I posted dyno results from my header install some time ago. One of the older threads about it is here:

https://mustangforums.com/m_1737964/tm.htm

In a nutshell, I got somewhere between 15-20 HP AT THE WHEELS with the Dynatech longtube setup. That is WITH CATS and running a tune from Brenspeed (not a custom dyno tune). Read the thread for a discussion on my exact results.


Here is a past thread about LT and smog legality...worth a read:

https://mustangforums.com/m_1814805/tm.htm



Regarding the Kenne Bell notes: While I do trust Kenne Bell as a good company, we don't know under what context these notes were written as they provide little background information. For example, it says they tested "headers" and found no gains. But what headers did they test? They don't say. It could be they tested only shorties, which are known to have minimal HP gains. Modular Mustangs & Fast Fords tested shorties and got between 3 and 5 HP from them. It also could be the results of tests on an already supercharged car. With forced induction scavenging becomes much less of a factor than it does on an NA car....