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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 efficiency of American car engines and the need to test exhaust system losses.

Identifier  ExFiles\Box 134\2\  scan0111
Date  31th May 1937
  
Sg.{Arthur F. Sidgreaves - MD} from Rm.{William Robotham - Chief Engineer}
Hs.{Lord Ernest Hives - Chair}
c. E.{Mr Elliott - Chief Engineer}
c. By.{R.W. Bailey - Chief Engineer}

Rm{William Robotham - Chief Engineer}17/H.31.5.37.

EFFICIENCY OF AMERICAN
CAR ENGINES.

We obtained a lot of American power curves while in America. We were able to get cross checks from the Companies themselves, from General Motors, and from some of the Carburetter Laboratories where they had these engines running. We attach a summary of some of the results.

The outstanding point is that our losses to the exhaust system are high, and when we have actually got the engine installed in the car we cannot claim to be superior in power output to the average American engine, particularly over the range used 80% of the time by the customer. The 25/30 shows up badly in this respect (curve 6).

One of the things we propose to do, therefore, as soon as possible, is to check the losses to the exhaust system of some of these American cars, and try and reproduce their results. This can be done on the new test bed.

We have been in the habit of considering open exhaust figures too much on our engines. It is no good having good top horse power if 90% of it is to be dissipated in burning out the exhaust system.

The overhead camshaft engine has proved to be disappointing under installed conditions. It is sensitive to exhaust back pressure - it has not lived up to its freedom from detonation on the Test Bed. So far its road performance does not justify the additional complication incurred. We are going ahead, however, to get all the information we can before finally condemning it.

This experiment has demonstrated the value of having a 'mock-up' engine. A side-by-side test on the road at equal weights with a standard car is worth more than all the power curves ever drawn. We think it imperative that we should have a 'mock-up' of the overhead
  
  


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