Hello everyone!
Here i am again with my stupid questions! I was thinking about the power of an engine and i just wondering if there`s any relation about power and speed! I mean, for example the A12 engine has less power that the A15, does this mean that the speed is less to, or isn`t proporcional? Can someone inform me about this?
Thanks

Power is just a measure of work.

However, it takes a certain amount of power to push a particular car through the air due to aerodyamics, and friction of the tires agains the road. For a Datsun 1200 coupe or sedan, it takes about 35 rear-wheel-horsepower to push the car along at 90mph (140 kph).

To go faster you need more horsepower.

For more details, see wiki - Performance

thanks dd! always with the answer in the tip os the tongue...
cheers

I'll throw in another wrinkle. With light cars we often speak of power to weight which does great things for acceleration but at some point it takes "power" to push the car through the wind, so taking out 100lbs will likely not give the same result in speed as adding power.

Tom

I was thinking of this one if you boys can help?, (power Vs Speed) A V8 engine has power to pull loads like towing a trailer or caravan, even a car full of people with next to no trouble.
But!!
Then you have a rotary engine rev's like there is no tomorrow and can run some quick times on the drag strip, but cant carry any loads. No good for towing or carrying lots of people. i have heard of rotary engines blowing up when trying to pull a trailer load, espically up hills.
Im sure its not rocket science, but since we are on the topic i find it interesting.

Its really all about torque isnt it?

Power is a representation of torque at a certain rpm. Rotarys make all their power really high in the rev range and have nothing down low, while v8's have big torque down low too. So say it takes 200 hp to tow a boat up a hill at 60kph, a v8 can do it at 2500rpm while a rotary will be doing it at 7000.

cheers

a rotary will struggle to get the boat moving at all because they don't have the torque down low where its needed most when moving heavy things.

torque is the turning force an engine produces. and when it comes to moving heavy things from a standstill, sheer brute force wins everytime. AND you need access to it at low rpm so you can make it move in the first place.

horsepower means very little for tow cars - a 240bhp S2000 will suck at towing compared to a 120bhp diesel Patrol.

Ianey has it, horsepower is only a measure of how high up the rev range that engine makes torque.

That feeling of being pinned into the back of your seat, thats torque, the ability to spin the wheels, thats torque, to do 0-100 in 5 secs, thats torque.

Power is just an abstract term for making torque high up the rev range.....funny enough top speed is about how long you can hang onto your torque up the rev range.

Race cars aim for torque at the end of the rev range to guarantee they have torque at the vehicles tops speed.

So power tells you a little about how much torque is made and a little about where it is made in the rev range.

If you want to win a horsepower challenge, particularly in a turbo just delay the boost as long as possible and get the engine to rev as high as you can on full torque....undrivable but guaranteed to get you the slab of Jimmys at the horesepower heros day.

Im convinced Some great info there

Go the horesepower heros !!!

Kind of sad that a stock A15's peak torque is low (at 3200rpm). But, what the hell, we gain fuel economy instead...

Compared to new cars, where u gotta rev up to 4k++ rpm before shifting to 4th or 5th gear, a15 just need to be revved up to 2.5k...or perhaps 2k...and the engine will have enough torque to pull the car on the following gear.