The benefits of de-Catting, or not !!

[hughesie2]

Over to the technical massive.

We have a 320 SLK that has rattly cats;
Rather than replace them i thought of getting them removed or replaced with a Sports zorst

A) what are the benefits of De-catting
B) Can you de-cat a 3.2 V6 MB engine ??
c) Does the ECU need re-programming to accomadate the extra flow etc etc etc ??
D) who can i get a sports zorst from ??

Have traweled the net to no avail, any help appreciated !

[Tony427]

I had a Mondeo V6 with a rattly middle cat,they had two small cats at the manifolds and a bigger central one under the floor. So I removed said rattly cat and using a long piece of steel and hammer removed the ceramic innards in small pieces. This left an empty casing which I refitted. Result was a significant increase in power, a better exhaust noise and the car even passed the MOT emmisions test.

I have also removed the cats from a BMW V8 I have in my Cobra without any detremental effects on the engine. Once again the engine note has changed from a soft burbling rumble to a rasping aggressive bark especially when "pressing on" . I am told that I should have gained 30 bhp as a result btw.


If the cats are rattly you will lose nothing by taking the innards out and giving it a shot, the worst you can do is gain about 20+ bhp.

Cheers,

Tony

[Hughesie2]

Cheers !!

[dern]

Tony427 said:

I had a Mondeo V6 with a rattly middle cat,they had two small cats at the manifolds and a bigger central one under the floor. So I removed said rattly cat and using a long piece of steel and hammer removed the ceramic innards in small pieces. This left an empty casing which I refitted. Result was a significant increase in power, a better exhaust noise and the car even passed the MOT emmisions test.

That's the job for this w/e sorted then

[Hughesie2]

dern said:

That's the job for this w/e sorted then

Snap !!

[boosted ls1]

My saab was left trailing Audi TT's until I got rid of the blocked cat. Now I can reel them in

The cat must sap a lot of power unless mine was really blocked up. The car had 277'000 on the clock so it's nearly run in now

Boosted.

[campbell]

boosted ls1 said:

My saab was left trailing Audi TT's until I got rid of the blocked cat. Now I can reel them in The cat must sap a lot of power unless mine was really blocked up. The car had 277'000 on the clock so it's nearly run in now Boosted.

Just like a Volvo if i can say it


Ill get mee coat

[boosted ls1]

Don't forget your hat and shut the door on your way out!

Boosted

[nel]

Am always a bit bemused by this issue. Presumably completely de-catted beasts have to have the cats stuck on again every year for MOT purposes? Does it not worry the engine's brain, e.g. lambda sensors and all that?

[DeltaFox]

nel said:

Am always a bit bemused by this issue. Presumably completely de-catted beasts have to have the cats stuck on again every year for MOT purposes? Does it not worry the engine's brain, e.g. lambda sensors and all that?

Anything after K reg should have a cat on for Mot purposes.
As regards the ecu's ikkle brain it never gets to "see" the results of a cat removal as the O2 sensor is upstream of the cat usually, so its removal isnt needed to be factored into the equation.
Noticed an immediate difference on the 4 when the cat was removed even though it wasnt blocked or rattly.
hth.

[Andy_CTR]

I've fitted a race manifold to my car, which replaces the cat completely. Those talking about an increase in noise are spot on - mine sounds viscious when giving it full beans !! The increase in performance is significant as well.

A word of caution though, I was finding that my a/f ratio was well out, so needed to map the car properly to avoid running too lean.

With regard to sensors - my car has two - 1 either side of the cat. Before I upgraded my ECU, I was getting a check engine light on the dash, as the car was correctly recognising that the cat wasn't doing it's job properly - good diagnosis as it was in a box in the garage

[boosted ls1]

DeltaFox said:

nel said: Am always a bit bemused by this issue. Presumably completely de-catted beasts have to have the cats stuck on again every year for MOT purposes? Does it not worry the engine's brain, e.g. lambda sensors and all that? Anything after K reg should have a cat on for Mot purposes. As regards the ecu's ikkle brain it never gets to "see" the results of a cat removal as the O2 sensor is upstream of the cat usually, so its removal isnt needed to be factored into the equation. Noticed an immediate difference on the 4 when the cat was removed even though it wasnt blocked or rattly. hth.

Luckily for me my saab is a on a J plate so the cat's not legally required removal did improve the breathing.

Boosted.

[paolow]

its worth doing, just in terms of power. when i worked at audi we had a jag workshop next door and they had an xk8 cabrio in. very nice, the guys there told me it had been decatted and bhp was up to the tune of 50 brake! i was staggered and, tbh, didnt believe him, but ive heard similar stories of huge power gains so......
also weve got a nismo 200 turbo which has been decatted and it absolutely screams into the sunset. the difference is noticable immediately.
MOT can be an issue. the key is to find a garage that will 'have a spare cat lying around that they can put on for the test' or similar.

[cptsideways]

My decatted Turbo'd MX5 has an intersting side effect when upchanging at night




Speed camera'esque exhaust flashes that light the scenery behind



Nearly every gearchange too

[hughesie2]

Just ordered a full system from Hayward & Scott, £800.00 + vat, need the car for 3 days to do a bespoke system as they have no plans, Manifold all the way back with cat replacement pipes to swap with the cats back at MOT time !

Cant wait now !

ECU map next then on the Rolling road for tweeking :suitsyousir: