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

September 26, 2010 | Troubleshooting & Repair

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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