# how power is measured in car? why rpm is specified?

1. ## how power is measured in car? why rpm is specified?

how power is measured in car? why rpm is specified?

there is big problem to compare the cars because of different rpm rates .
will you suggest me how power in cars are calculated?
i also found a bldc motor which power output is ~1900 watts. how can i count power at rpm?

•

2. ## Re: how power is measured in car? why rpm is specified?

Originally Posted by Vraj
how power is measured in car? why rpm is specified?

there is big problem to compare the cars because of different rpm rates .
will you suggest me how power in cars are calculated?
i also found a bldc motor which power output is ~1900 watts. how can i count power at rpm?
A car that uses some form of fuel (not electric) has an engine that produces varying amounts of horsepower depending on the RPM, the values quoted for a car are typically the maximum BHP (HP at the flywheel) at a the RPM which produces the maximum value. Rear wheel HP (just HP) is typically what you would see on a dynamometer.

Something like this http://www.edmunds.com/car-reviews/t...dyno-test.html

•

3. ## Re: how power is measured in car? why rpm is specified?

In case this becomes relevant, there is a parameter called torque, which is a different measure of engine power than hp output.

Maximum torque is not necessarily at maximum engine rpm, but in a lower rpm range. Acceleration is fastest at this rpm. It is the reason you start moving the vehicle in 1st gear, then shift to higher gears as the vehicle gains speed.

•

4. ## Re: how power is measured in car? why rpm is specified?

you need to compare horsepower not rpm - different cars and trucks use different combinations of high rpm, high compression, turbos etc to achieve as much horsepower as possible. One horsepower is equal to about 750 watts so you can look at it like an audio amp - you compare power in watts not voltage because manufacturers use different combinations of voltage and current to achieve the power out in watts.

- - - Updated - - -

Originally Posted by Vraj
how power is measured in car? why rpm is specified?

i also found a bldc motor which power output is ~1900 watts. how can i count power at rpm?
For the bldc I think that is power input - it will take 1900 watts from your power source before it burns up. Similar to a speaker is measured in watts - a 100 watt speaker will take 100 watts of power from an amplifier whatever the voltage or amps are - any more and it may burn up.

5. ## Re: how power is measured in car? why rpm is specified?

Horsepower is one thing (gives you have a high top speed) but torque is the real beast that breaks the tires loose and can make the care a tire smoking monster. Back in the old days '88 Performance Car magazine wrote an article on a car that was equipped with modifications that gave it what amounted to a torque mountain, which just so happened to sit right where the gearbox would put the next shift at. Needless to say the car could smoke the tires on a 4th-5th shift .
http://www.impactbumpers.com/forum/i...ow-dage-ds935/

That's why there's such a huge difference between driving a Honda S2000 (little torque, high RPM HP) and a ZR1 Corvette with 650 HP an 650 lbs/ft torque. You have to really work at it to make the Honda do burnouts, but the Corvette...better have a large tire purchase budget

--[[ ]]--