Was asked for more:
The shock in a pipe occurs at the end. The pressure
wave in reflection turns negative instead of positive.
The low pressure local eddys will cause some residual
exhaust to be drawn out of the combustion chamber.
The effect and geometry is determined by the local
speed of sound in the duct. It is the suction caused
by the shock that gives you the advantage. This is why
stepped headers are allegedly so effective - the
designers tune the steps so the shocks occur at the
right time to maximize scavenge effect.
--- Ron Soave <soavero@yahoo.com> wrote:
> > If the pipe is to small it restricts the
> > flow of the pulse (slowing it down).
>
> Velocity = flow/(density * area)
>
> For a given flow rate, a smaller diameter yields
> higher velocity. But the flow is not going to be
> constant - with increased backpressure, there will
> be
> less flow. It just isn't that simple. Sonic
> velocities are important to the scavenge effect, and
> the timing of the shock associated with expansion of
> the exhaust gas.
>
>
> If the pipe is
> > to large the pressure of the pusle dissipates
> > and there is no scavanging. I would suspect the
> > stock exhaust size is pretty close to correct
> > as the original engineers knew about this issue.
> > They did make compromises in the exhuast manifold
> > (for cost, longevity, etc.) so a set of headers
> will
> > help performance.
> >
>
>
> =====
> Ron Soave
> "You Are What You Remember"
> 1960 Bugeye
> 1972 BGT
> __________________________________________________
> Do You Yahoo!?
> Bid and sell for free at http://auctions.yahoo.com
>
=====
Ron Soave
"You Are What You Remember"
1960 Bugeye
1972 BGT
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