understanding max torque and power

[rithu09in]

Hi Team,

 

  I would like to understand what is max torque and power that Car companies specify in technical specs... It would be something like the foll

Max. Horsepower (ps/rpm)

94/5500

Max. Torque (kg m/rpm)

12.5/3500

 

I understand that these numbers are w.r.t to RPM's... what does this indicate?

 

Is it that the car which gives you max power and torque in lower RPM's is better or is it vice versa ?

 

 

[designersf]

Peak power is generally made at a higher RPM and peak torque at around 2/3rd of max RPM.

Power increases till max rpm reached while peak torque comes at a lower rpm and ofter that it decreases

Pls correct me if im wrong

[designersf]

but the features varies from engine to engine and from tuning to tuning

[rithu09in]

So... is it that this car reaches at its max speed at 5500rpm?

[sgiitk]

If you forget the constants the power is just torque multiplied by the rpm.

Power = constant * torque * rpm

This is the reason why peak power is at a higher speed than peak torque.

In general for best results you should try and keep the rpm between (just blelow) peak torque and (just beyond) peak power. This is why you have a rev counter in most cars today.

[rithu09in]

sorry.. i did not understand what a rev counter is.

[darklord]

http://www.cpamis.com/images/Speedometer.jpg

Check the above picture, the dial on the left is the rev counter. Since it is "x1000" it would show the RPM in thousands.

@moderators

I'm not able to use the image option, it shows "Only members with sufficient permission can access this page"

[sudeepd]

Power increases till max rpm reached.

Max Power comes at some rpm less than Max RPM.

Example-

In Tata Indigo XL's Owner's Manual, it is given that "Max Power is 70Ps at 4000 RPM as per DIN 70020", "Max Torque is 140Nm at 1800-3000rpm as per DIN 70020".

 

The Engine of Tata Indigo XL can be revolved upto more than 4000 rpm (around 4500-5000rpm).

So Max Power is obtained below Max RPM.

[sudeepd]

In general for best results you should try and keep the rpm between (just below) peak torque and (just beyond) peak power.

SG, you are making mistake. I think you want to say try and keep the rpm between (just above) peak torque and (just below) peak power.

[sgiitk]

We are both correct. You for racing (you may still want to hit peak power), me for normal driving!

sgiitk2008-08-07 18:04:02

[sgiitk]

Max Power comes at some rpm less than Max RPM.

.......

So Max Power is obtained below Max RPM.

This is normal. Max rpm is the limit to which the engine can be taken to without damage.

The torque drops off rapidly as you near the peak rpm. The power (rpm*torque)  follows suit. So the peak power is invariably somewhere below max. rpm. Revving beyond this limit may damage the engine. Modern EMUs do not allow you to over-rev.

sgiitk2008-08-07 18:08:42

[anjan_c2007]

Torque is defined as the quantum of rotational force derived from rotational movement, if my memory of physics serves me right. Its measured in Newton meters (Nm) or Kgm.

[opendro]

If you forget the constants the power is just torque multiplied by the rpm.

Power = constant * torque * rpm

This is the reason why peak power is at a higher speed than peak torque.

In general for best results you should try and keep the rpm between (just blelow) peak torque and (just beyond) peak power. This is why you have a rev counter in most cars today.

A very good answer, exactly. From the above formula, many might be wondering if increasing the rpm would simply increase the power. And many do believe in that and throttle fully without realizing that it does not really help, because the torque suddenly dips beyond certain rpm, resulting in lower power.

[heavygear]

why torque drops when the engine is approaching the peak rpm? whats the mechanism?