Lukey are now making a bi-modal muffler that works in a similar way to all the new exotics and high end muscle cars.

They have a spring loaded flap so under idle and light accell the flap is closed forcing the gas to go thru all the baffling but at high revs the pressure opens the flap and it turns into a straight thru type muffler.

Sent from my custard cannon like Peter North.