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Originally Posted by taxonomy  This is where we part company. If you are interested take a look at the link I posted above or at SSearchVT's post earlier in this thread.
Most of the efficiency gains are pulse timing and scavenging from what I have read. Lyle Cummings is another pretty good technical writer about this stuff. Heir to the Cummings engine fortune.
Anyhow, if you look around and dig into the SAE kind of stuff I think you'll see it's pulse timing. This is my understanding of it anyhow. |
Pulse timing and scavenging are only two of many variables that affect the efficiency or performance (they're not necessarily related) of engines.
Pulse timing is a result of gas flow and engine harmonics (combustion occuring at a certain rate, and being pushed through a pipe). But the geometry, material, surface condition, and temperature of the pipe all play a role.
All of the variables need to be considered - starting from the air before it passes through the filter, and the fuel in the tank - and ending with the exhaust gases as they exit the tailpipe - for a true statement to be made about performance or efficiency. You will also get different results if the engine is on a dyno or in an actual vehicle (ram air affect, and the pressure area around the tailpipe).