From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Graph comparing engine performance with 1 3/4 inch and 1 1/2 inch diameter chokes under various conditions.
| Identifier | ExFiles\Box 19\1\ Scan125 | |
| Date | 23th March 1931 | |
| Pt UNIT B.J.55, FOR 27 EX RM{William Robotham - Chief Engineer} P26 COMPARISON OF 1 3/4 AND 1 1/2 CHOKES 114° E 82448 CAMSHAFT R.R. TWIN CARBS. 4-88 C/R OPEN EXHAUST STANDARD ROCKERS ① ----- 1 3/4" DIA CHOKES ② -- -- -- 1 1/2" DIA CHOKES ③ ...... As 2 BUT WITH AIR SILENCER B.H.P R.P.M INDUCTION DEPN INS. HG. B.M.E.P. LBS/SQ" EX IN 60 56.5 27 12.7 013 CLCE | ||