When using another exhaust pipe, it will influence the opening of the power valve. With the VHM power valve adjuster with 2 stage spring, you are able to adjust the opening timing of the powervalve easily with the screw. The first stage of the spring allows the powervalve to open very easily for a better and direct response. The second part of the spring keeps the powervalve fully open for a maximum exhaust flow. The VHM powervalve adjuster is made from high quality aluminium.