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-   -   how to make oem cat into a high flow one (https://www.rx8club.com/series-i-tech-garage-22/how-make-oem-cat-into-high-flow-one-109362/)

StealthTL 09-01-2007 04:00 PM

It will all come out clean, the ceramic is held in place by fibre around the edge, once it's broken up, the fibre falls out too.

Silverguy is right, don't start this unless you have a couple of days free......

As projects go, this rates up there as

".....fuck - this IS impossible!"

or

"Jeebers, I wish I'd never STARTED this shit!"

You should also have the right size (metric) thread-tap on hand to clean up the sensor hole, because you WILL smash the threads.

S

DOMINION 09-01-2007 04:07 PM

^Yup and thats why I was picking this apart. I want to know ex what the hell I'm doing befor I start. This way I know how long it will take me to do the job. This will have to wait till another time.
I thank you all for the great info and being patient with me. Now I just need some advil.

dothackRAVE 09-02-2007 12:28 AM


Originally Posted by mac11 (Post 2036300)
what the hell do you mean the longer you drive this thing the more power you will get? where did that come from?

It was a conclusion I drew from a few observations I made from your posts (your, as in forum users). I'm just wondering WHY you'd want to do this. Does it make the car go faster? Does it make it sound better?

If it makes it go faster, that means that the more catalyst you use (ie, the more you drive), the faster it goes. Sounds ridiculous to me.

Which brings me to another gain: audio. If you want better audio, get a MazdaSpeed exhaust.


And I am going to assume this is your first rotary vehicle? They run quite a bit louder than piston motors naturally so you can really tell Mazda used a very baffled muffler and cat from the factory to get the car as quiet as it is. With as much as the cat itself quiets down the car there is a good amount of restriction in that piece. You will see the biggest improvement in power by replacing the cat as compared to a cat back exhaust, header, intake, u/d pullies, etc.
Yes, its my first rotary. However, this concept of a "quiet" RX8 is completely alien to me, since I have a MazdaSpeed exhaust, and you can hear Rena coming before you ever see her. Not to mention that the purr of the rotary + MazdaSpeed exhaust is just so freakin orgasmic I see music in the stereo as an obstacle (hence I turn them off and just listen to the symphony that my right foot tells the engine to play. IT'S BEAUTIFUL!).

CnnmnSchnpps 09-02-2007 12:55 AM


Originally Posted by dothackRAVE (Post 2038444)
If it makes it go faster, that means that the more catalyst you use (ie, the more you drive), the faster it goes. Sounds ridiculous to me.

It sounds ridiculous cos it ain't so... During normal operation catalyst gets "burned through" (the chemicals are used up) but the solid stuff still stays to impede the exhaust flow. The point of this to remove this extra "stuff" that some people believe serves no purpose (I am still not convinced).

As for power gains, it will not be anything dramatic, but if any exhaust mod will yield power this one certainly will. Not sure how this would stack up against a high-flow cat, though...

Silver_Surfer 09-02-2007 03:12 AM

Well I'm done:puke: All StealthTL stated above is TRUE! I was thinking what the fuck have I started! Could've been cruzing around or watching a movie. Cars all put together but its to late and I'm too dirty & tired to start or drive my car. Will report back tomorrow.

Estimated time to complete 29hrs with long breaks in between. My breaks were needed because two times I almost just wanted to punch-out the the whole cat material out from the front end which would have made this job a 1-2hr job.

***If you have the extra cash laying around dont do this mod, just buy a supercat or something. But if your short on cash or saving for something else(Like me:) ) maybe this mod maybe for you.****

Spinning Sushi 09-02-2007 05:52 AM

I have really been thinking of doing this mod.... unfortunately, I lack the time AND patience to do this so... anybody wants to do it for me? :rolleyes:

Maybe at SSX.... just maybe...

DOMINION 09-02-2007 06:43 AM

Silver_Surfer, See thats why I was all questions on picking this apart for the ones like you and me that dont have 3-4, or more days time to complete this mod.
I was going to do it but after going over what has to be done; Time vs money, well money wins. I'll just buy a full exhaust system.

Spin9k 09-02-2007 07:49 AM


Originally Posted by Silver_Surfer
Well My breaks were needed because two times I almost just wanted to punch-out the the whole cat material out from the front end which would have made this job a 1-2hr job.

That's a good point, anyone done just that and turned it into a CATless midpipe w/giant resonator? It certainly looks like the OEM resonator may be more effective than the small diameter things on some midpipes. Wonder if it's enough to quiet it down (to 90db) when using a CAT back exhaust?

Silver_Surfer 09-03-2007 03:22 AM

Results: No cell:) Revs alittle faster, butt dyno feels alittle better. I would say from the way people describe the gains are about the same as a AP underdrive pulley but with alittle more deeper sound(I like!) I 'm not going to dyno it but I would guess its about the same or on par as a A/M supercat.

If anyone is going to do this mod buy a 4ft section of springsteel rod(I used my expensive nylon coated dewey rifle cleanning rod:Eyecrazy: ) After stroking the rod back & fourth(Having sex with my cat with no climax:banghead: ) for awhile I came up with an idea. I bent the front 1.5in section to about 75-80 degrees, pushed the rod into the back of the cat, hooked the other end to my drill and "Roto-Rotered it. Made quicker work.

