"Chris Bacon" wrote in message
...
Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Dave Plowman wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.
[CPB disagreed]
Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and
others).

Above is what DP says determines the CR. Do you *really* agree, or
can you add something to that statement to make it right?


Where does volumetric efficiency come into this, do you think?

It's got nothing to do with the compression ratio. (I may stand
corrected).

As it's [CR] normally measured, nothing. It was un harang rouge.


I used to own a BSA Blue Star 350cc OHV _single_ cylinder 1934
motorcycle. This bike had _twin_ exhaust ports and exhaust systems. The
only reason for this, in my opinion, must have been an improved
volumetric efficiency ( the single inlet and single exhaust cylinder head
valves were the same size).

At higher RPM, having twin exhaust valves is an improvement over one,
cetrainly. This is reflected in ancient engines which were constructed
with performance in mind, as well as modern ones.


However, tuning the
exhaust system gives lesser results in comparison with the effects of
tuning the input system (by quite a lot)

I believe that 2 stroke (racing?) engines were greatly improved (over a
narrow revolutions band) by tuning the exhaust.

Sylvain.