[Joe-Touring]

Originally Posted by JUDGE3

to explain where i'm at: posted my cam because several had stated my cam is a problem with the rare round port exhaust manifolds. specifically the 110 lobe separation. wanting to learn why?

The big reason why equal length headers are the hot ticket is due to exhaust scavenging.


A good set of headers that have a well designed collector(v important) will flow more CFM than the diameter of the tubing would suggest. This is because of the scavenging effect. When an exhaust valve opens and the gases move thru the primary tube and past the collector, the other 3 tubes will then be affected by the low pressure zone following the high pressure pulse. This helps draw out the exhaust gases from the next cylinder. I think this is a simplistic explanation, there’s other factors, resonance/heat etc.

Lobe separation comes into play because it’s directly related to overlap(intake/exhaust valves open at the same time). While both intake/exhaust valves are open, the scavenging effect moves into the intake, drawing more fresh air and fuel into the cylinder.

From what I understand, ram air manifolds like 112-114 degrees LSA.

Quad in post 6 linked a good reference:

Originally Posted by Quad

SD performance have a good tech article on this topic. RARE OS manifolds can make almost as much power as headers. OR a lot less. Link below explains.

https://www.sdperformance.com/moreTech.php?newsID=39