Some late model Subaru engines have tumbler valves in the induction manifolds. At idle the tumbler valves close to create a higher speed air flow over the injectors. This helps atomise the fuel better, resulting in better running when cold and lower emissions (see http://www.drive.subaru.com/Win03_Manifold.htm for more info on tumbler valves). However, the tumbler valves present a problem if you want to convert an engine with them to to multi point LPG injection. The position and design of the tumbler valves means there is no space to inject the LPG into the fast jet of air at idle. Adding aluminium plates between the cylinder heads and manifold allows the LPG injector nozzles to be positioned directly below the petrol injectors. The plates are water jet cut from aluminium plate (to order).