403 Forbidden. It OK, really. The part about exhaust valve timing is enough for me.
OTOH, the phrase 'coanda nozzle' is magical. I've been looking through Google images. I found a post by basjoos on some gas saver forum in 2006 that pointed to a .pdf titled
SAE TECHNICAL PAPER SERIES***2001-01-2072
Advanced Aerodynamic Devices to Improve the Performance, Economics, Handling and Safety of Heavy Vehicles
which is awesome. Dynamic aero control with valved exit slots. Instead of a boat-tail, you can push the rear of the vehicle around with pumped air, and get drag reduction or air braking.
And this patent drawing suggests the exhaust tip might be better serrated than bellmouthed:
