Adding a Velocity Stack


I thought I'd give this a shot. I would like to put a velocity stack on a Mikuni HSR45 carb. It will be inside a K&N round tapered air filter, the end of which is flat. How much space should there be between the mouth of the stack and the inside of the end of the filter in order for it to function properly? The stack is not so much for tract length tuning as it is for straightening the airflow and reducing turbulence at the entrance to the venturi. 

Thank you,
Lee Halverson



Unless this is an ultra high rpm engine (10,000 rpm), the stack and filter will not make for much difference. The airflow is not “super sonic” like some people think. The carb will pull in what it wants. Try it without the filter, get a baseline performance, and then add the filter. If performance goes down, add length and volume until there is no difference. It will take you long. 




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