Well said Martin.  I might add that if one has to design an exhaust system,
Phillip Smith's "The Scientific Design of Exhaust and Intake Systems" will be
an invaluable reference.  If you gotta build one, you might as well build a
'correct' one.

BTW, Distributed by Classic Motorbooks.  Amazon probably has it.

Jim
[...]
Martin Jagersand wrote:
>
> Exhaust systems are designed with many considerations in mind.
> Other than the average flow (DC component) there is a significant
> pulsating (AC) component. Lengths of tubing acts equivalent to
> inductors, cavities like capacitors, and the combinations like
> filters. And there is always a resistive component...
>
> Study the layout of the VW car exhausts: First a length of tubing
> then a resonator, then another length of tubing, then a muffler
> and tailpipe. This is equivalent to two low pass filters in series.
> The objective should be to copy one or both of these.
>
> Practiacally on the vanagon it's possible to match the first
> length to the resonator and then put on the muffler. For some
> layout ideas see the pictures on:
>
>   http://www.cs.jhu.edu/~jager/vw/engine/Diesel1_9swap/
>
> If one wants to put in both components the exhaust would first
> have to be routed under the mid section of the van, then a resonator
> then a go back towards the rear, rear muffler etc.
>
> For performance (best scavenging) it is most important to match the
> first length of tubing after the engine.
>
> Good luck,
> Martin