I'm having a custom one made for my astra turbo. It will be 2 1/4 inch in diameter free flowing with twin 3 1/2 inch diameter tail pipes. What I would like to know is why would it be quieter than my existing exhaust on idle? Well that is what the chappie informed me, but he didn't say how loud it would be travelling down the road. I thought that the less back pressure and crap in the rear box would make it louder. Btw, only costing me approx £250.