Aftermarket Exhaust Parts - Common Aftermarket Exhaust Parts - Headers

Headers

Switching from an exhaust manifold to exhaust headers (also known as extractors in Australia) will optimize the exhaust gas flow speed and in turn increase the high-end power of the engine. This is done by using an individual pipe for each exhaust port that has smoother bends with a larger turn radius, decreasing airflow resistance, as well as a calculated pipe diameter to obtain a good scavenging effect for the specific engine capacity. The pipes then merge into a collector and then flow into a larger pipe (down pipe), just before the catalytic converter. With equal length headers, as each exhaust valve in the head of the engine is opened and exhaust gas is forced out, it passes down one of the header pipes and through to the down pipe, where the exhaust gas velocity causes a slight vacuum in another header pipe. This has an effect of scavenging exhaust gas from the cylinder, which is beneficial for performance. In performance engines, which have cam overlap, the scavenging effect will pull air through from the intake manifold as well, further increasing performance. The length of exhaust headers can be tuned to perform best at specific RPM ranges. Stock exhaust manifolds are usually made of cast iron and can be restrictive. Headers may or may not increase the dB level of the exhaust, depending on the original exhaust manifold it replaces and the engine. However, the pipes do "ring" with the exhaust pulses and increase underhood noise. Headers can be ceramic coated to reduce the heat radiated in the engine compartment, and to increase the temperature of the pipes which increases the velocity of the exhaust gases.

Terminology:

• 4-2-1 Headers where 4 pipes merge into 2 which merge into 1 (tri y's). There are different opinions as to which cylinders in the firing order should be paired for best effect. In a V8 the pairing tends to join cylinders with similar firing intervals, and this will differ between left and right cylinder banks.

• 4-1 Headers where 4 pipes merge directly into 1

• Shorty Headers where the total length of the header is shorter, with the collector closer to the engine

• Equal Length Headers where each exhaust pipe is the same length from the exhaust port to the collector cup