After a fair bit of pondering and a few false starts I have decided to go back to a modified version of the original PI air plenum on my white PI.
A study of the ram tubes internal to the Triumph part says they are identical in profile to 45 DCOE weber ram tubes. The arrangement certainly facilitates easier introduction of cold air and the main issue seems to be the lack of overall diameter meaning cylinders 4-5-6 may be progressively starved of air in extreme conditions.
I have started to trial fabricate an alloy air box around the intake and intend to enlarge the inlet end of the plenum to maybe 110mm up from the current 84mm
Another thing on the list before I fit the new 2100 engine to my everyday saloon was to get the new 6-3-1 fittted with O2 sensor and collector properly fabricated with the 2" Witor system.
I will need to drive the car without a collector or silencer fitted to the local exhaust fabricator to get the collector finished and the Witor 2" sport system fitted.I didn't want to drive the new engine unsilenced and not have good mixture control due to lack of wideband sensor with the new engine so this needed doing before the main swap.
I removed the old exhaust and the witor SS 6-3-1 for resale in a couple of hours and was pleased with the fit of the Gareth Thomas manufactured 6-3-1. I was also glad that I made the effort to make the inlet manifold one piece with detachable loom as it made the whole swap very quick.
Back together and running (loudly) in less than 3 hours