Exhaust flow talk

[Ivan141]

@ Banpei, you're not entirely correct. NA tuning involves cams with long opening times and thus bigger valve overlap. Just read in the link you posted... a little quote:

Quote:At high rotational speeds, consistent flow through the intake and exhaust ports is maintained by allowing the intake and exhaust valves to be open simultaneously at top dead center (known as valve overlap). The momentum of the exhausting gas maintains the outward flow and creates a suction effect on the cylinder known as scavenging, helping to draw the intake charge into the cylinder

The theory is much the same as 2-stroke technology, just less critical.
Think about it...what would be the use of tuned 4-1 or 4-2-1 headers if the pulses didnt aid in scavenging as it is called a few posts back.
A turbo engine on the other hand benefits from having very little overlap.