Mazda 6 Forums banner

1 - 16 of 16 Posts

·
Registered
Joined
·
490 Posts
Discussion Starter #1
Are there any high flow cats for this platform, I’m trying to see any other options besides corksport to enhance the exhaust system?
 

·
Registered
Joined
·
46 Posts
I'm planning on cutting out the stock cat and replacing with Flowmaster 200 series high flow cat (technically not legal in California, but fine anywhere else, also this is the secondary cat anyways since I'm not touching that beautiful stock exhaust header).
If you still have the big restrictive stock muffler I'm not sure it would be noticeable, but if you already have a better flowing muffler then should free up a few ponies (2-5 depending on calculations, mostly in higher RPM).
 

·
Registered
Joined
·
411 Posts
I'm planning on cutting out the stock cat and replacing with Flowmaster 200 series high flow cat (technically not legal in California, but fine anywhere else, also this is the secondary cat anyways since I'm not touching that beautiful stock exhaust header).
If you still have the big restrictive stock muffler I'm not sure it would be noticeable, but if you already have a better flowing muffler then should free up a few ponies (2-5 depending on calculations, mostly in higher RPM).
The second cat is already tiny. Replacing it with a high flow cat wont make any difference whatsoever.

A muffler upgrade is 1-2hp which will be negated by poorer aerodynamic performance. Its actually not very restrictive either, as the design is good
 

·
Registered
Joined
·
729 Posts
Nostalgic Hero put in a set of headers (which does not include the pre-cat). He retains the underfloor cat. I wonder if (and you said the underfloor cat is smallish) you could go to a high-flow underfloor cat, go to the same headers that Nostalgic Hero has... and then (obviously) NOT be emissions legal on start-up... but become emissions legal once the car is up to operating temp?

It appears that this approach will yield some decent results, say, if you combine with an axle-back decent system.

I realize this goes against what you said earlier re not wanting to muck with the stock system.... but....
 

·
Registered
Joined
·
411 Posts
Nostalgic Hero put in a set of headers (which does not include the pre-cat). He retains the underfloor cat. I wonder if (and you said the underfloor cat is smallish) you could go to a high-flow underfloor cat, go to the same headers that Nostalgic Hero has... and then (obviously) NOT be emissions legal on start-up... but become emissions legal once the car is up to operating temp?

It appears that this approach will yield some decent results, say, if you combine with an axle-back decent system.

I realize this goes against what you said earlier re not wanting to muck with the stock system.... but....
Having one high flow cat or simply keeping the second cat wouldnt be quite legal in terms of emission production, but just about.
 

·
Registered
Joined
·
411 Posts
How much power will a high-flow cat really give you? I was under the impression that modern catalytic converters aren't very restrictive in the first place.
It's mainly the design of the stock manifold which will cause restriction, and in this case the design is good. So the answer is, probably not enough to warrant being barely emissions legal.
 

·
Registered
Joined
·
490 Posts
Discussion Starter #9
I'm planning on cutting out the stock cat and replacing with Flowmaster 200 series high flow cat (technically not legal in California, but fine anywhere else, also this is the secondary cat anyways since I'm not touching that beautiful stock exhaust header).
If you still have the big restrictive stock muffler I'm not sure it would be noticeable, but if you already have a better flowing muffler then should free up a few ponies (2-5 depending on calculations, mostly in higher RPM).

Can you give me a link to this high flow cat, I'm curious to see the price and design.
 

·
Registered
Joined
·
1,158 Posts

·
Registered
Joined
·
46 Posts
The second cat is already tiny. Replacing it with a high flow cat wont make any difference whatsoever.

