Could someone please tell me what velocity stacks are and what they actually do? Also are they safe for street riding or just a competition mod? And finally are the ones sold from the kawasaki website any good? Thanks a bunch for the help.
Velocity stacks are an old idea, almost as old as the carb itself.
If you pull off the top of your airbox you'll see four bell-mouth shape tubes pointing upward. Those are the volicity stacks. Ideally the two in the middle of the airbox should be a little taller than the ones on the outside. If you understand fluid dynamics - which I don't - the premise is that all four cylinders will get the same amount of air, both in density and velocity, at the same time.
Since the distance to the bell mouths of the outer pair is further from the intake than the middle pair you need to make the two stacks in the middle longer. This way the air has to travel a slightly longer distance before it reaches the combustion chamber.
The end result is improved mid-range and top-end power. While not everyone will notice that improvement, I know for fact that it does improve throttle reponse noticalbly.
This is an over simplification, but a short velocity stack generally produces top end power, where a longer stack produces more torque. The physics include the velocity of the intake air, the mass of the intake air, and so on. Short stack produces good velocity at high RPM, while a longer stack (more mass within the intake) produces better filling at a lower RPM. You can tailor your power depending upon the need by changing the velocity stack length.
My guess would be the stock stacks sacrifice a little top end for mid range, and the racing stacks are tuner for top end power. This is a guess, since I don't know the actual configuration.
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