Had my headers on for about 3 months...
Power definitely can feel it and hear the engine now.
All threw redline it pulls hard.

And I have my setup only with k&n high flow with stock 3.0i back of the headers.

I am waiting to Shark it.
But how it is now it already increased the red line just with header install.
Before engine felt stressed if going around 4500 to 5k rpm.
Now I can recline and engine really puts the power down.

Strange thing for me is I'm getting precat o2 cel.
Bank 2 sensor 1 and I'm running the 02 90° spacers

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2001 e53 5mt
Stainless steel headers
UUC short shifter
Lowered on bc racing coilovers