Any add a cat and custom muffler to lower "scent"
 

Don't get me wrong. The smell of my engine is the eau de toilette of owning an early car. I don't hate it but I was thinking I could make it so that the vehicle didn't smell like a carbureted car. I have a brand new in the box hi-flow cat. I was thinking of ditching my early muffler and instead having the heater boxes enter a single pipe, into the high flow cat and into a high flow muffler. I don't want any more sound and I think that would be the same as the stock muffler sound and no any more restrictive because they would both be hi-flow. A warmed up cat does wonders for that "old-car" smell out the tailpipe. Not a huge problem or that noticeable but it just struck me that it is entirely repairable.

I replaced my cat to reduce that "old-car" smell (just the stinking exhaust) It helped quite a bit but what really improved it was to get the O2 system working properly so the car was running at the correctl mixture. From your tag line, it sounds like you've got an earlier car (pre lambda system) Is it all tuned up?

mike
'81 SC

Yup carburetors tuned via O2 sensors! ;) That still doesn't mean the exhaust will smell pretty!

There have been quite a few threads discussing this very subject. Try a search for "adding a cat" or something similar.

Here's one: http://forums.pelicanparts.com/porsche-911-technical-forum/506256-adding-catalytic-converter.html