4-stroke carbon pipe design Q's

[Bill Glaze]

Bob:
Exactly so.  You've just described how, at low r.p.m., the valve overlap 
actually hurts volumetric efficiency, by allowing some of the intake 
charge to escape back into the intake tract, and be contaminated by 
exhaust gasses.  This, in fact, can be seen as a "standoff" of fuel 
vapor above a carburetor intake, as the intake charge is forced out 
"backward" before being ingested.  With larger engines, you can actually 
"tune" the engine as to where you want the peak torque to be, by 
changing camshaft timing a few degrees.  (Be careful, though; you don't 
want the valves kissing the piston tops.)

Bill Glaze

Bob Richards wrote:

>Bill,
>
>Ok, if I understand you correctly, the low pressure
>helps suck in the new fuel/air mixture during the
>valve overlap.
>
>Come to think of it, isn't this similar to the way a
>pulse jet works?
>
>I guess any kind of backpressure would defeat or
>minimize the process, which I think is the case with
>our setups.
>
>Bob R.
>
>--- Bill Glaze <billglaze at triad.rr.com> wrote:
>  
>
>>Bob:
>>One small correction: the outgoing exhaust pulse,
>>which is under 
>>pressure, creates a small vacuum behind itself as it
>>escapes; this 
>>creates a low pressure area that helps draw the new
>>charge into the 
>>combustion chamber.  I've used a "tuned" exhaust on
>>engines as large as 
>>540 cu. in. The tuning takes a little time on the
>>race course, but it's 
>>really worth it.  It doesn't work quite the same
>>with a blown 
>>(supercharged) engine, because the blower pressure
>>masks the small (by 
>>comparison) vacuum behind the outgoing exhaust.
>>Bill Glaze
>>
>>    
>>
>
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