Gutting Cat Converter to place TP inside it?

[91Bomb]

I was going to remove the cat and put a test pipe in it's place but don't like the increase in exhaust noise so now I'm thinking about gutting the cat enough to get a straight pipe inside it to effectively have a TP surrounded by the remaining cat. Not doing this for appearance sake but to keep TP quieter.

Has anyone done this and how much quieter is it going to be doing it that way vs just a TP? I would be putting a 2" inner diameter TP inside the cat.

BTW could use tips for the best way + tools needed to do this job right, thanks.

 

[knochgoon24]

You really aren't going to gain much power by gutting the cat unless it's clogged.

 

[ReYnd]

Gutting the cat and putting a smaller diameter pipe inside it doesn't make any sense to me. Get a couple resonators and weld them into the catback. Pretty sure all the name-brand catbacks have them already included, so I doubt you're doing this just to avoid cutting one of them up. Another option would be to make a silencer to go in the tip of your muffler that can be taken out when you want less restriction and don't mind the extra noise.

 

[91Bomb]

I still have stock pipes on car so running a 2" ID straight pipe instead of cat will definely make a difference.


What I want to do is gut cat just enough to insert the straight pipe I have through it so it willl be not as loud because it'll be surrounded by cat material. Is the stuff inside the cat hard to knock through so I can do this?

 

[90on35psi]

The reason having the test pipe installed is louder is because the cat muffles the exhaust quite a bit. Putting a test pipe through the cat will not make your exhaust any quieter.

 

[91Bomb]

Yeah I just realized that after thinking about it awhile


So now what I'm thinking about doing is partially gutting the cat like jamming a pipe that's just smaller than the opening through there creating a flow through area and leaving some of the inside of cat intact. I'm thinking the exhaust will be louder but not nearly as bad as gutting the whole thing or running a TP.

Right now I'm running stock exhaust with bcs + hacked air can mods and need a litttle more power but don't want to boost to my planned 14 lbs without dioing SOMETHING with the cat.

What do you guys think about a partially gutting cat for this purpose? I'm figuring better flow, less heat, and exhaust noise increased just right. Don't forget I'm never going above 14 lbs either.

 

[ReYnd]

Get a high flow cat flanged up to mate with your downpipe and then have an exhaust shop make you a nice catback with a resonator or two. It really shouldn't be expensive at all. You could benefit from a 2.5" pipe, and with the high flow cat, it would be about the same if not better than running a straight 2-incher. I'm sure there are stock-looking 2.5" mufflers out there.

 

[91Bomb]

I just ordered a test pipe. Some of the test pipes on ebay say test pipe/resonator but the one I ordered didn't say that. Exactly what is inside a pipe that makes it a resonator anyway?

 

[ReYnd]

Nothing. It's just an expansion chamber. Sort of like a mini muffler, but without baffles. Basically just a length of pipe that necks up to a larger diameter and back down after a foot and a half or so. Makes the sound deeper and quieter.

You basically just bought a pipe with flanges on the ends that will replace the cat, and has the same or similar diameter to the stock exhaust. Or whatever it says in the auction description.

 

[91Bomb]

Well here's what I ordered. It should sound better than just a piece of straight pipe from auto parts store.

 

[sax_man]

I have something similar to that on my 2g gst that's still on the stock exhaust. It's really not that much louder than when the cat was in place.I think it sounds pretty good actually. Sometimes the droning gets annoying on the interstate, but I just turn up the music a bit.

 

[Zdrummer15]

The one you ordered has a resonator if it is the same as the picture.

 

[91Bomb]

Yeah That's the one I ordered. Hope I didn't screw up because even though I have a turbo 1g I ordered the N/T pipe since the inlet is 2-3/8" and lemgth is what I need. I'm attaching to stock pipes so inlet size is fine but maybe the resonator chamber is bigger or smaller for turbo cars providing a different sound. I noticed when I had my 1g N/T there was 2 resonators on it from the factory and turbo 1g's don't come with any.

 

[ReYnd]

It does have a resonator - the bulged part in the middle. If it bolts up, there's no way you can screw up. I don't recall exactly which stock pipe it is, but I'm thinking one of them is canted at some stupid angle. So depending on how the maker of your test pipe decided to do it (stock vs. standard flanging) you may have to cut a flange off and have it welded back on at the proper angle. I suggest doing it to the stock pipe so the problem is fixed once and for all. If you have a shop do it though, tell them it's for racing only though, or there may be issues.

 

[91Bomb]

I looked under the car already and the TP ordered should bolt right up

 

[LiquidX]

Well if you have visual emissions you'll need to bolt the cat back on for it. That's the reason there are faux cat test pipes. I know you ordered a test pipe already a question was asked about the insides of the cat and how hard it's to get them out.

The guts are usually a tight honeycomb of ceramic and mixed materials mixed with the ceramic. There are also metal ones available too. To gut the cat takes time to just empty it out by using a heavy rod and hammer. It's possibly to chisel out a hole but good luck doing that. The exhaust would not travel through the remaining honeycomb as it's a large restriction compared to a straight hollow pipe.

To lower noise you need larger muffler volume

 

[91Bomb]

I decided on the test pipe instead of gutting the cat. I'll be putting the cat back on for inspection.

Btw do I need to use stainless steel nuts + bolts so they don't get rust welded on there and anti-seize ?grease?

 

[LiquidX]

It's your choice if you want to use stainless hardware or not. If cost is an issue then use regular hardware and coat it all with anti-seize in case you need to pull it off.

Personally, I use anti-seize on just about everything that I can get it on to as long as it won't cause a problem with it being on it.

 

[91Bomb]

Yeah I just don't want the nuts to rust weld to the bolts because the cat needs to go back on in a year for inspection and then every 2 yrs after that. I know when I go to remove the cat to put the TP on the bolts are going to have to be sawed off and probably have to drill out the old rusted bolts.

 

[MIdsm]

You do realize that if caught with the test pipe you may be fined up to $10K and jail time, right? IMHO a couple HP just isn't worth the risk. You would be better off getting a larger diameter exhaust and cat as suggested above.

 

[Jiggalude]

You do realize that if caught with the test pipe you may be fined up to $10K and jail time, right? IMHO a couple HP just isn't worth the risk. You would be better off getting a larger diameter exhaust and cat as suggested above.

Wow, where are you from? 10,000 dollars AND jail time, for not having a cat converter on your car? Then I assume you are pretty much put to death where you live if you're caught stealing something right?

 

[ramsack]

The easiest way to gut a cat is to get a really long spade bit about 1" wide. That will chew the crap out of the cat.

 

[SuzukiRidr326]

test pipes dont really make your car that much louder if your using a stock muffler, with a aftermarket muffler youll hear a big diff but not with a stock muffler