Removing second cat in exhaust

[ozynigma]

Stratified have suggested I remove the second catalytic converter from my exhaust (CX7) as a mod before getting a tune.

Is this likely to make the car non compliant with QLD emissions standards? Does anyone care?

Could I replace it with a high flow cat near the axle/muffler?

Can anyone suggest a good exhaust specialist on the south side of Brisbane? Around Slacks Creek would be great.

Regardless of the cat, I am thinking of replacing the massive muffler behind the rear axle which has one inlet and splits to two exhaust tips with a single hi flow muffler and single tip.

[shaneski]

You can get a high flow cat welded in place of the stock one, 99.9% that mod and have a dump pipe or test pipe that deletes the the 2nd cat all together.
Where is the 2nd cat on a cx7?

[Mspec]

Woohoo popping and burbling cx7!

[ozynigma]

You can get a high flow cat welded in place of the stock one, 99.9% that mod and have a dump pipe or test pipe that deletes the the 2nd cat all together.
Where is the 2nd cat on a cx7?

The second cat is at the front just after the down pipe.



Then there is this, a resonator I think.

Untitled

And finally a massive muffler.

Untitled

The only place I have found that does off the shelf performance CX7 exhaust is CP-E.

Mazda CX7 ‘06-‘09 QKspl™ Downpipe | cp-e™

Mazda CX-7 QuickPowerâ„¢ Pipe | cp-eâ„¢

Mazda CX-7 2006-2009 Austeniteâ„¢ Dual Cat Back Exhaust | cp-eâ„¢

I was planning to keep the down pipe and first cat unmodified for stage 1 with a stock MPS K04. From my reading there is not much to be gained with a down pipe and stock turbo versus upgrading elsewhere instead.

So I am looking for minimal upgrade to the exhaust in stage 1. I am thinking a single high flow muffler with a single tip on the left to replace the massive twin pipe muffler and a straight through pipe from the down pipe to muffler.

Has anyone removed one cat and been tested for emissions?

Any suggestions for a high flow muffler that works well (and sounds nice) with our MZR engines?

Any recommendations for exhaust places on the Brisbane southside?

[SarcasticOne]

Look at the newbie FAQ in my sig... Has a link to MSF that has a heap of info on full exhaust vs 2nd cat delete/test pipe on stock turbo

[lup15]

the dump pipe was one of my first mods for the MPS3. The main thing I found after the change was that the engine is much more responsive with a lot more mid-rpm torque. mainly due to getting rid of 2 cats and replacing it with a highflow metal cat.

If you are looking for cheap power, getting rid of the 2nd cat will definately make a noticeable difference. I would hazard a guess that emissions would no longer be compliant, but as long as you have one cat I doubt anyone will care

Any straight through muffler will do the job. It comes down to construction material and the end sound. Magnaflow apparently sounds pretty good. I would keep the dual exit as the blank hole would look silly. Just run a 2nd exhaust pipe coming off a Y connection

muffler ______tip 1
           |__tip 2

Troy (@2XS) does exhaust work. I also heard good things about Mr Mufflers in Sumner Park.

[ozynigma]

the dump pipe was one of my first mods for the MPS3. The main thing I found after the change was that the engine is much more responsive with a lot more mid-rpm torque. mainly due to getting rid of 2 cats and replacing it with a highflow metal cat.

If you are looking for cheap power, getting rid of the 2nd cat will definately make a noticeable difference. I would hazard a guess that emissions would no longer be compliant, but as long as you have one cat I doubt anyone will care

Any straight through muffler will do the job. It comes down to construction material and the end sound. Magnaflow apparently sounds pretty good. I would keep the dual exit as the blank hole would look silly. Just run a 2nd exhaust pipe coming off a Y connection

muffler ______tip 1
           |__tip 2

Troy (@2XS) does exhaust work. I also heard good things about Mr Mufflers in Sumner Park.

To close this thread off. I have got some good advice from Mild or Wild Exhausts at Slacks Creek. I was impressed by what the guy knew about the CX7 (his wife worked at a Mazda dealer) and how he understood what I was looking for.

1) I can't legally delete either of the factory cats without replacing it with something. If I was doing the whole exhaust I could replace both cats with a single high flow cat.

