4-stroke carbon pipe design Q's

[John Pavlick]

Bob,
 If you want to be scientific, remember, in science nothing "sucks". It
"blows"! The atmospheric pressure pushes (blows) the charge in. Since the
pressure differential is greater during overlap you get a scavenging effect.
What Bill's talking about is "the fifth cycle". Every good tuner knows about
this. Since overlap is good you might think that more is better. Not really.
The downside to too much overlap is less torque at lower RPMs. Also, with a
lot of overlap, you may see fuel coming out of the carb. at idle with a
restrictive exhaust. There are a lot of tradeoffs but a well tuned system
makes more power in a given RPM range than a simple muffler.
 What would be really cool to see is roller tappets. The trick with a 4
stroke is to maximize the charge going into and out of the cylinder, while
maintaining compression. A roller tappet / cam maximizes the area under the
curve because the tappet can lift faster and with less tendency to float
because you can use stiffer valve springs. They also reduce friction (heat).
Roller tappets are a good thing. It would be a challenge to make a roller
cam setup for our little motors but it would proabably make a lot of power
and smoothen the idle a little too. Almost all modern high performance
motors run roller cams.

John Pavlick
http://www.idseng.com


> -----Original Message-----
> From: discussion-request at nsrca.org
> [mailto:discussion-request at nsrca.org]On Behalf Of Bob Richards
> Sent: Monday, May 23, 2005 9:48 PM
> To: discussion at nsrca.org
> Subject: Re: 4-stroke carbon pipe design Q's
>
>
> 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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