Hello, the length of pipes and diameter is determined by where you want the power band.. What I mean by this is what rpm range do you want to be your max VE?
here you go.. this might get you going in the right direction..
To calculate exhaust header size and length for optimal scavenging, use formula \(L = \frac{850 \times (360 - \text{EVO})}{\text{RPM}} - 3\) for length (inches) and determine primary diameter based on engine cylinder displacement and target RPM, usually targeting high-velocity flow. Key metrics include the exhaust valve opening (EVO) timing and peak torque RPM. [1, 2, 3]
Exhaust Header Formulas
Primary Pipe Length (HPL):
\(L=\frac{850\times (360-\text{EVO})}{\text{RPM}}-3\)
EVO: Exhaust Valve Opening angle before bottom dead center (BBDC).
RPM: Desired peak torque RPM.
Alternative: \(\frac{850 \times \text{Exhaust Duration}}{2 \times \text{RPM}} - 3\).
Primary Pipe Diameter (HPD):
First calculate desired Primary Pipe Area (PPA) (sq. inches) = \(\frac{\text{Cylinder\ Volume\ (cc)}\times \text{Gas\ Velocity\ (ft/s)}}{3370\times \text{RPM}}\).
Then use: \(D = \sqrt{\frac{4 \times \text{Area}}{\pi}}\).
