I've had my Kleemann headers for 1 year now and i'm more then happy with them
Better sound, my car gained aprox 20-30 WHP combined with the special ECU tune.
It made 420 HP and 600 NM with headers+downpipes,exhaust and special ECU tune. If i would have added cams to that it would have landed on aprox 430-440 HP with a new ECU tune.
But i stopped there and bolted on a Kleemann supercharger instead that just have been installed

So my 420 HP 600 NM turned into 538,7 HP a few days ago in Kleemanns dyno at only 0,4 bar boost.
Ask me if i'm happy
// Magnus