TORQUE AND HORSEPOWER : PERFORMANCE FACTORS NEEDED TO YOUR VEHICLE

         It's very important to know the performance of a vehicle because it shows that how efficiently it runs, how more it produces energy, how fast it transfers that energy. If the produced power is increased for the same vehicle after making changes in the exhaust system then it always indicates that there is a more chance of happening complete combustion. So going for obtaining more power always results in better fuel economy when initial conditions like the type of engine, type of fuel, power to weight ratio(the difference may occur since we are changing the exhaust system but that should be small), compression ratio etc are unaltered.But That doesn't mean that which vehicle has more HP, it will have better fuel economy.when the time of comparing the vehicle's performances, they should be identical in all the factors as I mentioned earlier then only more HP results in better fuel economy.That's why automotive engineers are always focussing on TORQUE AND HORSEPOWER @ SPEED when comes to performance.That means

             Maximum Torque @ Speed 

   Maximum HorsePower @ Speed 

         These two values are so important for any engine to know its performance. We can increase these values by making changes in the exhaust system. It leads to happen of complete combustion so that more power will be obtained with better fuel economy.We will discuss "what changes should we have to do in the exhaust system for obtaining better performance" in the next post.

       Many of us don't know the actual need of both the things. They both are needed for any engine, as more the values of those two, we can say "more performance that the engine has".

         Before discussing them, let's see some unit conversions so that we can easily understand.

• 1pound (lb) = 0.454kilogram (kg)(FPS -MKS)

• lbf = lb × g; kgf = kg× g = 9.807Newton(N)

• 1foot(ft) = 0.305metre(m) (FPS - MKS)

• lbf-ft / min  =  1.3578 kgf-m / min

          Let's understand the concept of each factor, how they are related, how they affect the performance.

1) TORQUE : 

        It defines that how much twisting force is acting at the crankshaft. It helps the vehicle to contact with the surface on which it lies for more time by providing good traction.More the value it is, more the traction will be. It also affects the developed power.

   Maximum Torque@Speed is important to determine the performance of an engine.

          It is also defined as the product of force and radius of the crankshaft.

Mathematically : 

            Torque = force× radius ( lbf-ft)
                        T = F×R (lbf-ft)
NOTE : 
      Mostly torque of any vehicle is expressed in N-m.Like Lamborghini Veneno Roadster has a maximum torque of 690N-m(507ft-lbf)@ 5500RPM.

2) HORSEPOWER: 
          It defines that how fast the produced energy is transmitted or work is done.Maximum Horsepower@speed is a very important factor to consider in order to determine the performance of an engine.HorsePower depends on both the SPEED and TORQUE.

                It is also defined as work done per revolution per time.
Mathematically :  
Power = (work is done / rev )÷(time)
Work done / rev = force×radius×2π (lbf-ft/revolution)
Therefore,
Power=force×radius×2π×N (lbf-ft/ min)
Here N= speed of crankshaft in RPM
Power = 2π×T ×N (lbf-ft/min)
In terms of Horsepower: 
  We know the general relation:-
         1HP = 33,000 lbf-ft / min
So, 1lbf-ft / min = (1÷33,000) HP
Therefore,
      POWER = (2π×N×T)×(1÷33,000) HP
                     = (T×N)÷(33,000 ÷ 2π)
                     = (NT)÷(5252) HP
That means
BRAKE HORSEPOWER=(NT)÷5252 HP
        Guys If you observe when the speed of the engine is equal to 5252RPM then from the above relation, we can say that HORSEPOWER is equal to TORQUE.When speed increases further, then Horsepower will also increase further.
Example: DODGE CHALLENGER SRT DEMON has a maximum power of 840hp @ 6300rpm.

