Whats Scavenging Effect, anyway?
The ultimate performance gains are to be found when an exhaust system, including the mufflers, creates a scavenging effect. This can increase horsepower, torque and fuel economy, all at the same time. Scavenging is when a [reflective] low-pressure wave comes back up the header pipe, says Muffler Guru. You want it to get back to the exhaust valve when the engine is in overlap. It creates a low-pressure area at the exhaust valve and aids in the induction charge, … getting your intake flow started into the cylinder. The diameter and length of your exhaust pipes, your muffler design and your cam timing are all factors that affect scavenging. When you get this optimized, says Guru, you can get a boost in torque. Between that tuning and the intake manifold tuning, thats how you can achieve over 100 perfect volumetric efficiency on a naturally aspirated engine. A variety of high-performance mufflers are designed to enhance this scavenging effect.
