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).
Analysis of a light spring indicator card to deduce back pressure with the exhaust manifold on and off.
| Identifier | WestWitteringFiles\K\September1923\ Scan59 | |
| Date | 1st September 1923 guessed | |
| G.11. LIGHT SPRING CARD - FIRING. EXHAUST MANIFOLD ON AND OFF. From this, one would deduce that the bump as shewn on the standard indicator card is chiefly back pressure. Unfortunately, we have not one really good card with the exhaust manifold off, but as far as we can see the dotted curve represents it very well. This gives :- Pressure in cylinder when inlet opens - (a) Free exhaust 2 lbs. per sq.in. (b) Standard silencer 5 1/4 lbs. per. sq.in. Now the difference between the two power curves (free exhaust and silencer) at 2000 r.p.m. will show us whether the bump is worth worrying about as regards power. If a drop of more than half the pressure in the positive pressure bump when the inlet valve opens does not make an observable difference, then an effort to remove it entirely will not be worth while - from the point of view of power - for it is obviously not spoiling the charge drawn into the cylinder. ---------------------------- | ||