eventualy overtaking before 60mph is reached.

This was one of the earliest questions I asked and at the time buger was kind enough to post some comparison graphs which must be around somewhere. Anyway, point is, that you will not get that head snapping feeling in the 8 but instead a gradual linear build up of speed.

rael