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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 08-04-2013, 06:00 PM   #1
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Gutting out the stock cats

Has anyone gutted out the stock cats?

We used to do this back in the day, and it was always a cheap gain. Admitidly on 10 year old cars with clogged cats.

But, would be interested if someone has tried this. Might get 50% of the gains of a $2000 exhaust system for 1 hours work on a hoist.

I like the idea of it, from a stealth/sleeper point of view.
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Old 08-04-2013, 06:19 PM   #2
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You'll get better gains from larger diameter piping than from just gutting the cats in the stock header/front pipe. I would bet you get less than 1-2hp from gutting the stock cats but without replacing anything else.
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Old 08-04-2013, 06:24 PM   #3
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Originally Posted by diss7 View Post
Has anyone gutted out the stock cats?

We used to do this back in the day, and it was always a cheap gain. Admitidly on 10 year old cars with clogged cats.

But, would be interested if someone has tried this. Might get 50% of the gains of a $2000 exhaust system for 1 hours work on a hoist.

I like the idea of it, from a stealth/sleeper point of view.
Great idea. You should do it and tell us how that works out.
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Old 08-04-2013, 06:45 PM   #4
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You will most likely lose or not gain any power. Your better off with a straight through same diameter pipe. The hollow cat will disrupt the exhaust flow and scavaging effect.
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Old 08-04-2013, 07:25 PM   #5
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I did this to my front pipe. Louder, and engine seems smoother. Especially at higher rpms
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Old 08-04-2013, 07:58 PM   #6
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Punching out the cat and inserting a pipe the same diameter of the main pipe could probably show a small gain.
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Old 08-04-2013, 09:21 PM   #7
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Good luck getting a pipe through the cat on either the header or the front pipe, too many bends in there.
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Old 08-04-2013, 09:29 PM   #8
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You'll get better gains from larger diameter piping than from just gutting the cats in the stock header/front pipe. I would bet you get less than 1-2hp from gutting the stock cats but without replacing anything else.
you wont see any gains gains going any bigger then 2.5 if you stay NA.
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Old 08-04-2013, 09:39 PM   #9
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Waste of time and ozone, get high flow cat and larger diameter piping.
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Old 08-04-2013, 09:58 PM   #10
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Seeing as this will cost nothing, I hardly see how it is a waste of time.
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Old 08-04-2013, 10:02 PM   #11
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You will most likely lose or not gain any power. Your better off with a straight through same diameter pipe. The hollow cat will disrupt the exhaust flow and scavaging effect.
Understand. But, going for sleeper install. Replacing cat with shiny new decat pipe, is a give away. Gutted out stock cat will still look stock.
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Old 08-04-2013, 10:42 PM   #12
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how many cats do our cars have? 1 header, 1 over pipe, and is there one in the downpipe as well? Ugh i miss only having 1-2 cats being only in the downpipe..
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Old 08-04-2013, 11:00 PM   #13
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how many cats do our cars have? 1 header, 1 over pipe, and is there one in the downpipe as well? Ugh i miss only having 1-2 cats being only in the downpipe..
There is one in the header, one in the front pipe. Removing the one in the header causes issues, as there are sensors before and after the cat, that will then think there is an issue and throw a CEL.

There are ways & means around this CEL, but there is mixed reviews on the success of these methods. Of cuorse you could get a flash/tune to solve this.

The one in the front pipe is not measured in this way, and can be removed without issue.

I'm all about keeping my 5 year warranty. Also, we have to get our cars inspected yearly, and they love failing modified cars.
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Old 08-04-2013, 11:14 PM   #14
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There is one in the header, one in the front pipe. Removing the one in the header causes issues, as there are sensors before and after the cat, that will then think there is an issue and throw a CEL.

There are ways & means around this CEL, but there is mixed reviews on the success of these methods. Of cuorse you could get a flash/tune to solve this.

The one in the front pipe is not measured in this way, and can be removed without issue.

I'm all about keeping my 5 year warranty. Also, we have to get our cars inspected yearly, and they love failing modified cars.
ah okay thanks. I might just gut the overpipe cat then.
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