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).
Test report on modifications to a Large Phantom II expanding carburetter to reduce induction pipe depression.
| Identifier | ExFiles\Box 13\4\ 04-page134 | |
| Date | 20th March 1933 | |
| To E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell} c. to Ey. LARGE PHANTOM II EXPANDING CARBURETTER LEC.3137. Tests have been carried out with the object of reducing the induction pipe depression from its present figure of 2.5 Ins.Hg. at 3000 R.P.M. By the following alterations to the existing carburetter the depression has been reduced to 2.0 Ins.Hg. at 3000 R.P.M. (a) Increased air valve inlet from 2.375 dia. to 2.75 dia. (2.25 Ins.Hg.) If the original piston (E.83354) be run in conjunction with the larger inlet, the distribution is good an unaffected. By screwing a flat disc 2.9 dia. to the original piston diaphragm 2.6 dia. in order to seat above the increased 2.75 dia. port, the distribution is affected with the rear cylinders rich. This indicates that the air flow is deflected by the larger diaphragm which is in too close a proximity to the large choke formed by the throttle body. Any increased diaphragm should therefore be accompanied by an equivalent increase in centres between the air valve and the throttle body. If the larger air valve be used, it is possible to obtain the desired movement by taking the suction past the piston clearance, without the necessity of using a fixed hole for this purpose. For test purposes it was found that a 2.900 dia. disc screwed to the original piston gave a satisfactory movement. (b) Throttle body increased from 2.25 dia. to 2.375 dia. with tapered hot spot to suit (2.1 Ins.Hg.) (c) Intake flange extended to centre line of throttle body and air valve (2.00 Ins.Hg.) Up to this position the distribution remained good, but if continued round to the floatchamber as shown (D) in (V.1530), the rear cylinders run rich with the front cylinders weak. The proposed modification to the intake flange is shown on V1529. | ||