We began seriously working on the development of Velo Stak early in 2015. The first versions featured spiral grooves in the bell mouth and the intent was to spin the air entering the carburetor. By doing this, we theorized that a larger volume of air could be forced into the carbs, thereby increasing power. Well, tests on a flow bench actually showed that the grooves did not increase air flow over a velocity stack with a smooth surface. While both the smooth and grooved surfaces flowed air very well, there was no real advantage to using the more complex surface treatment.
The first prototypes were short and one piece. There were a few design issues with this stack. First, the length was not really beneficial for racing as longer stacks are desired for that application. Also, we were concerned that there was no consideration at all for debris (small stones, tire marbles, etc.) entering the carbs while racing. The solution– at least part– was to redesign the stack to be made in two pieces with allowance made for an aluminum debris screen fitted between the two parts. This helped but we still had to deal with the length issue. As we had intended to make Velo Staks usable on street as well as race cars, we considered making two or three versions of different lengths but this proved to be an awkward fix. In a moment of clarity and brilliance, Bob realized that if we were to make the stacks in two parts with the mount and tube as one piece and the bell mouth as the other, then the tube could be made long with the option of cutting it shorter, if desired.
Initially, the bell mouth was fastened to the tube by means of a zip tie but this was eventually replaced by an arrangement whereby a small machine screw and nut would be used to clamp cast-on lugs on the bell mouth casting. We discovered that both of these fastening treatments had their design limitations. It was difficult to get the zip tied version fastened tightly enough to the tube to make it secure and if over tightened even a bit too much, the cast-on lugs would sometimes distort. In time, the current design was tested and accepted as the best solution to the assembly issues. The bell mouth is now cast with the tube attached and the tube is firmly held in place in the carb mount with a few drops of cyanoacrylate adhesive. Simple and very effective.
The most significant and visually enhancing development came with the replacement of the spiral grooves with dimples (see The Advantage of Velo Stak in the Technical section for a detailed explanation of why dimples work). A few other refinements like moving the debris screen much farther into the tube (as not to disrupt air flow in the bell mouth) and the development of a reverberation calming “ratchet” into the base of the stack (again, please refer to Reverberation in the Technical section). We have been working on Velo Stak design for almost three years and during this time, we’ve learned a lot about what a great velocity stack should be and what it should do. We are never willing to accept ‘good enough’ and are constantly striving to improve the product. We believe that Velo Stak is the most technically advanced velocity stack available today with design features and practical attributes not available from any other manufacturer.