304 Stainless Steel
Civic EG EK EJ B16
4-1 headers are designed so that all 4 exhaust pipes merge into one. In most dyno tests this produces the most top end power since it usually offers the best flow characteristics for the engine at high engine speeds. 4-1 headers usually move the power band up which makes the bottom of the RPM band feel a bit weak and the "seat of the pants" feel might not be as strong as a 4-2-1 header. However dyno tests have show that at low RPM there is very little difference in power. The 4-1 headers usually have less back-pressure than the 4-2-1 header and customers have stated their cars seem louder at high RPM with the 4-1 headers.