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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).
Experiments to improve fuel distribution with a downdraught carburetter.

Identifier  ExFiles\Box 13\3\  03-page302
Date  2nd April 1931
  
To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey}
c. to Sg.{Arthur F. Sidgreaves - MD} Mor.
c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design}
c. to By.{R.W. Bailey - Chief Engineer}

X7080

Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey}1/KT.2.4.31.

X7080.
x5080.

DISTRIBUTION WITH DOWNDRAUGHT
CARBURETTER
-----------------------

As previously reported the distribution with the Downdraught carburetter, when bolted directly to the induction pipe is very poor and very critical to the throttle position. The first experiment to try and improve the distribution was to place an extension 1.500 in length between the carburetter and the induction pipe, this extension piece made no difference whatever to the distribution.

An aluminium washer with a bore of 2.000 (i.e. .250 less than the bore of the throttle body) was then placed between the induction pipe and the extension piece, this washer improved the full throttle distribution considerably, in fact to such an extent that we were able to run the engine at 500 r.p.m. full throttle quite steadily, previously we had never been able to at this speed steadily. This washer however did not improve the throttled distribution.

As an experiment we made an extension piece 6.5" long, but even with the throttle removed so far from the induction pipe the distribution was just as critical to the throttle position. The throttle appeared to throw the mixture on to the wall of the extension piece where it condensed and ran along the induction pipe and into the end cylinders. To prove this point we had a water heated hot-spot made round the extension piece and with this hot-spot the distribution was improved considerably. The distribution compared favourably with that of the standard carburetter and induction system, the full throttle distribution was exceptionally good and was equal to that of the standard system, on throttled positions conditions were also good there being only on position (about 5° from full throttle) where the distribution was at all critical, at this position the end cylinders were slightly richer than the centre ones. This scheme is not practicable as the carburetter is too high above the engine, the absolute maximum that the carburetter can be lifted and still be kept under the bonnet is 1.000".

The scheme we have on the carburetter at the moment is one in which a 2.000" dia. choke surrounds the original one (which has been shortened) and of such a length that it dips into the induction pipe .5000", by fitting this choke we have upset the metering considerably and the distribution does not appear to be much better than when the carburetter is bolted directly to the induction pipe. The type of pipe which may improve the cold distribution is one of the 'Weir' type and drawings for a pipe of this type have been made.

Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey}
  
  


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