Silver_Surfer 09-03-2007 03:38 AM


Originally Posted by DOMINION (Post 2038634)
Silver_Surfer, See thats why I was all questions on picking this apart for the ones like you and me that dont have 3-4, or more days time to complete this mod.
I was going to do it but after going over what has to be done; Time vs money, well money wins. I'll just buy a full exhaust system.

Yeah, I hear you!
I striped one of the front exhaust studs taking the cat off. Was a bitch to change. I did save a bunch(Geico) of cash but would I do it again? I just dont know.

zenmoused 09-03-2007 01:14 PM

Well considering a supercat is about $400 new, it may be worth the trouble for someone who cannot devote unlimited funds to their car. For me it comes down to the fact that I have about $500 to spend on my next mod, and this way I can have a high-flow cat AND a nice cat-back.

PS- didn't get to it this weekend. Silver- did you take any pics?

Silver_Surfer 09-03-2007 03:01 PM


Originally Posted by zenmoused (Post 2039246)
Well considering a supercat is about $400 new, it may be worth the trouble for someone who cannot devote unlimited funds to their car. For me it comes down to the fact that I have about $500 to spend on my next mod, and this way I can have a high-flow cat AND a nice cat-back.

PS- didn't get to it this weekend. Silver- did you take any pics?

Sorry no pics. But pics really wont show anything except rods sticking out of the cat. One tool I used that really helped was a 3-4 ft stainless rod. I had it shaped into a straighten Z with one end sharpened to stab and pry at the cat material through the 02 hole. The other end(shorter was my handle. The pointed end of the rod had to keep being reshaped as working deeper into the cat untill reaching all the way through. At first I was only working from the 02 sensor hole but the shit had nowhere to go so I had to figure a way to make a hole all the way through so the stuff would fall through. Thats where the springsteel rod came in use.

zenmoused 09-04-2007 12:36 PM

Thanks man- I'll give it a go when I put my new catback on.

Silver_Surfer 09-24-2007 01:07 AM

[QUOTE=Silver_Surfer;2038810]Results: No cell:) Revs alittle faster, butt dyno feels alittle better. I would say from the way people describe the gains are about the same as a AP underdrive pulley but with alittle more deeper sound(I like!) I 'm not going to dyno it but I would guess its about the same or on par as a A/M supercat.


***Update*** I just got finished installing my AP underdrive pulley. I had more gains with the cat mod than the AP underdrive pulley. Heck, felt little to no gains on the butt dyno. Wish someone could do a dyno test on both cats.

dozer 10-01-2007 11:44 AM

alright to be honest i have no idea what you guys are talking about????first of all can someone tell me where i can get info on how an exhaust works....and how it differs from a straight pipe, and how it differs from a hi-flow,and what exactly a midpipe does and what exactly is a muffler then???im still in the process of understanding fast cars, i wasnt really interested in how a car goes fast untill my friend got an evo8, then i startd to ask myself how does this work, so i have very little knowledge on how the exhaust systems work....can some fellow 8 drivers give me some helpful info, hints, and advice....

Silver_Surfer 10-01-2007 12:01 PM


Originally Posted by dozer (Post 2078689)
alright to be honest i have no idea what you guys are talking about????first of all can someone tell me where i can get info on how an exhaust works....and how it differs from a straight pipe, and how it differs from a hi-flow,and what exactly a midpipe does and what exactly is a muffler then???im still in the process of understanding fast cars, i was really interested in how a car goes fast untill my friend got an evo8, then i startd to ask myself how does this work, so i have very little knowledge on how the exhaust systems work....can some fellow 8 drivers give me some helpful info, hints, and advice....

Go slow and research! Dont do any mods/changes that cannot be reversed and you'll be OK.


And DONT DO THIS MOD!!!!!!!!!!!!!:)

Kal-el 10-01-2007 06:51 PM

so, exactly how much more power/better mileage am I gonna see if I fornicate the cat converter with an Iron rod, sorry if this is old but I'm a noob

Silver_Surfer 10-02-2007 01:59 PM


Originally Posted by Kal-el (Post 2079423)
so, exactly how much more power/better mileage am I gonna see if I fornicate the cat converter with an Iron rod, sorry if this is old but I'm a noob

To be honest. Very little!

olddragger 10-07-2007 08:08 PM

it will come in handy also if you supercharge! it also helps the cat run cooler if you track your car.
olddragger

CnnmnSchnpps 10-08-2007 01:44 AM


Originally Posted by olddragger (Post 2084496)
it will come in handy also if you supercharge! it also helps the cat run cooler if you track your car.
olddragger

True on the supercharger, but if you have that big a budget you might as well buy a high-flow unit and spare yourself the headache... or just get a midpipe...

If you do alot of tracking, a midpipe would be a good investment also, even if you only put it on for track days.

Not saying don't do it, just think of the options :)

olddragger 10-08-2007 05:37 PM

already did it and i have a midpipe for the track----we think alike
OD

needmorespeed 10-10-2007 12:12 AM

Mines goin bye-bye this weekend, hope I don't catch any flak at the shop here on post...


I kinda miss the muscle car...it was so much more straight-forward


Thanks for all the info guys

Phish806 11-01-2007 02:21 PM

i plan on doin this tonight when i get off of work ... i hope to do it about four or five hours with the cut in two and weld back together method... any suggestions before i dive in ?

StealthTL 11-01-2007 02:31 PM

Using the chop-n-gouge method loses one of the advantages of this method - undetectability. The weld will be fairly obvious, unless you can get the heat shield off/replaced in good shape.

mac11 11-01-2007 02:34 PM

unless he cuts and rewelds on the original seam.


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