Join Date: Jun 2007
Location: Alexandria, VA
Vehicle: '07 SLK55 030
Mentioned: 2 Post(s)
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Thanked 132 Times in 71 Posts
If he's looking to replace headers, a secondary cat delete wont be too much, though it definitely is noticably louder. I also did xpipe first only, but went back for secondary cat delete a month after. That being said, my girlfriend to this day has no idea I changed anything. It's still relatively quiet when driving around normally.
You are correct that you will need an ECU tune. There are companies who can do it wirelessly over the Internet. Even on a dyno if you want so they can tune to your car specifically.
Sold: '07 SLK280 | 18" TSW Bremmas | Toyo T1-R 225F/245R | SmartTop V.3 | Green Filters
Sold: '07 SLK55 AMG | 030 Package | Custom X-Pipe | Secondary Cat Delete | SmartTop V3.33 | Mod R170 Antenna | BC Racing Coilovers | Racingbrake Two-Piece Rotors | Enkei Pf-01, Michelin Super Sport 245F/275R
Current: '15 Alfa Romeo 4C | Black on Red | Track Package