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).
Technical letter discussing camshaft timing and engine performance for Bensport and Peregrine models.
| Identifier | ExFiles\Box 179b\1\ img274 | |
| Date | 23th January 1933 | |
| HS.{Lord Ernest Hives - Chair} ) FROM R.{Sir Henry Royce} E.{Mr Elliott - Chief Engineer} ) [Text crossed out: G.{Mr Griffiths - Chief Accountant / Mr Gnapp} to Sur. MCR. RG.{Mr Rowledge} WY] R3/M1/1.33. Sent off 23.1.33. BENSPORT. X45533 I am very pleased to hear that you are getting on so well with Bensport power unit, (and the car also, which has been fun and given much satisfaction to HS.{Lord Ernest Hives - Chair} and RM.{William Robotham - Chief Engineer}) The new timing of the camshaft is what we have been trying to get for a considerable time, but we were told it caused falling off in low speed torque. Personally I did not mind this as I thought it was beneficial to detonations which regulated the limit of the compression ratio. This timing had its essential feature of a rather later opening exhaust, approx: 45°, and a rather later closing inlet, about 60° (.020 clearance.) The amount of overlap was to be regulated by the slow running, and the noise of the suction. All this now seems to have been made satisfactory. These figures generally represent a camshaft of about 114° instead of approx: 110° at present in use. I mention this especially with a view that we shall be able to use much the same timing on our little Peregrine, J.{Mr Johnson W.M.} 3., and 45HP. The other feature which seems to have done good is the increased clearance around the inlet valve. This we have always tried to do to the extent of the space available, and I fear we may be now doing this at the risk of getting a thin place. I hope however there is sufficient metal left. This is also another feature which might be carried out to some advantage on the other engines. It may have some slight advantage on the turbulence, inasmuch as the average flow of air would be a little further from the centre of the cylinder bore, and therefore increase the vertical swirl. I quite agree that for ordinary standard the Bensport model will rarely be run at engine speeds of 4500, but more often at about 3000, and it is very desirable not to overgear the car except if we find that the engine will not stand extra revs., or be irritatingly fussy, then probably we should have to put another tooth in the back axle pinion. That we lose a little HP. at 1500 to 2000 RPM. in this or Peregrine would make hardly any difference. I understand now that the first Bensport has not a separate gearbox, so will be somewhat cramped for foot room at the pedals, but this will be cured with its own gearbox and flywheel. R.{Sir Henry Royce} | ||