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).
Comparison of performance between improved bakelite, 40/50, and stabalite ignition coils.
| Identifier | WestWitteringFiles\J\December1922\ Scan86 | |
| Date | 14th December 1922 | |
| Contd. -4- Improved bakelite coil as above described on cylinder head 40/50 coil on cylinder head .035 (average of 2 comparisons on different days). In this condition the improved bakelite coil is easily made to miss by touching the outside of the coil case when distinct leakage can be felt, where no effect is produced by touching the 40/50 coil. As regards the 40/50 stabalite coil, this appears for some unknown reason not to stand such a large external gap when running cold as when hot, especially at slow speeds, though the margin of perfomance is satisfactory. also a 40/50 coil misses at high speeds with an additional external gap exceeding .030". Another test on the improved bakelite coil showed that the maximum allowable gap when hot (uninsulated) running slow on the road, and picking up with weak mixture and retarded ignition was .025". With this gap there is no missing across the gap itself, but on picking up the spark is not so strong as on the 40/50 coil. The engine does not get away so well and appears to feel the effect of the weak mixture more than when running under the same conditions with a 40/50 coil. A very slight leakage can be felt on this gap, but not enough to cause misfiring when the coil case is touched. EFC. | ||