There is no venturi, nor is there any claim of a ventri in this pipe.
I seriously doubt it has much if any power over a standard pipe. I think it may even make less power than a standard pipe, but this is just my opinion. It would take a side by side dyno comparison to know for sure. Chamber type of technology is normally associated with a 2 stroke.
From FMF website:
The redesigned PowerBomb is a four-stroke header that incorporates FMF’s patented PowerBomb module at a precise location in the initial stage of the header. By positioning this “Bomb” at a key point in the system, increased performance and flow is achieved through the expansion and contraction of exhaust sonics through the system. Result is a flow increase of nearly 10%! The outer chamber in the Powerbomb allows the air to expand, cool and ramp back up at a higher velocity.
Additionally, the PowerBomb is a “pre-muffler” of sorts which helps to lower the bikes sound output by providing more sound absorbing surface area for the sound medium (exhaust gases). On some models, you can choose between a moto or supercross version. The supercross version is designed for more low to mid-range power where the moto version is focused in the mid to upper RPM range.