4-stroke carbon pipe design Q's

[George Kennie]

I have long anticipated that YS might someday surprise us with Desmodromic!

John Pavlick wrote:

> 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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