they regulate the air fuel mixture for when the pressure cant be adjusted, it is set to around 3 bar but at idle drops this by approx .5 bar so when on full ecceleration it raises the fuel pressure, making it run lean. the power boost valve allows this toi be regualted as it can adjust the the mixture etc.
thus better with high increases with CAI's and forced inductions etc. mods that would alter the air fuel mixture. (which u dont have)
so in lamens terms. it reduces the flat spots and the bad idling that occurs when the air fuel mixture is altered, and since the regulator is non adjustable this is were the power boost valve comes into it!
depending on the state of your engine etc.
as the mixture beign off etc can alter the co levels. thus why if you have the power boost valve in effect can adjust it so it not too lean etc getting the levels running kool!!
they are ok and sort the fuelling but dont make much power difference on the smaller engines as my ga16 didnt feel any more powerful but on My SR20 the pick up is well better and pulls harder and better thru the gears!
I used mine to get through MOT time. All I had to do was lean the car out to compensate for the overly rich ECU mapping. Sailed straight through with very low emissions. Expensive but beats faffing around with a stock manifold just to pass every year, even through the car is legal with one mid mounted cat.
helpful as lowrider said for manifold mot issues, and if you need to sort out a lean mixture if you have done tuning mods. but apart from that it only helps performance wise from a standing start when pedal to the metal. this is what the manufacturers website says anyway.