HOW TO INCREASE HORSEPOWER ? CAN WE GET BETTER PERFORMANCE BY MAKING CHANGES IN EXHAUST SYSTEM ?

       To increase HORSEPOWER, the main factor we have to minimize is Back Pressure.

• What Is Back Pressure?

           The pressure which restricts the flow of exhaust is called exhaust Back Pressure. Since it is named as back pressure, it is also called as Negative pressure because it opposes the flow of exhaust.
     For example, if the atmospheric pressure is 5 times than the normal pressure that is 5atm then the atmospheric gases surround the exhaust tip will be forced to enter the exhaust pipe results in oppose the exhaust flow coming from the pipe.This is called back pressure.Another way of happening back pressure  is when there is restriction in the exhaust system.Due to oppose of exhaust flow, back pressure waves will be created.

• Causes Of Back Pressure :

1) Atmosphere.
2) Restrictions in exhaust system like mufflers, resonators, catalytic converters, turbochargers, filters etc.

• How Much Value Should It Be?

       Mostly, people would think that there should be a minimum value of back pressure in their exhaust systems.We have come across so many statements from people saying that "back pressure is needed provided the value is less".Wait! That is wrong.They were confused with the concept of exhaust velocity.Ya, you heard me right.What they wanted to actually tell us is, the value of exhaust velocity should be a limited value.That is, it shouldn't be either a minimum or a maximum value.It should be in between those values.Meaning, if the exhaust velocity is too low by providing a big exhaust pipe then there will be a slow flow of exhaust.This may increase back pressure.Similarly, if the exhaust velocity is too high by providing a very small diameter of pipe then there will be increase in restriction of exhaust gases when their amount is too more.This also leads to increase in back pressure.So there should be a ideal value of velocity so that no restriction to exhaust gases.So proper selection of exhaust pipe diameter with tip  is very important.The above discussiin is all about how the exhaust velocity effects the back pressure.Hence, the back pressure  value should always be as less as possible.But the exhaust velocity should be a ideal value.

• Let us see some cases:

1. Less Back Pressure : 

        Obtained by: using highly tuned exhaust system (by using Vortex mufflers or Corsa RSC mufflers).

       Causes: an easy flow of exhaust gases.Almost no restriction.It leads to a very high performance.

2.Minimum Back Pressure: 

       Obtained by: having less restrictions like a single mufler or resonator or even a  curved/bend pipe in the exhaust system.

           Causes:  the exhaust flow is restricted but which is comparitively less than the exhaust restriction in the case of high back pressure.

3.Maximum or High Back Pressure : 

         Obtained by: Restrictions in EXHAUST SYSTEM like mufflers, resonators, catalytic converters, turbochargers, filters etc.

           Causes: less chance of flowing more exhaust gases to outside so that force required by the piston to do the work on the exhaust gases to expel them is more results less Horsepower.

Methods to reduce Back Pressure so that Horse Power will increase : 

1. REMOVE RESTRICTIONS:

       Basically, restrictions in the exhaust system hamper performance.For getting better Horse Power, major criteria is to remove all restrictions in the exhaust system.Restrictions in the exhaust system are mufflers, resonators, catalytic converters, turbochargers, filters etc.

2. EXHAUST SCAVENGING : 

            Definition: The process of Removal of all combusted gases from the cylinder and there is no gases present inside the cylinder in order to react with newly entered fresh air-fuel mixture.

      So by following exhaust scavenging, we will increase the HorsePower.

           Generally, exhaust gases are traveling in the form of exhaust pulses.Exhaust pulses mean they constitute low, medium and high-pressure waves. Suppose exhaust gases are expelling out from the cylinder and traveling from left to right. Always exhaust pulses comprises LMH ( Low, Medium, High ) pressure waves from left to right. So, Normally these Low-pressure waves in the exhaust pulses help to expel the gases out from the cylinder by traveling gas due to the difference in the pressure of High-pressure wave in one exhaust pulse to the Low-pressure wave in consecutive exhaust pulse.But this process does not lead to exhaust Scavenging. 

          For obtaining exhaust scavenging, we need Generally tuned exhaust. That means the low-pressure wave exactly occur at the exhaust valve when it is open.Due to this, easy flow of exhaust gases will take place.So either in a single cylinder or multi-cylinder engine, tuning the exhaust system will improve the degree of exhaust scavenging.

         Let's see how scavenging exactly takes place : 

      • In case of multi-cylinder engines:
                          exhaust manifold has parallel pipes which are merged into a single pipe. At the area changing, due to the sudden expansion of area causes a low-pressure wave ( built up by the colliding of pressure waves), which acts at the exhaust valve exactly when it opens. So, easy flow of gases will take place. Here the timing of exact occurrence of a low-pressure wave at the exhaust valve when it opens depends on the length of parallel pipes of the exhaust manifold. That's why basically instead of cast iron (stock market) exhaust manifold, headers( aftermarket exhaust manifold) are used mostly in order to get better performance.

       
      •  In case of single cylinder engine :
     

IN THE ABOVE IMAGE, CLEARLY, WE SEE THAT LOW PRESSURE REFLECTED BACK WAVE OPPOSES THE INTAKE CHARGE TO FLOW ALONG WITH THE EXHAUST GASES SO THAT THERE IS NO MIXING OF INTAKE CHARGE AND COMBUSTED GASES. SO, HIGH DEGREE OF EXHAUST SCAVENGING TAKES PLACE

3.Anti - Reversion :
      Due to more back pressure, the reversion of exhaust gases into intake manifold takes place.Due to which volumetric efficiency decreases thereby decrease in HorsePower.By following anti-reversion methods we can increase volumetric efficiency.
Methods :
• by using turbochargers ( creates positive pressure )
• by making changes in intake and exhaust manifold design.

     In the above image, there is a tapered geometry included in the design of exhaust manifold as well as the intake manifold. Due to increase in area, the intake charge in the intake manifold and exhaust gases in the exhaust manifold will expand suddenly causes low-pressure waves which act at the respective valves when they open (as mentioned in exhaust Scavenging above).So these low-pressure waves will help to suck both intake charge into the cylinder and exhaust gases out from the cylinder due to the pressure difference.

4. Reverse Restriction :
        Due to the design, as shown in the below image, the back pressure waves won't restrict the flow of exhaust gases. They will cancel out each other at the area as shown in the figure. So there is no effect of back pressure that results in more HorsePower and increase in engine efficiency.

     

 # These are the methods to make changes in the exhaust system in order to increase performance. Apart from this, going for individual replacement of performance exhaust system parts like aftermarket headers, catalytic converters, mid pipes, resonators, mufflers etc may also increase Horse Power depends on the type of engine you are using.Generally, automobile companies follow the principle behind the above four processes and based on that they will design the exhaust system.To my knowledge, the best exhaust system present till today is header back exhaust. But you have to think about that whether it fits your vehicle or not #