Ever thought of one of these? :)
http://www.sub5zero.com/auto-news/remot ... z-roadster
(a manual version)

Those are servo controlled by the ecu, and the backpressure tuned to the fuelling & exhaust to produce more low end torque which a large pipe kills..

Manually controlled? You mean like a direct cable couple to the throttle? Jesus that'd be horrible...

The link he posted is nothing to do with low end grunt etc, its purely to cap the noise level in neighbourhoods etc.
Not worth a wank!