Header Sizing Calculator

Notes: I encourage you to read the header design article.

The calculated primary diameter is INSIDE diameter, you will need to add wall thickness to get your desired OD. For example, if you are using 16 gauge tubing it has a 0.060" wall thickness, so you will need to add 0.120" to the result.

Peak horsepower RPM is used to size the primary diameter, tuned length RPM is used to calculate where you want the primary length to have the largest effect. The header primary length is calculated from the backside of the exhaust valve. If your exhaust port is 2" and calculator result is 36", you will need 34" long primary tubes.

A good starting point for exhaust gas temperature is 1200 F for a midrange NA performance build. A good starting point for desired exhaust gas velocity is 300 ft/s to get a useful scavenging effect.