Like cheezels I run CEM products ! both their CRM and especially their FTC decarboniser. The FTC for me is a must, as it's stops the build up of carbon especially in the turbos, where a build up of carbon starts on the outer edges of the turbine blades . After looking at pictures of TdV8 blown turbos all seem to have had heavier carbon deposits on the outer turbine edges (centrifugal force), my uneducated guess is that balance of the turbine is effected, loading up the bearing, My theory anyway