Velocity Stacks — For Looks, For Power, or Both?

By John Wilhoit

We tested 6" vs. 2.25" velocity stacks mounted to Weber 44IDF carbs on one of our 1925cc single plug engines. There was a change in the torque curve and (interestingly) no significant change in the fuel curve. There was an improvement of about 3 ftlbs in peak torque but a loss in the upper range. I determined the improvement to be insignificant when considering the weird look of such a tall air cleaner. Incidently, we've tested with and without air cleaners and have consistently seen no improvement by eliminating the K&N air cleaners; on the other hand, the Porsche factory mesh cleaners do have more restriction compared to the K&N, so eliminating them or switching to K&Ns will bring an improvement in horsepower. Using a filtering screen over the top of velocity stacks instead of an air cleaner will seriously affect the flow and should be avoided. (Click here to view a larger image of the curves shown below)

Reprinted by permission of Wilhoit Auto Restoration

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