Your talking about the exhaust deflector right. Like the green thing on pic below. It does something to your low/high end? the longer ur stinger is or something like that, but nothing too major. Ive used mine for a while now, lately i dont use it because it makes the exhaust noises sound funny. Aslong as the diameter is the same as the pipe, the flow shouldnt be restrictive

If your into drifting maybe you should get a stage-d kit, i know its expensive but it does make a difference. You can make stage-d kits with full rear exhaust (very bottom pic)