What is Twin plenum?
To be more competitive on the track, Rover found the stock injection design to be somewhat lacking, and in order to pass homologation for racing they could only use parts actually fitted to the std. production vehicle so Rover ran a limited amount of Vitesses in production with this improved intake system for the EFI. The answer to your question is that although initially this system produces very little or no noticeable power gains, it does, however, lend itself to a higher state of tune than the stock single plenum system due to its ability to flow more air at higher RPM.
