Cat or No Cat?

[dan mugglestone]

Have the LS2 Monaro, Currently has ASS headers onto a cat back system and K&N filter. Apart from this its as far as I know its standard ( not tuned ).
Ultimately I want to have a cam and tune up but thats for another day .

In the meantime how much benefit or lets be honest extra power would i get from running straight through pipe instead of sports cats and would this effect the running of the engine?

[SturdyHSV]

At stockish power levels I would be surprised if it made much if any difference compared to sports cats.

It does seem to give the exhaust note a harsher edge though.

It will probably smell even better

[99PBATR]

Or get yourself a switchable exhaust and go from mild burble to obscene at the touch of a button

[dan mugglestone]

99PBATR said:

Or get yourself a switchable exhaust and go from mild burble to obscene at the touch of a button

Forgot to say already have the switchable back boxs.

[99PBATR]

Ah i'm talking about switchable valves post cat with turndown pipes. They are loooud!! Im guessing the switchable back boxes are not that loud. I have 2x 100 Cell cats and no issues. I'm assuming the issue you might have if you go straight piped would be getting it through emissions. Yes you can take them off and put connecting straight pipes in. I did that for a few years with another car I had and what a bloody ball ache. Sports cats should not really hamper much performance if any.

Edited by 99PBATR on Wednesday 16th February 16:04

[Janosh]

I believe the standard cats are not restrictive unless you’re FI & chasing big power. Removing them will make your exhaust MUCH louder, not necessarily in a good way.

Once you have a decent cat back exhaust, the next step would be headers… which also don’t add much power unless you’re really pushing things.

With a stock engine and cam package, the exhaust choices are mostly about getting the right noise / volume…

If you’re chasing NA power.. then I think you should focus on the cam / heads / intake…

Sturdy - keep me hoses here, you’re better / best informed about chasing NA performance

[dan mugglestone]

Janosh said:

I believe the standard cats are not restrictive unless you’re FI & chasing big power. Removing them will make your exhaust MUCH louder, not necessarily in a good way.

Once you have a decent cat back exhaust, the next step would be headers… which also don’t add much power unless you’re really pushing things.

With a stock engine and cam package, the exhaust choices are mostly about getting the right noise / volume…

If you’re chasing NA power.. then I think you should focus on the cam / heads / intake…

Sturdy - keep me hoses here, you’re better / best informed about chasing NA performance

Thats sort of what im thinking here .
Go cat less and enjoy better noise but basically lose back pressure and a few less horses?

Sports cats give less noise but actually a better running and slightly more powerful engine.?

Is this right???????

Forced or naturally induction is for another day . Im talking natural for now.

[stevieturbo]

No.

CAT's will never improve an exhausts performance.

But in most cases, a good quality CAT will have little or no negative impact on it either. Plus you'll have an easier life at MOT time if it is all correct.

[99PBATR]

stevieturbo said:

No.

CAT's will never improve an exhausts performance.

But in most cases, a good quality CAT will have little or no negative impact on it either. Plus you'll have an easier life at MOT time if it is all correct.

Totally agree, trust me you really don't want the hassle at MOT time, i've been there, it's painful and unless you plan on taking the pipes off and refitting the CATs especially for the MOT which is a right ball ache, then stick with the sport CAT's

[fred bloggs]

Cats or not no difference on a standard engine. Same as an air filter. Nob all difference.
And forget about back pressure, it’s nonsense. The only time you want back pressure is before a turbo.

The number one mod on an ls is the cam , especially when done with proper long headers .

Has anyone done just a cam with a stock exhaust? Just wandering?

Suppose it comes down to how mad you intend to go, and how clean your mot tester wants the emissions ;-)
Saying that ,if you spent enough time and money, you could get some wild set ups to pass emissions.
Some motorbikes have crazy duration and overlaps for 12000 rpm and are euro4.

Edited by fred bloggs on Wednesday 23 February 19:07

Edited by fred bloggs on Wednesday 23 February 19:12

[fred bloggs]

Bt the way, thanks again for the subframe tool .

[dan mugglestone]

fred bloggs said:

Bt the way, thanks again for the subframe tool .

No worries glad its helping the monaro community out.


With regards to emissions and mot etc Im not to fussed as have a 2 poster and the pipes are straight like for like replacements.

If im honest I like the idea of running no cat just for the potential extra noise even if it gave me 1hp more id take it for the year until i swap it mot time.

Just wonder if i am actually confusing the ECU by having the lambda out of the flow to avoid any engine check lights making it run rich/lean?? therefore losing power?????

[Janosh]

I don’t think so, I believe the second O2 sensor is purely for measuring cat performance / emissions so you’re not losing any potential power..

[vxr2010]

On the monaro , it is noticeable to go from a broken or slow moving sensor to a better working new sensor , im sure it’s not a big impact on emissions etc but it clearly helps things to work better, in a small way