Folks I will post a real world comparison next week. I have a set of untouched factory 71 A-body 340 manifolds as well as an identical set that have been Extrude Honed, both will be tested on the same engine with no changes and the same pair of exhaust pipe extensions. Keep in mind that any gains (or lack of) may vary with ANY engine combo, it's all about where the engines "bottlenecks" are, if it's the exhaust manifolds (which is what I expect mine will be) you might see a bigger gain with EH manifolds, in my case will will soon see.