These velocity stacks are machined from 6061 billet stock on modern CNC equipment.  They are a direct replacement for the small plastic stacks found inside of your airbox.  These velocity stacks only require a very small modification of the airbox to fit.  (the hose support needs trimmed)  The use of a "Flow-Commander" or re-jetting of the carbs may be necessary to take full advantage of the design.

NOTE: This item is back in stock. (sorry for the delay)