Just wanted to let you guys know that RPI is coming out with a new system for the 135i! RPI always dyno test their products and will NEVER release a product that does not make substantial gains. According to Eloy@RPi, he's going to make this system a true dual with quad tips. He'll also provide your with templates to cut your bumper to fit the quads. For those worried about cutting their bumper, the stock replacement piece is $50 from the dealer. This exhaust will have a lifetime guarantee and performance guarantee. I will have some pictures of the prototype and dyno up soon! To get an idea of how it sounds, here's a similar exhaust on a 535i.