Cat reduction

[timb2117]

Hi just looking into exhaust modification as mine has cracked twice in 2 track days and at 15 years is probably a tad past it. K series 1800.

I notice a lot of people do the cat removal route however note that power gains are not huge and at $10k fine I don't fancy playing...

I can get a 200 cell high flow cat which should be approx half the restriction of the 400 fitted by manufacturer. Has anyone any experience of this good / bad or indifferent?

 I am keen to get a slightly better noise and good flow but dont want to send the computer haywire, it has a pre and post o2 sensor as standard.

[SM25T]

Where does it crack. Front of can where inlet pipe enters ? Are you using the centre support bracket on the exhaust ... if not it is sagging between rear mount and attachment to the cylinder head. I had this and opening up the centre mount and fitting a support cured it.

[timb2117]

The first time was where the 2 go into one with the lambda sensor hole being the weak start of the crack (which I suspect had been blowing for a while)

 Second one was actually the rear bracket that holds onto the cotton reel rubber mount and the thing there was it opened up the rear silencer box slightly and I noted the silencer wall was paper thin - possibly from age and wear. 

Certainly will consider a centre support as it is a long run of pipe/ silencer/ cat to hang off the block to the back mount.

[Wrightpayne]

I always fit the complete exhaust loose before fully tightening all the fixings including the manifold nuts. It is easy to induce stresses and I feel this approach lets the system 'hang' naturally IYSWIM.

 

[sylvaman]

Interesting , what you said about sending the computer haywire; when running without a cat.

  Is this general or more aimed at  K series ? 

[simon_h]

I’d hazard a guess he has a eu3 K series in Europe which carried over the catalyst monitor diagnostics from the rover donor. It will put on a MIL if it doesn’t see the cat. Mind you generally after a short time cars do with 200 cell cats as well as they aren’t very efficient 

[timb2117]

Yes Simon you are correct however I have the furfy that I am in Australia and we are not exactly renowned for fuel quality, I run it on 98 octane which is the best available.

Forgive my ignorance "a MIL"? There are two sensors one pre cat and one post cat so I simply figured the second one if it detects incorrect cat function or no cat at all  would 'report it" to the main computer.

I will follow your good advice about letting it settle into position before syncing up. My friend is going to build it with V clamps his quote was that "if they're good enough for the atomic bomb...."

[simon_h]

MIL, check engine light etc. Not sure if they had that fitted back then as they do with the current eu spec cars. It shouldn’t actually do anything if it detected the cat has failed, just flag a fault code from memory

[timb2117]

Brilliant thanks Simon, 200 cell cat it is then.