Join Date: Aug 2009
Location: Washington, the state
Very interesting technology. Here's more explanation of what's happening in general in an exhaust system, an one can visualize how this exhaust tuning valve can change the characteristics of the exhaust system for optimizing the scavenging at different rpms, and it is not about back pressure per se
"...there are two main phenomenon occurring in the exhaust, gas particle flow and pressure wave propagation. The objective of the exhaust is to remove as many gas particles as possible during the exhaust stroke. The proper handling of the pressure waves in the exhaust can help us to this end, and even help us “supercharge” the engine.
"As the exhaust pressure wave arrives at the end of the exhaust pipe, part of the wave is reflected back towards the cylinder as a negative pressure (or vacuum) wave. This negative wave, if timed properly to arrive at the cylinder during the overlap period can help scavenge the residual exhaust gases in the cylinder and also can initiate the flow of intake charge into the cylinder. Since the pressure waves travel at near the speed of sound, the timing of the negative wave can be controlled by the primary pipe length for a particular rpm.
"The strength of the wave reflection is based on the area change compared to the area of the originating pipe. A large area change such as the end of a pipe will produce a strong reflection, whereas a smaller area change, as occurs in a collector, will produce a less-strong wave. A 2-1 collector will have a smaller area change than a 4-1 collector producing a weaker pressure wave. Also, a merge collector will have a smaller area change than a standard formed collector producing a weaker wave.
"So, the trick to proper exhaust tuning is to tune an exhaust system is produce a negative wave of the proper strength timed to occur at cylinder overlap."
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