Question : I READ with incredulity your answer
to the pipe size query in Auto Care of
The subject came up last December
and the answer then contained the
blunder that when the exhaust valve
opens, the inlet valve is still open.
I wrote about this on Dec 31 2007 which, contrary to all my previous comments, you chose to ignore.
Now, in the recent answer, the same
blunder is made.
If the inlet valve would still be open
when the exhaust valve opens, there
would not have been a compression
and power stroke; hence no need for
any combustion gases to be exhausted.
The opposite is true - when the inlet
valve opens, the exhaust valve is still
I think your answer in these cases is
wrong and must be confusing to many
Answer : I stand corrected. Somehow between thinking out the
answer and typing it out, the facts got jumbled. What I was trying to say
was that while the exhaust valve is open and the exhaust gases are flowing out, the inlet starts to open before the
piston gets to top dead centre and if the
exhaust system is designed correctly, the
exhaust gases will be extracted out.
However, before too much of the inlet
mixture goes out of the exhaust a positive
wave will return to stop it, and together
with the movement of the piston down-
ward the inertia of the mixture coming in
will maximise the inlet charge.
If the exhaust system is not designed
correctly, the pressure waves will come at
the wrong time and instead of improving
performance, the performance will drop.