NOTE :
•Don't confuse with the terms HP and BHP. Generally, HP is the power developed by the horse to lift the coal out of coal mine, invented by James Watt. 1HP = 33,000 lbf -ft/min
•BHP is the engine power measured at the flywheel without any attachments to the engine.It is expressed in HP.
•Wheel HorsePower is the actual power developed at the wheels after consideration of losses from transmission, accessories, bearings, and gears.Generally, it is the actual power we can find in any vehicle's specification. It is also expressed in HP.It is also named as simply Horsepower.
 • Mostly horsepower of any vehicle is expressed in HP(British or Mechanical or Imperial horsepower).But in some countries, it is expressed in PS, cv, hk, pk, ks or ch(Metric horsepower) because when expressed in PS, the value sounds better than the value when expressed in HP.That is why Lamborghini Veneno Roadster is advertised with 750cv(552kW)@8400rpm instead of 739hp@8400rpm.
               1 HP = 1.014 PS= 1.014cv
•With the confusion of expressing the power of an engine in different units, finally, all the countries have made a statement that it should also be expressed in the common unit "kW".
            1hp = 746watts = 0.746kW
            1cv  = 735watts = 0.735kW

TORQUE AND HORSEPOWER VS SPEED GRAPH

           In the above image, you can observe that the Torque curve is above the Horsepower curve before the speed of 5252RPM.That means the torque produced by the engine is more at low speeds, so due to fewer speeds(less than 5252RPM), horsepower produced is less than the torque produced by the engine.At the speed is 5252RPM, both curves intersect.Here torque developed by the engine is equal to horsepower.As speed increases further(greater than 5252RPM) horsepower is increasing further but the torque produced by the engine is decreased.

NOTE: 

           Remember that, as I said torque is more at low speeds but that doesn't mean that maximum torque is at low-speed value.It depends on various factors like degree of exhaust scavenging, stoichiometric ratio etc.For example, Lamborghini Veneno Roadster has a maximum torque of 690N-m(507ft-lbf)@ 5500RPM.Here maximum torque obtained after the speed of 5252RPM.

LET'S US GO WITH SOME EXAMPLES RELATED TO HP AND TORQUE: 
Example 1: 
      Let's us assume, a load of 500 lbf is to be lifted to a height of (2π× 1000)ft with the help of a rope connected to the flywheel of an engine.The radius of the flywheel is 1ft.
CASE 1: 
The engine is having a maximum torque of 500ft-lbf @ 1000RPM.  So, here to lift the load of 500lbf to a height of 2π×1000 ft, the engine will take 1min time. 
 HP of the engine = (T×N)÷5252 HP
                          = ( 500× 1000) ÷5252
                          = 95HP 
CASE 2: 
If the same engine is taken but it is having 500ft-lbf @2000 rpm then the engine will take only 30sec to lift the load.
              HP   =  95 ×2 = 190HP 
So, As HP of an engine increases, the time taken to do the work will decrease.
Example 2: 
 Taking the same conditions as stated above in example 1 but the engine is having a maximum torque of 250ft-lbf@2000RPM.Then the engine cannot lift the load actually since the torque produced is less than the load to be lifted (exactly half to the load value). So, in this case, by providing a gear exactly twice the diameter of the flywheel(transmission ratio is 2:1), we can get the reduced speed of 1000RPM with an increase in torque 500ft-lbf. So, the engine can lift the load of 500lbf.
Here HP = (500×1000)÷ 5252 
                 = 95 HP
Hence even though transmission ratios involved, the HORSEPOWER produced by any engine is constant.Only the difference occurs in the values of torque and speed.
Example 3: 
 Taking the same conditions as above stated in example 1 but the engine has to lift 100lbf load and the engine is having 100ft-lbf @ 6000rpm then  
 HP = (100×6000)÷5252
      = 114 HP ( compare with 190HP)
So, even though speeds are high, if the torque produced is small then Horsepower developed will be lesser.

FINALLY, WE CAN SAY THAT MORE THE HORSEPOWER THE ENGINE HAS, MORE WILL BE THE PERFORMANCE.
REAL LIFE EXAMPLES:
1) FOR TRUCKS: 
      N<5252RPM that means from the graph we can say that they have more TORQUE and less HORSEPOWER.
2)FOR SPORTS CARS:
       N>5252RPM that means, from the graph we can say that they have more HORSEPOWER and less TORQUE.