exhaust pipe diameter for a mildly modified 340

ir3333 said

i think this thread is finally dead so i'll just throw this out there. The last info i read (that was way over my head) said at lo rpm 1lb. back pressure kept the cylinder filling, overlap and scavenging events uniform.
I can hear those murmurs!

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Makes no sense. At least no sense without context. What's the pressure in the intake? Where was the pressure in the exhaust measured? Are they measured on the same scale? Modern cars use absolute pressure. Atmosmopheric pressure is 14.7 psia. 1 psia is very low pressure.
This is why I recommend Calvin's way of looking at exhaust flow. Its focused on the most important job of the exhaust system, not on a limited rpm range.