Mazda 6 Forums banner

1 - 20 of 85 Posts

·
Registered
Joined
·
477 Posts
Discussion Starter #1
As I had my MS6 in the air tonight installing my clear corners, I noticed the the second cat is separate from the actual downpipe and could be easily swapped out for a test pipe. What's extra nice is the 2nd O2 sensor is before this cat, so there will be no check engine light. Hopefully one of the vendors on this site will make a simple test pipe for us.
 

·
Registered
Joined
·
101 Posts
We can have one shiped out with in a day or so. We are selling them for $150.00. If your interested give me a call. 303-341-2160

Thanks,
Tommy

 

·
Registered
Joined
·
776 Posts
This has been brought up before (I think I actually did 1st), but I do not think anyone that has done it has ever said if it helped or made it louder. I think it is only there for sound purposes. Someone chime in that has done this mod and let us know the results. :D
 

·
Registered
Joined
·
1,197 Posts
not all states have inspection...MI doesn't ;)
 

·
Registered
Joined
·
2,652 Posts
I was just noticing this last night. The crappy thing? There is a massive precat attached behind the turbo....who came up with that idea?

http://forum.mazda6tech.com/viewtopic.php?t=4210
[/b]
the pre-cat post turbo is meant for cold start emissions. it tends to warm up faster because it is placed so close to the turbo. im still wondering what they put in the CA emissions equipment. ill know once i remove the exhuast and downpipe to replace with a turbo back w/ high flow cat.
 

·
Registered
Joined
·
4,138 Posts
CP-E Downpipe and Midpipe.... hopefully soon ;)

We can have one shiped out with in a day or so. We are selling them for $150.00. If your interested give me a call. 303-341-2160

Thanks,
Tommy


[/b]
Tommy, is that the stock downpipe??? Diameter actually looks quite good...
 

·
Registered
Joined
·
2,652 Posts
you'll fail inspection with out a cat. better to get a downpipe and eliminate the precat.
[/b]
eliminating the pre cat and replacing with a downpipe might be tricky because of the placement of the O2 sensors.
 

·
Registered
Joined
·
998 Posts
eliminating the pre cat and replacing with a downpipe might be tricky because of the placement of the O2 sensors.
[/b]
Nah, just make the replacement pipe, drill the hole, weld the o2 bung. The o2 is on the pipe not the cat so that shouldn't matter. Now removing the cat and not throwing a CEL may be another issue.


That test pipe looks pretty good. Not sure if its the angle, but the straight to 45* bend looks odd on the bottom. Finish that up to the turbo so I can place an order ;-)

Jason
 

·
Registered
Joined
·
11,748 Posts
ryceboi,

I know why its there...I just think its stupid. Why couldn't they have used a dual stage cat like on the standard 6i? Would have done wonders for spoolup.

All that precat is doing right now is causing backpressure, which causes reversion, which causes a rise in exhaust temps, which increases the chance of detonation!

EPA FTW!!!
 

·
Registered
Joined
·
64 Posts
Mazdaspeed protege has the same setup. Dynos have seen 15whp jump just with a catless downpipe!
[/b]


Yeah, but how loud is it?
I think some of us here bought the car because we did not want a car that was overstated with wings and such, and was loud to.
Granted, we wouldn't complain about a bit more of an aggressive exhaust note, but if it's too loud, it's not worth it IMO.
 

·
Registered
Joined
·
2,652 Posts
ryceboi,

I know why its there...I just think its stupid. Why couldn't they have used a dual stage cat like on the standard 6i? Would have done wonders for spoolup.

All that precat is doing right now is causing backpressure, which causes reversion, which causes a rise in exhaust temps, which increases the chance of detonation!

EPA FTW!!!
[/b]
another engineering marvel by mazda. ULEV is a bitch.


Yeah, but how loud is it?
I think some of us here bought the car because we did not want a car that was overstated with wings and such, and was loud to.
Granted, we wouldn't complain about a bit more of an aggressive exhaust note, but if it's too loud, it's not worth it IMO.
[/b]
the turbo muffles a lot of sound. eliminating the pre cat isnt going to make a droning noise in your cabin.
 

·
Registered
Joined
·
5,757 Posts
I know why its there...I just think its stupid. Why couldn't they have used a dual stage cat like on the standard 6i? Would have done wonders for spoolup.
[/b]
I dunno, that 6i midpipe was extremely restrictive too.

I agree with what others have said here. While replacing the second cat with a test pipe is probably an easy, safe, CEL-free modification, it's the first cat that would be most beneficial to remove. The Subaru STI has the exact same exhaust strategy, even including the wierd O2 sensor placement. Why even put an O2 sensor before the second cat... the second one doesn't need to be monitored for efficiency because it's unnecessary?
 

·
Registered
Joined
·
4,138 Posts
So in theory a downpipe that eliminates the first cat after the turbo is going to set a CEL???

The mid-pipe looks like a nice gain though, I think i'll wait and see what is offered as a package... though on some cars a downpipe requires turbo removal which i am really hesistant on...
 

·
Registered
Joined
·
5,757 Posts
Just getting the O2 sensor out of the air stream will prevent a CEL. This can be done yourself with $5 in parts from an auto store, but most likely any aftermarket vendor will have already put an extention on.
 

·
Registered
Joined
·
998 Posts
So in theory a downpipe that eliminates the first cat after the turbo is going to set a CEL???

The mid-pipe looks like a nice gain though, I think i'll wait and see what is offered as a package... though on some cars a downpipe requires turbo removal which i am really hesistant on...
[/b]
Most vehicles only come with 1 cat. The first cat measures the o2's in the exhaust stream and tells the ecu, which then adjusts fuel trims accordingly. The second o2 comes after the cat and measures the efficiency of the cat.

With that being said, if the 2nd o2 isn't seeing what 'it should' then it will throw a cel saying "Hey, your cat is toast, replace it". Now all cars are different. Some are very strict and some don't give two craps. If the o2 is getting power and warms up and sends some signal the ecu is happy.

The ones that are strict (93+ F-bodies for example) need an 'o2 simulator' which is pretty much just a chip that sends the same constant voltage the ecu wants to see to make it think the cat is there and working.

jason
 

·
Registered
Joined
·
101 Posts
CP-E Downpipe and Midpipe.... hopefully soon ;)
Tommy, is that the stock downpipe??? Diameter actually looks quite good...
[/b]
The stock downpipe is pretty good size the only real problem is the cat.

Nah, just make the replacement pipe, drill the hole, weld the o2 bung. The o2 is on the pipe not the cat so that shouldn't matter. Now removing the cat and not throwing a CEL may be another issue.
That test pipe looks pretty good. Not sure if its the angle, but the straight to 45* bend looks odd on the bottom. Finish that up to the turbo so I can place an order ;-)

Jason
[/b]
Yeah it sucks there even needs to be bends in the test pipe but the way Mazda designed the exhaust the second flange sits at a pretty good angel. We are working on the down pipe now. We are ready to take orders on the test pipes.

Tommy
 
1 - 20 of 85 Posts
About this Discussion
84 Replies
34 Participants
Wiggum
Mazda 6 Forums
Mazda6club.com is a forum dedicated to the Mazda6 / Atenza. Come and discuss reliability, performance, modifications, and more!
Full Forum Listing
Top