Downpipes and physics

[Dead Eye]

The term back-pressure is somewhat mis-understood I believe. The idea is that you don't want negative pressure such that gas flows IN to the exhaust ports. As the gases are released in high pressure pulses, you need to have a suitable system to prevent the negative pressure behind the high pressure pulse from becoming an issue - at least this is how I understand it and I could be wrong, but it makes sense in my head.

This explains Motads research into their "Serpent" pipes - they described a negative pressure effect on the inner curve of the first bend caused by the gases being squashed against the outer edge as their direction (vector) changes - by squashing the pipe at this area, it prevents the negative pressure area from developing in the first place as the gas fully expands in to the narrower pipe section... and I should probably stop rambling...

Back to the oval topic, would this shape (and others) not create varying pressure values when measured at different points on the cross-section of the pipe?