How Do You Determine Exhaust Header Size

First, divide the engine’s total displacement by the number of cylinders to get the cylinder displacement. Then, multiply that by 0.80 for a typical street engine or 0.90 for a tuned race engine. For boost pressures under 14 psi, calculate using the exact displacement.

How do I know what size headers I need?

Horsepower OutputPrimary Diameter200-325 hp.1 1/2 in.275-425 hp.1 5/8 in.400-500 hp.1 3/4 in. or 1 7/8 in.500 hp. or more2 in. or larger

What are tuned length headers?

A tuned exhaust header’s primary-tube length has a direct influence on engine performance. It controls where in the engine’s speed range the header will add performance. Longer tube lengths pull the torque down to a lower speed. Shorter lengths move the powerband up into a higher speed range.