He only picked up 6 RWHP/RWTQ from that swap. Yes there are nice gains over the curve, but that's not enough to pick up as much as he did IMO. Something else had to have assisted that better time other than the header swap. You know as well as I do that 6 RWHP isn't going to shave 2 tenths on these cars

 

Peak rwhp means nothing, that's why everyone talks about the horsepower integral, and not peak numbers. One would expect to gain little peak power based on header theory, but gain more torque with a longer tube as they are more efficient at lower engine speeds- i.e. better low rpm scavenging = better low rpm torque..

This doesn't disprove his results at all- just shows your level of header theory understanding.

Studytime

 

You can get dyno gains like this from an LS6 intake over an LS1 intake also but you won't see .2 sec gains from the swap.

You also need to look at the Y. The Mac is a 2.5" Y the Grott is a 3".
Again, there is more to this than just header length, and 1 person getting decent gains does not mean anyone else or a majority of people will get the same results. You need to look at the average gain on several cars.

If you have any science background you'll know as well as I do that 1 experiment is not enough to be conclusive.