Put that semester to work and make / design plans for real performance Virago exhaust. I think most are just make to fit in stock location or use stock parts with no real concerns for performance.
> Waver length tuning is simple on a 4 stroke, but in a 2 stroke back pressure
> comes into play. That is why the large diameter pipe works so well in a 2
> stroke for low rpm torque and has the opposite effect in a 4 stroke. The loss
> of back pressure at low rpm allows the cylinder on a 2 stroke to get rid of
> spent gas faster, to the point that a lot of unburnt gas goes out the pipe. The
> object is not fuel efficiency here, only low end power. On a 4 stroke the loss
> of back pressure gives more high rpm torque, but wave length comes into play
> because of complex valve timing issues. That is when you see the "bowl of
> spaghetti" exhaust systems on formula racers. I am being simplistic here for
> the sake of discussion. I spent a whole semester at college in a class studying
> only exhaust and intake systems.
>
> Al Hatten
> '93 Virago XV-1100
> VOC #7745
> Napa,CA - Wine Country
>
>
> On Sun, 30 May 2004 00:12:16 -0400, Douglas W. St.Clair wrote:
> > On 5/29/04 3:19 PM, "Al Hatten" <alhatten@xxxxxxxxxxxxxx>
> > wrote:
> >
> >
> > Al, good observation, you are right in what you saw, but
> > you misunderstood what you were seeing. Actually the
> > phenomena is not at 2-stroke thing it is the result of
> > 'tuning' the exhaust and it isn't a function of pipe
> > diameter but effective length. Here is how it works.
> > First a rule: When a wave meets a change in the medium it
> > is traveling in some is reflected. Consider the obvious
> > case of a sound wave traveling from the source and
> > hitting a wall. The medium is air and then the medium is
> > plaster. When its hits the wall some is reflected and
> > some goes into the plaster. The simplest case is a
> > straight pipe with no muffler or anything between the
> > valve and the end of the pipe. When the exhaust valve
> > opens the cylinder dumps hot air into the exhaust
> > manifold. The pressure leaving the cylinder is higher
> > than ambient air pressure (positive). When the pulse
> > reaches the end of a straight pipe the medium changes
> > from a restricted pipe to the open atmosphere and some of
> > the energy bounces back down the pipe toward the valve.
> > Behind this positive pulse is a negative pulse. If you
> > run the engine at the right speed you can get positive
> > pulses arriving at the open valve and the engine doesn't
> > scavenge very well and HP drops. At a different RPM the
> > negative pulse will arrive just as the valve opens and
> > the cylinder will scavenger better than it would into
> > ambient pressure and HP increases. The shorter the pipe
> > the higher the RPMs at which 'tuning' occurs. A flare in
> > the pipe flattens or widens the power band which is very
> > narrow with simple straight pipe.
> >
> > Surprisingly it takes a lot of work to develop and intake
> > and exhaust system that doesn't tune and provides at wide
> > power band.
> >
> > If you want to make a screamer you can take an engine,
> > tune it for a very narrow power band, and put a 50 speed
> > transmission on the vehicle so you can drive it at more
> > than one speed. <g>
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