PSI Genesis "Big-Air" Carb - First Look

PSI specializes in the design, testing, and manufacturing of innovative high-performance products for the snowmobile, motorcross, ATV, and Harley-Davidson V-Twin marketplace. PSI began in a three-car Wisconsin garage in 1983, building 2-stroke exhausts systems for the MX and snowmobile industries. By '85, PSI moved into a 30,000 square-foot building with a SuperFlow dyno and grew to over 40 employees. In the '90s, PSI became involved in Personal Watercraft racing and was picked by Seadoo to campaign one of its national race teams. During that time, PSI also developed Genesis snowmobile engines that produced 200-300 horsepower reliably and could be trail ridden or raced. Today, PSI snowmobile engines produce between 350-500 horsepower.

About eight years ago, PSI received two patents for unique carb designs for its snowmobile engines and received "best engineering" awards for them. As it turned out, some of PSI's snowmobile customers, who also ride Harleys, recommended that PSI adapt its unique carb technology to the V-Twin engine. Over the past two years, PSI developed its idea of the perfect fuel mixer for the V-Twin industry: the Genesis "Big-Air" carb.

Design objectives for the Genesis Big-Air carb included high airflow, excellent fuel vaporization and throttle response, the ability to throttle smoothly without an accelerator pump, simple tuning with easy external adjustments, and the ability to meet 2010 emissions standards. Of course, the new carb required rockin' good looks and had to be American-made out of the highest quality components. Straight out of the box, PSI's Patented Genesis Big-Air carb screams, "I am different." And different it is. According to Bruce Kahlhamer, President of PSI, the Genesis Big-Air carb satisfies a wide range of engine displacements because of its unique design.

The 48mm PSI carb is machined from high-quality billet aluminum and has a variable venturi controlled by a hard-anodized flat throttle slide supported by eight roller bearings (four per side) for smooth operation. The benefit of a variable-venturi versus a fixed-venturi is that because the size of the venturi varies based on throttle position, air moves through the carb faster at part throttle for improved fuel atomization and throttle response at low-rpm operation. However, that said, the flat slide is about all the Genesis carb has in common with other flat-slide carbs. The rest of the Genesis carb's throat area is a major departure from anything else on the market today. One glance into the carb's venturi will quickly show you why.

Unique Design
For starters, the throat of the Genesis carb is not the traditional spherical shape; instead, the bottom third is V-shaped with slightly radiused walls. The throat is five-axis CNC-machined with slight ribbing covering the entire 360-degree interior circumference. The ribs are designed to keep fuel in suspension while generating a boundary layer that can actually improve airflow.

Another unique feature of the Genesis carb are vortex generators machined into the bottom and top of the carb's throat. Small vortex generators at the bottom (one on the entry side, two on the exit) increase air velocity at low-throttle settings for improved fuel atomization and throttle response while large vortexes at the top (one each on the entry and exit sides) improve velocity at high-throttle settings. The combination of a V-shaped throat, vortexes, and rib walls provide maximum velocity at low speeds and maximum flow on the top end. The result is a carburetor providing the best of both worlds: Response of a 38mm carb at low throttle settings with flow greater than a 48mm at wide open.