This is how it goes.

Every car is different.

Headers work.

Headers don't work.

Like already stated, every car is different.

I couldn't run knock free without them.

My buddy ran a 3.4" knock free with a u-bend deleted and the cat hollowed out. Stock PCM...stock everything.

So get a way to scan it...whatever keeps you mostly knock free, will work. 2-3* isn't the end of the world, especially on larger pullies.