What is Back pressure in exhaust ?

Logically I find it is not good. (resistance to flow )


What pipings are used for bike exhaust.

How is length and resonator decided?

The term back pressure is totally wrongly interpreted and therefore badly misused.

The confusion might come from the fact that when increasing the bore size the low end torque gets less the more the size is increased.

Primaries, secondaries and collector pipes are in a mathematical relation. Changing any of them randomly does throw the balance of the system. This goes for lengths and diameters.

The basics of the design depends on the engine configuration, which is the number of cylinders, configuration (V, angle of V, W, VR or straight), individual cylinder volume, cam characteristics and intake as well as desired peak power point.

With uneven length primaries and/or stepping them the torque band can be widened. If an even narrower torque band is required then secondaries are being left out, which is not possible with all configurations.

This is only the beginning of the problems. Much more detailed work is needed to get the desired effect, which people would like to refer as the correct 'back pressure'.

Back pressure means not to produce pressure inside the pipe but to increase velocity of exhaust if I may put it like this ?

multijet wrote:

Back pressure means not to produce pressure inside the pipe but to increase velocity of exhaust if I may put it like this ?

Actually, it is ayes and a no at the same time. The velocity changes all the time because of the pulsing. And the pulsing is what makes the exhaust system design rather complex. Once you have more than one cylinder the pulses can help the exhaust gas evasion if timed correctly. This is by dragging and pushing each other out of the system. Additionally, it can help the scavenging.