On a standard engine, burnt exhaust gases are dumped from the combustion chambers (cylinders) into a single piped manifold, which is attached to the exhaust pipe.
This dumping causes turbulence in the manifold since there is not enough space for all the exhaust gases. A higher level of engine back pressure is created, wasting some engine power forcing the exhaust gases through the exhaust system. This increased back pressure reduces the inflow of fresh air and fuel, resulting in fuel combustion efficiency being reduced, causing the engine to run hotter and wear faster.
Extractors provide more pipe volume for high efficiency exhausting and thereby allow a better mix of fuel and air intake.
