Here's a good read with pics on a tuned system.

http://www.thesamba.com/vw/forum/viewtopic.php?t=270833&highlight=exhaust

On Sat, Feb 13, 2010 at 10:36 PM, Kim Springer <kimspringer@astound.net>wrote:

> Hey listers,
>
>
>
> Has anyone ever measured up a stock exhaust system to see where it's
> designed to make HP. I assume VW did this a long time ago.
>
>
>
> I guess another way to ask this question is: Did the folks making SS
> exhaust
> systems in a 4-2-1 or 4-1 design improve on what VW designed?
>
>
>
> I have a book that helps to design 4-Stroke intake and exhaust system
> lengths, inner pipe diameters, etc.
>
>
>
> All this talk about hollow cats makes me wonder about the secondary pipe
> length. Not that anyone is going to gain 10 HP out of this.just wondering.
>
>
>
> Kim
>
> 88 Tristar #7 (it's either going to get painted or sold in the next year)
>