pcarrera993

on my car I have what looks to be two exhaust cat bypass boxes. they are located immediately after the headers and before factory cats. According to Adrian Streather's 993 book there are cat bypass available from Porsche dealer. Does anyone have more information on this and can help me identify? I will try to post pictures this weekend but if someone has a picture of what one looks like please post.

Thanks,
--T

Bill Verburg

this is a stock US '96 up 993 exhaust


RoW and '95 US would just have 1 O sensor centrally located the cat. between the 2 inlets other waise would be the same

ReinerFink

That pict is in need of some Xenit!

-reiner

pcarrera993

Thank you, this is very helpful. I will cross reference with my car.

trophy

There are alot of options other than porsche for Cat-Bypass pipes (I didn't know they had them, probable ROW type part): FabSpeed, Dach etc. Prices start at $500.

pcarrera993

how does the valve on the stock bypass work? does it dump out at certain rpm?

trophy

There are no valves in the 993 system, it is continuous flow stock.

trophy

Here are the parts as per the diagram Bill posted.

Red - Headers / Heat Exchangers
Green - Cats
Blue - Mufflers / tips

Garth S

I'm guessing that you are looking at the two rectangular 'boxes' that lie inboard of the heat exchanger shrouds as shown in Bill's pic.

These units have flap valves that admit ambient air to balance pressure .... and therefore flow to allow the HVAC system to draw hot air into the cabin - from the external side of the headers..

No active control on these flap valves, no connection to the exhaust system: they admit ambient air to the headers external heat exchanger chamber

....... if that's what you were looking at .... if not, I'm as curious as anyone else ....

Bill Verburg

here is a full header setup w/ aftermarket cats and mufflers


and here is an aftermarket cat by pass w/ stock mufflers

pcarrera993

That is exactly what i was curious about. I was under the impression it was a waste gate of some sort but on the contrary as you point it allows ambient air in. Thanks!

Bill Verburg

, actually out, the dumps are connected to the heating system via the orange sleeves. When you call for heat in the cabin they are closed, when the heat is off the heated air is dumped into the slip stream under the car.

pcarrera993

yeah the way the valves are pointed towards the rear originally led me to believe it was an outlet. This makes total sense now. Thanks for the insight. Introduction is way due and I will as soon as I can download pictures. Im old to the passion and just recently bought my first 993. eager to learn as much about my car as possible. This is a great place!