Velocity stacks are used in top fuel bikes and dragsters. The idea came from Carl Morrow, who placed a small cup on the trailing edge of the stack. He discovered that he could increase air velocity by modifying carburetor setups. Stacks increase power and acceleration by a factor of two. In this article, we will explore both types. Listed below are the pros and cons of each.
Motorcycles with short velocity stacks provide the greatest boost potential. They allow the engine to reach higher RPMs for full throttle acceleration. A short velocity stack also helps with the upper RPM band and evens out 1/8 mile racing. Longer stacks can give the midrange punch, but the short-to-mid-length ratio gives the motorcycle better wide-open throttle performance. The short velocity stack offers a high midrange response, but lower low-rpm power.
The outer two motorcycle velocity stacks are susceptible to the effects of water running off the tank sides. To keep these out, you can place a squash ball or aerosol cap over the outer two stacks. But don’t let your excitement erupt. This is an important part of the performance. If you want to make the most out of your motorcycle, you have to tune the velocity stack so that it works the way it is intended.
In addition to adding horsepower, short motorcycle velocity stacks can improve the air flow through the engine. These components improve air flow to the throttle bodies. If used in conjunction with an aftermarket exhaust system or a PCIIIR, velocity stacks can increase horsepower. If used properly, however, they can boost horsepower without requiring any other modifications. It’s worth a shot. The benefits are clear, however:
The longer the velocity stack, the more horsepower and torque it will produce. The Meanies did not use velocity stacks for this reason, because the manufacturers were not required to include them. However, the longer the velocity stack, the less low end performance it will have. Kawasaki recently changed the design of their Ninja 1000 to improve low end performance. While this change is an improvement, it will not eliminate all of the benefits of the product.
Motorcycles have an intricate airbox and factory-geometry, which makes them ideal for these modifications. BMW has changed the airbox many times over the past decade, and now offers a racing-style airbox for bikes in the HP4 Race Series and WBSK series. These changes are geared more toward top-end use than midrange bikes. Long velocity stacks, on the other hand, are designed for race use.
The bell-mouth-shaped opening in long velocity stacks reduces the amount of turbulence associated with air moving through the interior surface. The bell-mouth shape allows air to flow more smoothly along the boundary layer, the transition between stagnant and flowing air molecules. Because there is less turbulence, the engine loses less kinetic energy, which means less horsepower at the rear wheel. Ultimately, the more horsepower a motorcycle has, the better it will perform.