3.0r 3rd cat delete legality and emissions?

Posts specific to the 3.0 litre NA H6 engine

3.0r 3rd cat delete legality and emissions?

Postby edenotto9 » Wed Jul 12, 2017 12:08 am

Hey everyone.
From searching around the forums i have discovered that it's a common mod for 3.0s to delete the 3rd cat. However after reading the legislation im beginning to have second thoughts on how legal this is, so i thought i would make a post to get some second thoughts.

Also putting legality aside, does anyone know if removing the 3rd cat would cause the car to fail an emissions test? From what i have heard its a rather worthless addition to the system, but then why did subaru include it in the firstplace if it doesnt impact the emissions?

(forgive me if i made any mistakes in posting this, first time posting)
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Re: 3.0r 3rd cat delete legality and emissions?

Postby Swipez » Sun Jul 16, 2017 1:41 pm

To be honest with you, without the "oh if you do this, and this" BS, by deleting the 3rd cat, you will definitely change the emissions, therefore being rendered 'illegal'. There is nothing you can do about that other than paying big money for a professional to sort you out a full exhaust system that can bring you greater performance while maintaining the same emission values. But that just isn't viable for 99% of us.

So let me say this, by deleting the 3rd cat (and if you are running aftermarket headers) you will more than likely get a new rasp tone above 3k rpm that sounds dreadful. If you really want to delete the 3rd cat, I'd recommend doing other supporting exhaust mods while you're at it, including a nice high quality resonator to cut out the unwanted frequencies. I have spent a LOT of time and money on different exhaust set ups on my 3.0L. I have now concluded that having raptor headers>2x hi flow cats>vibrant performance resonator>oval straight through muffler>twin rear mufflers gives me all the added tunable performance and is under the sound limit for nsw road cars of 90db, but still sounds fantastic.

If I were to get emission checked, I'm sure my car would fail as it is flowing far too much compared to stock, and with 200 cell cats. However, the likelihood of me getting referred to a full test like that from a police officer is near non existent, due to how quiet my car is, and I have all necessary parts like cats, mufflers and resonators. So on the side of the road, a police officer wouldn't t be able to defect me unless he had x-ray vision and the ability to recognise cell counts on the fly, which just will never be the case.

Just don't be a wanker on the road and you'll be trouble free 100%.

Hope I've helped,
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Re: 3.0r 3rd cat delete legality and emissions?

Postby tom_kauf » Tue Jul 18, 2017 11:21 am

I agree with Swipez, it is technically illegal. But I didn't know any state in Australia had emissions testing. I hadn't even heard of police being able to make you get one, but I'm only familiar with QLD rules. So it sounds like some states do have that.

To give you some idea of how good a new aftermarket 200cell Cat can be: The factory down pipe on my GTSpecB had 2 cats (at probably 700cell or more each). My aftermarket downpipe has 1x 200cell Cat. The ECU was tuned for it, but no 'Catalytic Converter Efficient' codes disabled. It didn't throw a 'Check Engine Light' for about 4 years. The first one came on last week. I cleared it and it hasn't come back since.

I don't know exactly how that compares to values at an Emissions Test Centre, but the ECU was happy with the Cat's performance for all those years.
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