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Discussion Starter #1
I very much like the idea of putting an RV6 J-pipe with HFPCs on my V6 car but not thrilled about eliminating the downstream cat in the process. Would it be silly or wildly counterproductive to install a high flow cat (perhaps a Magnaflow unit) directy at the beginning of the mid pipe? One upside I would guess is that placing a cat there would help with eliminating the rasp sound assuming I also keep some sort of resonator in the midpipe after the cat. Initial thinking would be to also use a Magnaflow catback and just splice a cat in between the flange at the J-pipe and the resonator.
 

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'15 6-6
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565 Posts
I very much like the idea of putting an RV6 J-pipe with HFPCs on my V6 car but not thrilled about eliminating the downstream cat in the process. Would it be silly or wildly counterproductive to install a high flow cat (perhaps a Magnaflow unit) directy at the beginning of the mid pipe? One upside I would guess is that placing a cat there would help with eliminating the rasp sound assuming I also keep some sort of resonator in the midpipe after the cat. Initial thinking would be to also use a Magnaflow catback and just splice a cat in between the flange at the J-pipe and the resonator.
I would keep the cat a little farther away from the J Pipe flange to avoid turbulence issues. Magnaflow "200 cell" HFCs are really 250 cell--so I'd use this if you want to maximize efficiency of catalyzing vs exhaust flow (Mil.Spec :: Universal :: 100 cell cats :: 2.5" 100 Cell Weld-In Cat).

Since everyone likes to offer their own two cents, here are mine:

1) You're already illegal in the eyes of the EPA by swapping out your stock cats for HFPCs
2) The third cat isn't doing much more exhaust scrubbing than the first two, as those light off quick from a cold start (highest emissions then). You also have 2 catalysts, one for each bank of three cylinders, and that's already likely enough to pass a sniffer test.
3) If it's an environmental/personal concern, you should do what makes you happy.
 

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Discussion Starter #3
When I first saw the cats (precats I guess) installed right at the engine like they are, I was surprised to also see that an additional cat is installed downstream. There are no O2 sensors I see downstream of the second cat so there is no way for the car's systems to even know if the second cat is or isn't doing something productive. I've never seen a system which uses two different cats in a single exhaust stream. Even my GTO just has one cat in each exhaust stream and it is putting out a lot more volume than the Honda V6.

Also, I understand your point about putting the cat farther downstream, but the farther downstream a cat gets the less useful it becomes. From a cat effectiveness standpoint, they should be as close to the engine as possible. As a side note, the JBA high flow cats I put on the GTO have never caused a CEL (there are secondary O2s downstream of the cats) and provide pretty much the same output as straight pipes (at least within 5 whp). My point being, high flow cats don't have to be much of a restriction at all.
 

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'15 6-6
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565 Posts
When I first saw the cats (precats I guess) installed right at the engine like they are, I was surprised to also see that an additional cat is installed downstream. There are no O2 sensors I see downstream of the second cat so there is no way for the car's systems to even know if the second cat is or isn't doing something productive. I've never seen a system which uses two different cats in a single exhaust stream. Even my GTO just has one cat in each exhaust stream and it is putting out a lot more volume than the Honda V6.

Also, I understand your point about putting the cat farther downstream, but the farther downstream a cat gets the less useful it becomes. From a cat effectiveness standpoint, they should be as close to the engine as possible. As a side note, the JBA high flow cats I put on the GTO have never caused a CEL (there are secondary O2s downstream of the cats) and provide pretty much the same output as straight pipes (at least within 5 whp). My point being, high flow cats don't have to be much of a restriction at all.
I understand that HFCs don't pose a flow restriction but they do affect resonance and turbulence more, especially because if you mount it to the J Pipe, it'll be right were the pipes merge together. I can't imagine it being worse than stock though.
 

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Discussion Starter #5
I can't imagine it being worse than stock though.
That was kind of my thinking. I wish I could get some first hand exposure to the difference in sound in the Magnaflow and Borla exhausts. In crappy Youtube videos the Borla sounds better but I have Magnaflow on three different vehicles and while all are different they all sound great. I know apples to oranges but my point is Magnaflow would seem to make great sounding exhaust for many different kinds of cars, can their system for the V6 Accord be bad? Too many variables I think to get a good assessment from random videos captured on a cell phone.

Anyone local to the Lincoln/Omaha area that has either Magnaflow or Borla on a V6 Accord?
 

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That was kind of my thinking. I wish I could get some first hand exposure to the difference in sound in the Magnaflow and Borla exhausts. In crappy Youtube videos the Borla sounds better but I have Magnaflow on three different vehicles and while all are different they all sound great. I know apples to oranges but my point is Magnaflow would seem to make great sounding exhaust for many different kinds of cars, can their system for the V6 Accord be bad? Too many variables I think to get a good assessment from random videos captured on a cell phone.

Anyone local to the Lincoln/Omaha area that has either Magnaflow or Borla on a V6 Accord?
Think of the PCD or HFPC and the J-Pipe as a complete header. You want that to be as free flowing as possible. You would not want to put a bottle neck at the exit of the header. Place a resonator midway on the mid pipe or closer to the mufflers. After the header the sizing of the exhaust tubing is all about keeping up velocity to pull out the exhaust.
 
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