Malossi Velocity Stack 05 0232 for Dellorto PHF and PHBE carburettors with a 48mm intake thread. 

Also known as Ram Tube, Bellmouth, Air Horn or Velocity Stack. This 61mm long Alloy Trumpet suits all Dellorto PHF carburettors.  The 48mm offset threaded part allows the flow of air to integrate seamlessly into the carburettor without the step that occurs with no offset. An Alloy Riser is available to raise the rear of the tank and a Rubber Cover to prevent ingress of dirt/dust when the engine is not running. It is advisable to use an Additional Foam Type Filter to protect your engine. This velocity stack and filter combination is fitted to DAM Classic Racing 1000cc and 1200cc race bikes.

HOW IT WORKS:

It is commonly mistaken that "stand off" (air–fuel mixture that gets pushed back out of the port, usually when using full throttle at low rpm) is somehow captured by installing a longer intake pipe, but it is actually that the intake valve is closing too late and the combustion chamber is simply overfilling and blowing back out the intake port before the intake valve closes. Installing Velocity Stacks creates a later intake pressure wave that helps keep the air in the chamber until the intake valve closes by functioning as a resonating pipe which adjusts the frequency of pressure pulses based on its length within the tract.

Power gains in the order of 2% to 4% can be obtained when inlet radii and stack lengths are optimized for the  engine.