I've been informed that the following rule from the ACU handbook will strictly be enforced at this years Manx GP


"Exhaust Pipes
1. The end of the exhaust pipe or pipes must not project beyond any part of the vehicle or its bodywork. Exhaust gases must not be discharged so as to raise dust or foul the tyres or brakes, or inconvenience a following rider. The end of the exhaust pipe for a minimum distance of 30mm must be horizontal and parallel (within a + or -10 degree tolerance) to the fore and aft centre line of the machine. It must not extend beyond a line drawn at a vertical tangent to the rear edge of the motorcycle rear tyre."

And I'd guess that it applies equally to the TT