Megan Header Dyno Results

[Doc Zaius]

Alright... I started doing a bit of poking around and reading online as to the relationship between "backpressure" and torque, and why free-flowing headers and exhaust systems can decrease the amount of low/mid torque. People assume that since a more restrictive muffler/header/whatever has higher low-end torque, then it must be because of increased backpressure. Right? Wrong! Its b/c with a smaller diameter exhaust system, the exhaust gasses move faster. These faster moving gasses produce a slight vacuum behind them, which actually helps to pull the remaining exhaust out of the cylinder. This process is known as "scavenging". Otherwise, these gasses would be left in the cylinder, displacing new, fresh air/fuel, and thereby producing less power. As the engine speeds up (higher RPM), the scavenging effect is less pronounced, and the exhaust system's ability to flow gasses makes more of a difference, which is why the megan header works very well at very high rpm.

For some better information on this, please check out the following two very good quick-reads: Exhaust: The straight scoop on backpressure and Exhaust system backpressure.

Any thoughts/comments?