Quoting John Vine: When I took my R400D (alloy plenum) to the two Steve's, Steve P commented that I'd be much better off with the plastic plenum set-up. He gave two reasons: (a) the mixture drawn through the plenum remains cooler (and thus denser, improving volumetric efficiency), and (b) a much smoother airflow. Judging by mic's comment, Mr P was correct!
JV
Yes John, Steve was telling me the same thing about the benefits of a plastic plenum for my R300.
Good luck with the build Tim and see you on a Taffia blat soon.
Jeremy South Wales