Akrapovic Evolution Line Cat Back (Titanium) W/ Titanium Tips - BMW / E9X / 335iS BME90 91 335 The next stage in revolutionizing the performance of the 335i, beyond the Slip On option, is the Evolution exhaust systems. These systems, which are made entirely of stainless steel or titanium, can save 12 kg or even a full 21 kg of weight, depending on the material. That we made no compromises can be seen in additional power and torque, but its not all about providing more peak power. There are also noticeable refinements to the