Stealth baffle
 

Obviously I'm not trying to encourage illegal behaviour, and this probably won't fool an MOT test but might pass more a more visual roadside test?

Not going into details, as that might be seen as encouragement, purely intellectual curiousity you understand. Think "hacksaw".

http://www.mattandem.plus.com/images/baffle.gif

And yep, some baffles will be straight through rather than expansion chamber, the idea's the same. And yep, little Matty's art work has really come on leaps and bounds this last school term :)