A muffler upgrade is 1-2hp which will be negated by poorer aerodynamic performance. Its actually not very restrictive either, as the design is good
The external size of a cat does not necessarily indicate the amount of resistance it may be creating, though my understanding is that older cats are more restrictive and would thus be a larger difference.
I've noticed you claim 1-2hp for the muffler, which seems like a significant underestimation, and it is a giant muffler so while it may not be that restrictive considering how much it quiets the sound it is still a lot of restriction/loss of exhaust gas energy.
To be fair I don't have a dyno graph to measure the exact difference, but my muffler upgrade was a VERY noticeable difference on my butt-dyno with the car pulling faster and just feeling like there was less lag between pushing the pedal and the car moving. If it were only 1-2hp I don't think it would be that noticeable. Also in my case I think it is hardly any aerodynamic reduction and about 40lbs lighter.

I think I've mentioned this before, but anytime we're talking about intake or exhaust then you have to consider the cumulative changes. It is often the case that on a stock car with nothing else changed just doing an Axle-back exhaust upgrade will hardly net any performance benefit, but if that same car has other mods that are allowing it to flow more air (e.g. Tune, intake) then the benefit of the changes to the exhaust will be amplified. Same is true for the cat, where the benefit may be unnoticeable in otherwise stock form, but noticeable if the exhaust is already flowing better and that cat is now a key restriction point.

In the end it is entirely conceivable that a high flow cat change might not be noticeable (though I doubt that, with my setup at least), but <$100 for the possibility of a few more ponies seems like a worthwhile try (I am not going to do anything crazy like turbo this car so looking to squeeze all I can out of it within reason).
 

·
Registered
Joined
·
46 Posts
Can you give me a link to this high flow cat, I'm curious to see the price and design.
I don't have it off hand at the moment, but just look on Amazon for 2.5" 200 series cat (that is important, the 200 series is the metal substrate with less cell density, which means less restriction or flow interference). I think it's like $60, I'm going to unbolt the mid-pipe myself then take it to a local shop to cut out the old and weld in the new for like $10.
(Technically it's a Christmas present from one of my kids :), but I'll try to snap some pics comparing stock to the new one when I get it done).
 

·
Registered
Joined
·
411 Posts
The external size of a cat does not necessarily indicate the amount of resistance it may be creating, though my understanding is that older cats are more restrictive and would thus be a larger difference.
I've noticed you claim 1-2hp for the muffler, which seems like a significant underestimation, and it is a giant muffler so while it may not be that restrictive considering how much it quiets the sound it is still a lot of restriction/loss of exhaust gas energy.
To be fair I don't have a dyno graph to measure the exact difference, but my muffler upgrade was a VERY noticeable difference on my butt-dyno with the car pulling faster and just feeling like there was less lag between pushing the pedal and the car moving. If it were only 1-2hp I don't think it would be that noticeable. Also in my case I think it is hardly any aerodynamic reduction and about 40lbs lighter.

I think I've mentioned this before, but anytime we're talking about intake or exhaust then you have to consider the cumulative changes. It is often the case that on a stock car with nothing else changed just doing an Axle-back exhaust upgrade will hardly net any performance benefit, but if that same car has other mods that are allowing it to flow more air (e.g. Tune, intake) then the benefit of the changes to the exhaust will be amplified. Same is true for the cat, where the benefit may be unnoticeable in otherwise stock form, but noticeable if the exhaust is already flowing better and that cat is now a key restriction point.

In the end it is entirely conceivable that a high flow cat change might not be noticeable (though I doubt that, with my setup at least), but <$100 for the possibility of a few more ponies seems like a worthwhile try (I am not going to do anything crazy like turbo this car so looking to squeeze all I can out of it within reason).
The muffler on this car is only big for aerodynamics purposes- if you cut it open, the piping inside only makes up a small portion of the internal cavity. It's a Hemmholtz resonator design which is actually quite excellent at managing exhaust back pressure with overall flow. I say 1-2 hp because no matter what sort of muffler design you're dealing with , no matter how restrictive, its the most gains you can physically gain from such an upgrade. I changed the VERY restrictive muffler on my BMW out for a magnaflow back in the day and while there was a difference, I swear it was no more than 2hp and only winding out past 4500rpm. It's more of a sound mod than anything else.

