Gutting out the stock cats - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

diss7 · 08-04-2013, 07:00 PM

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.

wparsons · 08-04-2013, 07:19 PM

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.

Apoc · 08-04-2013, 07:24 PM

Quote:

Originally Posted by diss7

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.

Opposed · 08-04-2013, 07:45 PM

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.

ML · 08-04-2013, 08:25 PM

I did this to my front pipe. Louder, and engine seems smoother. Especially at higher rpms

mrk1 · 08-04-2013, 08:58 PM

Punching out the cat and inserting a pipe the same diameter of the main pipe could probably show a small gain.

wparsons · 08-04-2013, 10:21 PM

Good luck getting a pipe through the cat on either the header or the front pipe, too many bends in there.

WolfsFang · 08-04-2013, 10:29 PM

Quote:

Originally Posted by wparsons

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.

Turbowned · 08-04-2013, 10:39 PM

Waste of time and ozone, get high flow cat and larger diameter piping.

diss7 · 08-04-2013, 10:58 PM

Seeing as this will cost nothing, I hardly see how it is a waste of time.

diss7 · 08-04-2013, 11:02 PM

Quote:

Originally Posted by Opposed

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.

bkblitzed · 08-04-2013, 11:42 PM

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..

diss7 · 08-05-2013, 12:00 AM

Quote:

Originally Posted by bkblitzed

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.

bkblitzed · 08-05-2013, 12:14 AM

Quote:

Originally Posted by diss7

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.

08-04-2013, 07:00 PM	#1
diss7 Banned Join Date: Sep 2012 Drives: AE86, 2x GT86, TE27 Location: Christchurch NZ Posts: 1,478 Thanks: 826 Thanked 1,181 Times in 522 Posts Mentioned: 33 Post(s) Tagged: 0 Thread(s)	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.

08-04-2013, 07:45 PM	#4
Opposed Senior Member Join Date: Jun 2012 Drives: 2013 Asphalt FR-S Location: Bloomington, MN Posts: 1,156 Thanks: 499 Thanked 447 Times in 294 Posts Mentioned: 7 Post(s) Tagged: 0 Thread(s)	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. __________________ Asphalt FR-S: EcuTek Visconti STG2 tune, MAPerformance turbo kit, MAPerformance 3" exhaust, Hotchkis springs, Mach-V 17x9 Awesomes. Build thread: http://www.ft86club.com/forums/showthread.php?t=30703

08-04-2013, 08:58 PM	#6
mrk1 Senior Member Join Date: Mar 2013 Drives: Sterling BRZ Ltd Location: New England Posts: 1,702 Thanks: 403 Thanked 1,389 Times in 671 Posts Mentioned: 21 Post(s) Tagged: 2 Thread(s)	Punching out the cat and inserting a pipe the same diameter of the main pipe could probably show a small gain. __________________ The Build Thread GT28RS - eBoost2 - 3.91 Final Drive - Supra LSD

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08-04-2013, 10:58 PM	#10
diss7 Banned Join Date: Sep 2012 Drives: AE86, 2x GT86, TE27 Location: Christchurch NZ Posts: 1,478 Thanks: 826 Thanked 1,181 Times in 522 Posts Mentioned: 33 Post(s) Tagged: 0 Thread(s)	Seeing as this will cost nothing, I hardly see how it is a waste of time.

08-04-2013, 11:42 PM	#12
bkblitzed is better than you Join Date: Jun 2013 Drives: 2013 raven FRS Location: Norcal Posts: 1,293 Thanks: 591 Thanked 1,347 Times in 745 Posts Mentioned: 25 Post(s) Tagged: 0 Thread(s)	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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