Power boost valveFSE boost valves
An FSE Power Boost Valve (PBV) replaces the standard fuel pressure regulator fitted to a fuel injected engine's fuel rail. The aim of the PBV  is to maintain the fuel pressure in the fuel rail as close to the design pressure as possible for optimum performance. When an engine is at constant revs the PBV will maintain the rail at the same pressure as a standard fuel pressure regulator (they come preset) but when there is a sudden demand for fuel when the accelerator is suddenly depressed that's when the PBV comes into its own, reacting 1.7 times faster than a standard pressure regulator.

Technical Details
The PBV is what is known as a back-pressure regulator i.e. it controls the pressure behind it - see picture below. You will see that the PBV is on the return pipe to the fuel tank and the fuel rail is 'upstream' of it. When there is a sudden demand for fuel as the fuel injectors fire more rapidly for acceleration the fuel pressure in the rail will drop as the fuel pump tries to keep up with demand. What the PBV does is react to pressure changes 1.7 times more rapidly than a standard regulator thus maintaining the pressure in the rail much better. This translates to a better throttle response and in some cars with 'flat spots' on acceleration it can be quite an improvement.

Fitment Hint
Make sure you fit the inlet and outlet pipes to the PBV the right way round. We fitted one to our Sierra 4x4 and had to really concentrate! We have had a couple of customers phoning back to say their engine won't run properly. FSE offered to test the PBV's but did point out that they had never seen one fail. On telling the customers this they tried again and found that, indeed, they had fitted the pipes the wrong way round.

Perfect Combustion
So, a PBV will not increase the overall power of your car and if you were to accelerate slowly a standard regulator would keep up as well as a PBV. However, for more sudden accelerator changes the PBV maintains the fuel pressure better and therefore keeps the air:fuel ratio as close to the perfect stoichiometric 14.7:1 as possible for complete, efficient combustion. So there will be a bit more power on more rapid throttle changes but not on a constant or slowly changing throttle.