Rode an 18 test FXBB (stage1, tuner) with the SE extreme Air filter double radius and they killed the bottom end , got going from around 3500 though,I have the same bike(Stage1,tuner) with the Se extreme air filter and V@H 3.5 Slash cuts,it has more grunt than the bike with the double radius from idle to around 4K , I thought they were too loud so I put those DK torque inserts in and it toned it down a little and FELT like it picked up some low end torque. They are much lighter than the stock HD mufflers too.