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).
Comparative table of specifications between a 20 HP car and a Buick.
| Identifier | ExFiles\Box 124\3\ scan0136 | |
| Date | 1st March 1928 guessed | |
| DESCRIPTION OF DETAIL. 20 HP. RR. BUICK. Bore and stroke. 3 X 4 1/2 | 3 1/8 X 4 1/2 Displacement. 3132 | 3400 Average max. B.HP. 54 | 63 Compression ratio. 4.6 | 4.7 - 4.8 Car weight, closed Sedan. 33 cwts. | 33 cwts. Tyre dimensions. 31 X 6 | 31 X 5.25 Axle ratio. 4.55 | 5.1 MPH. at 1000 eng. r.p.m. 21 | 17.9 Tyre effective dia. 35 lbs/sq.in. 31.4" | 30.9" Steering turns full lock. 2.2. | 3.00 20 HP. closed RR. 33 cwts. 5630 Light six Buick sedan. 7,000 | ||