Thanks Umang.

**Calculating Primary Pipe Length And Diameter.** **Exhaust pipe length and size. why we need this?**.

As the exhaust valve opens, a positive or pressure wave front is created which travels down the exhaust pipe at the speed of sound. As this pressure wave reaches the end of the pipe, it expands and a negative or suction pulse travels back up the pipe towards the engine.

As the negative wave front in turn reaches the cylinder, it reverses again and moves back towards the end of the pipe. This fluctuating pressure pulse effect can be used to great advantage in tuning the engine.

If the system is designed in such a way that the negative or suction pulses return to the cylinder at overlap T.D.C., then they will assist in clearing the combustion chamber of exhaust gases.In turn, this will cause a depression at the inlet valve, which will help draw in the inlet charge.

The following formula can be used to calculate the ideal length for Primary Pipe Length:

**LengthOfPipe = (129540 x E.T) / (R.P.M. x 6)**
Where:

L = Primary pipe length in mms measured from the exhaust valve head.

E.T. = Exhaust valve duration in degrees from point of valve opening before B.D.C plus the full 180 degree stroke up to T.D.C.

**(Assumption*)**
(Reverse calculation for the stock exhaust to get this value)

R.P.M. = The estimated revs, at which max. power will be achieved minus five hundred.

**Example:**
Estimated maximum power R.P.M. = 7500

E.T. = 15 + 180 = 195 ~ 210

R.P.M. will be 7500 - 500 = 7000 (Max Power @7500 and FZ16 Redlines at 9000rpm)

Result Primary Pipe Length: L = 600mm ~ 650mm (based on the ET Values 195, 210 Respectively)

**Having calculated the primary pipe length, we must now calculate the diameter as follows :**
Divide "L" by 10 to bring it to cms. Call this "L2". (60)

Take the cylinder capacity in ccs and double it. (Say 153 x 2 = 306)

Divide by "L2" as previously calculated. (306 / 60 = 5.1)

Divide by 3.4 (5.1 / 3.4 = 1.5)

Find the square root (√1.5 = 1.225)

Multiply by two and add 0.3 ((1.225 x 2) + 0.3 = 2.75)

Multiply by 10 to bring it back to mms. (10 x 2.75 = 28) = 26~28mms. (Diameter based on ET Values) - I have taken this as 35mm as, we don't have negative pressure from other cylinders as this is a Single Cylinder Engine.

**NOTE : **
The Above Calculation is for Multiple Cylinder - for 4-2-1 or 4-1 Pipe configuration.

Above length is the Primary Pipe Only

Tuning

**Assumption is the Mother of all f^%$-ups. *