964 exhaust

[anonymous-user]

A recent service revealed that my cat converter was on its last legs. Do i replace the whole system, run a cat by-pass or replace the converter to keep it all original? ultimately, i dont want to be affecting my insurance policy and i'd rather not have to change my pipe pre mot so i guess im looking for my 'compliant' options! thoughts welcomed!

[Ian964]

If your 964 was registered before 1st Aug 1992, you're allowed higher emissions levels at MOT time and so can use a cat bypass without needing to change it. Otherwise you could pick up a used cat from a breakers or ebay, or spring for a new one or aftermarket sports cat (not cheap).

[leosayer]

A cat bypass is a relatively cheap, great sounding solution to your problem.

You won't fail the MOT on emmission or lack of cat unless there is something else wrong with your car.

[silver993tt]

leosayer said:

A cat bypass is a relatively cheap, great sounding solution to your problem.

You won't fail the MOT on emmission or lack of cat unless there is something else wrong with your car.

Like being too noisy??

[wildoliver]

You can fit a decat as mentioned if yours is a 90 or 91 car, you can probably get away with it on a 92 car too as I know mine runs pretty clean.

I don't think there is any increase in noise, and certainly no noticeable improvement in power, I got a mild steel one off ebay for about £40, been on a couple of years and still fine, but I do advise getting one with a lambda probe hole.

[pope]

I have a Cat bypass pipe for sale!!

It hasn't got an O2 sensor hole - it doesn't need it if not running the Cat, it comes with the official sensor bridge plug too, so the DME will work fine with the Cat removed. Noise is not increased too much.

Used, 100% usuable. £60 with the skid plate, fitting olive and clamps.

[Lewy]

I've heard different opinions as to whether tha lamda sensor can be bridged when removing the cat.
I'm looking at removing mine soon but i fear that the sensor will break when trying to remove it.
Pope - Did you run yours with the sensor bridged ?

[wildoliver]

They do remove pretty easily, the secret is a very good fitting spanner, try it with a loose one and you will destroy the sensor.

It is my belief it should be used, it is there for a reason after all.

[pope]

The Cat bypass was an official tequipment part, the bridge was part of the kit, sanctioned by Porsche. The DME receives a base setting via the bridging of the sensor wiring fixing the mixture adaption at mid point. The car will run as normal.

Edited by pope on Tuesday 17th April 13:58

[anonymous-user]

Stupid question but I take it the bypass replaces the cat so you need to take the cat out of the system and replace it with the bypass pipe?

[computamedic]

ravi944 said:

Stupid question but I take it the bypass replaces the cat so you need to take the cat out of the system and replace it with the bypass pipe?

Correct. BTW removing the O2 sensor and jumpering the DME is not a great solution although it is workable. The O2 input into the DME allows it to continuously adjust the fuelling to achieve the optimum air/fuel ratio (14.7:1 I believe). Without the O2 sensor fitted the air/fuel ratio is fixed at a default level by the DME which may or may not be optimum for the conditions at the time. Most cat bypass units have the fitment for the O2 sensor but some do not.

Regards

Dave

[anonymous-user]

computamedic said:

ravi944 said:

Stupid question but I take it the bypass replaces the cat so you need to take the cat out of the system and replace it with the bypass pipe?

Correct. BTW removing the O2 sensor and jumpering the DME is not a great solution although it is workable. The O2 input into the DME allows it to continuously adjust the fuelling to achieve the optimum air/fuel ratio (14.7:1 I believe). Without the O2 sensor fitted the air/fuel ratio is fixed at a default level by the DME which may or may not be optimum for the conditions at the time. Most cat bypass units have the fitment for the O2 sensor but some do not.

Regards

Dave

Thanks Dave. What would be your recommended course of action?

[Lewy]

I've just removed my cat and fitted a Milltek bypass that comes with fixings to refit the heat shields. From what i have read on Rennlist, people prefer to fit a bypass with a O2 sensor and you can pick these up on e-bay for about £40. My sensor was a pig to remonve as the threads on the cat O2 socket had corroded to the sensor. Did manage to cut it out so i could re-use it though.
The engine note is a little louder especially as i have the secondary bypass fitted.