aFe 21-23 Subaru Crosstrek Silver Bullet Throttle Body Spacer KitaFe 21 23 Subaru Crosstrek Silver Bullet Throttle Body Spacer Kit The Serrated Helix combination design creates intake turbulence in the combustion chamber. This turbulence breaks up the fuel which creates a more complete combustion cycle increasing horsepower, torque and improving throttle response. The Serrated Helix combination design also reduces intake whistle that occurs with Helix only designs. All Silver Bullet Throttle Body Spacers are