there are many vanagons running with hollow cats.
That by itself does no harm.
( if chunks of cat material went downstream into the muffler..........that
could cause problems of course )

a factor to consider ............a hollow can for a cat doesn't flow as well
as  a good cat, or a straight pipe in place of a cat.
don't tell anyone I said this ............but a slick thing to do is weld a
piece of straight pipe into a hollow cat.   Best flow, least restriction.
There's on size of EMT electrical conduit that fits perfectly - just weld it
inside at both ends.  I've never done this of course, just heard about it.

re 'puffing' from a muffler - the most fun one I ever saw would expand out
on the side as pressure built in it........then release..........looked like
the thing was alive and breathing.
it might be technically illegal to run without a cat, even if no emissions
testing are required on your year van in your state.
----- Original Message -----
From: "Jim Johnston" <inmytree1@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, October 14, 2008 6:06 AM
Subject: Running without a cat...?

> Hello all,
>
> Vehicle:  91 GL with 163,000+, manual
> Location: Wilmington, NC
>
> I'm trouble shooting a stumbling idle.  I think I've found my problem. I
> noticed the exhaust puffing and the muffler had some odd sounds coming
> from
> the muffler itself.  So I pulled the cat and muffler.  I only snapped two
> of
> the three bolts.  It turns out, my catalytic converter has nothing  left.
> It's completely empty.  The previous owner had a S & S Exhaust system put
> on
> a few months before my taking ownership 3+ years ago.  The cat has big
> dents
> in it.  My theory is this: when the shop put on the new Header and
> Muffler,
> they cleaned out the Catalytic Converter.  In NC, vehicles older than 1996
> do not require emissions testing.
>
> I started her up, while a bit loud, no more puff puff puff....
>
> Would running with an hollowed out cat lead to the muffler breaking down?
>
> Now I have to figure out if I have to buy a muffler from S & S or does a
> stock muffler bolt up to the system.
>
>
> Jim
> Wilmington, NC