As most folks here know, its all about the combination. A long time ago when the firing order swaps were new I saw Dick Maskin asked about it. This was close to the time when he built Pro Stock engines. He said when they originally went to it they did not see any power increase. However since they thought it made sense they stuck with it. He said later after they had continued to develop their Pro Stock program they found that if they went back to the stock firing order they lost horsepower. He could not explain it so I certainly won't try.