Exhaust in 4 stroke 1 cylinder

[aryo]

want to ask some question about exhaust system :

1. how to determine the diameter and length of header pipe,determine the size of muffler, determine the baffle (basic calculation) in 4 stroke 1 cylinder engine ( generally in motorcycle )?

2. what is back pressure? whatz the effect on performance? how to avoid back pressure?

3. i want to give valve on my motorcycle exhaust pipe (4 stroke 1 cylinder, 107 cc)like EXUP system in yamaha and Suzuki Exhaust Tuning (SET). is it good? how to determine the valve position and the mechanism of the valve, so it can open and close depend on engine rpm?

thank u for the attention

 

[Rob45]

The answers to your questions could fill a book; some fairly pricey software from Ricardo, for example, will evaluate exhaust system designs, can give pipe length and diameter recommendations.
What you'd need to do is size the pipe for the flow rate, determine the pipe lengths based on valve timing, intended operating RPM or RPM ranges, and gas temperatures.
(Gas temperature gives the speed of sound in the exhaust stream for use in calculating pipe tuning)

Exhaust backpressure is the pressure in the exhaust system, usually greater than atmospheric pressure, which tends to resist the flow of gases out of the cylinder during the exhaust stroke. Backpressure reduces engine performance if there is sufficient valve overlap such that the backpressure prevents complete scavenging of the exhaust gases and complete filling of the cylinder.
Therefore, the effect of backpressure on performance is greater with larger degrees of valve overlap and higher valve lift, as in high-performance two-valve engines, and the effect is much less in 4-valve engines, or low-performance 2-valve designs (e.g., tractor engines, etc.).