2) We discussed putting a single free flowing muffler and tip to replace the standard muffler and twin tips.

Here is the standard muffler. You can see the bolted flange on the right hand side just behind the axle.

Untitled by ozynigma, on Flickr

I will probably do this and run a single tip like the NA and diesel CX7's (makes my modded turbo even more stealthy). Except there single exit is on the right and mine might be on the left to accommodate the muffler with minimum bends.

These are the current tips, I don't reckon it will be too obvious with one tip removed, in the long term I could replace or modify the bumper to remove the second exit.

Untitled by ozynigma, on Flickr

At the end of the day twin exhausts on a single turbo motor are always about aesthetics and not performance (flow). I would prefer to optimise the flow and ditch the redundant second tip.

[Lachlan]

If it's anything like the MPS, I wouldn't expect any more power from that catback, regardless of flow. And second cat delete might not technically be legal, but no one will notice. Mine passed an engineering cert with only one cat (there were photos of the exhaust and everything). If you don't do a DP, maybe you could just get it flanged properly so you could take add or remove the second cat in 30 mins whenever you wanted?

[ozynigma]

If it's anything like the MPS, I wouldn't expect any more power from that catback, regardless of flow. And second cat delete might not technically be legal, but no one will notice. Mine passed an engineering cert with only one cat (there were photos of the exhaust and everything). If you don't do a DP, maybe you could just get it flanged properly so you could take add or remove the second cat in 30 mins whenever you wanted?

I am sure I could find a less reputable shop to help with the cat delete and I am sure you are right about no one noticing. At this stage I am keeping exhaust mods cheap, stealthy and legal. If I need more power the next stage would be to invest a couple of grand or more in a complete 3" exhaust, manifold, dump pipe, hi flow cat etc. Thats probably more than I am spending on all of Stage 1 with upgraded K04, intake, TMIC and a tune. So at the moment my bang for buck is not in the exhaust.

[lup15]

A dump would far be better bang for buck than a cat back and can be reused for further exhaust changes if you're sticking with the K04 flange

My exhaust also sounded much more aggressive just with a dump change which may or may not be something you're after

[2XS]

The front is very similar to the 6.
How much would be very interesting.
As for the back, its like the BL system.

Any help you're after, just ask.
I'm located on Brisbane southside.

[1CMS1]

Remove the second cat, if need be put it back in for emissions testing. If the boys at stratified say to do it.....do it lol

[ozynigma]

Thanks for all the input.

I agree that DP would be best bang for buck. The issue is I don't want to spend that much at the moment and I think I can get the power I want at this stage without it. I think I would be looking at a couple of thousand at least to do the exhaust properly (and legally).

The axle back muffler replacement is only a few hundred and its more about getting a bit noisier than performance. I see it as a low cost first step in the exhaust upgrade that will be compatible with whatever I put in front of it later.

[Yeldarb]

A couple of thousand including the DP I hope.

[ozynigma]

A couple of thousand including the DP I hope.

Yes including DP and based on CPE prices. One of the only companies doing off the shelf systems for the CX7.

http://cp-e.com/webstore/?s=Cx7

Would be more if it includes the CPE cast SS exhaust manifold (and FMIC so it fits).

[2XS]

Why off the shelf?
Custom isn't always dearer.

[ozynigma]

Why off the shelf?
Custom isn't always dearer.

The OTS prices were a benchmark. I will get in touch in the next few days to see if I can afford something custom. I have a spare stock CX7 down pipe for comparison purposes.

[creole]

What are your state laws for emissions? In Vic we have to legally retain ALL emissions gear from factory, so technically its illegal in vic to have a decat test pipe. But we dont have annual emissions testing unless you are a smokey car and are unfortunate enough to get a blue epa slip for emissions testing.

You can go at your 2nd cat with mr hammer & chisel and have $0 stage 2

[Lachlan]

You can go at your 2nd cat with mr hammer & chisel and have $0 stage 2

Not a good idea. You will then be boned if you ever do get checked, plus you will add a nasty bit of turbulence. Just use a proper replacement race pipe that you can switch out for the stock one in 30 minutes if you need.