Mazdas stock exhaust is a great design and I wouldn't say it's very quiet at all in stock form, hence the potential to squeeze any power out of it, especially being an NA motor is very limited. Youd get a better result swapping out the huge factory resonator for something high flow.

As for the second cat, it is a very small cat both in terms of size and the number of cells it has. Its just for warmup emissions meaning it's not supposed to be big. Plus I believe its monitored meaning it's a bad idea to mess with it. Honestly, replacing it would probably make zero difference whatsoever.
 

·
Registered
Joined
·
1,158 Posts
The external size of a cat does not necessarily indicate the amount of resistance it may be creating, though my understanding is that older cats are more restrictive and would thus be a larger difference.
I've noticed you claim 1-2hp for the muffler, which seems like a significant underestimation, and it is a giant muffler so while it may not be that restrictive considering how much it quiets the sound it is still a lot of restriction/loss of exhaust gas energy.
To be fair I don't have a dyno graph to measure the exact difference, but my muffler upgrade was a VERY noticeable difference on my butt-dyno with the car pulling faster and just feeling like there was less lag between pushing the pedal and the car moving. If it were only 1-2hp I don't think it would be that noticeable. Also in my case I think it is hardly any aerodynamic reduction and about 40lbs lighter.

I think I've mentioned this before, but anytime we're talking about intake or exhaust then you have to consider the cumulative changes. It is often the case that on a stock car with nothing else changed just doing an Axle-back exhaust upgrade will hardly net any performance benefit, but if that same car has other mods that are allowing it to flow more air (e.g. Tune, intake) then the benefit of the changes to the exhaust will be amplified. Same is true for the cat, where the benefit may be unnoticeable in otherwise stock form, but noticeable if the exhaust is already flowing better and that cat is now a key restriction point.

In the end it is entirely conceivable that a high flow cat change might not be noticeable (though I doubt that, with my setup at least), but <$100 for the possibility of a few more ponies seems like a worthwhile try (I am not going to do anything crazy like turbo this car so looking to squeeze all I can out of it within reason).
On a turbo car, a cat elim pipe can be worth 30hp depending on the rest of the mods done.
 

·
Registered
Joined
·
46 Posts
The muffler on this car is only big for aerodynamics purposes- if you cut it open, the piping inside only makes up a small portion of the internal cavity. It's a Hemmholtz resonator design which is actually quite excellent at managing exhaust back pressure with overall flow. I say 1-2 hp because no matter what sort of muffler design you're dealing with , no matter how restrictive, its the most gains you can physically gain from such an upgrade. I changed the VERY restrictive muffler on my BMW out for a magnaflow back in the day and while there was a difference, I swear it was no more than 2hp and only winding out past 4500rpm. It's more of a sound mod than anything else.

Mazdas stock exhaust is a great design and I wouldn't say it's very quiet at all in stock form, hence the potential to squeeze any power out of it, especially being an NA motor is very limited. Youd get a better result swapping out the huge factory resonator for something high flow.

As for the second cat, it is a very small cat both in terms of size and the number of cells it has. Its just for warmup emissions meaning it's not supposed to be big. Plus I believe its monitored meaning it's a bad idea to mess with it. Honestly, replacing it would probably make zero difference whatsoever.
To each their own I guess, in the end I am most happy with the sound (went with classic turbo muffler) and was pleasantly surprised that it felt a little snappier on the throttle.
Interesting that you mention the resonator, it had never occurred to me, I thought a resonator wouldn't impede flow at all?
 

·
Registered
Joined
·
490 Posts
Discussion Starter #16
I don't have it off hand at the moment, but just look on Amazon for 2.5" 200 series cat (that is important, the 200 series is the metal substrate with less cell density, which means less restriction or flow interference). I think it's like $60, I'm going to unbolt the mid-pipe myself then take it to a local shop to cut out the old and weld in the new for like $10.
(Technically it's a Christmas present from one of my kids :), but I'll try to snap some pics comparing stock to the new one when I get it done).
Perfect, I think I may also do this. Let us know how it goes :)
 
1 - 16 of 16 Posts
Top