One thing is clear, some have had good results while others have not. Knowing how to use what you have (not limited to the heads here today) and how stuff works is half the battle.
The flow curve of the head is the first hurdle and how much port you have (CSA) is another aspect people look past. Smaller item like port shape itself is yet another issue.
Is it a low laying port (AKA stock heads) or a raised port? (AKA W5/W9's etc...)
Bottom line, it's the whole package!Oh I agree Rumble but I paid a LOT of money for these knowing they would never flow the claimed 319 cfm or whatever but I fully expected a solid 300 cfm and good mid range flow. Guess what?! I don't even want to talk about mid lift flow and 284cfm with a TON of help?! Burn victim over here throw some water on me! J.Rob