RE: Welcome to Club SAITO !
KH:
Strictly speaking, we're not talking about velocity stacks. A true velocity stack is part of a tuned intake tract, all we have are extensions to the intake ducting.
These stacks work to good effect on all engines, not just two or four stroke. I'm sure you've noticed the fuel spraying back out of the intake, the stack keeps most of that fuel in the airflow, it's drawn back in on the next intake cycle. The result is better fuel economy, and less fuel sprayed around inside the cowling. The best of all is a stack with an air filter.
Bill.