Rotorain

Hello everyone, I was reading up about gutting the cat vs. buying a high flow cat and resonator, and figured I'd try gutting my cat before I go spending $200-500 on a cat/resonator.

I was bored at work today so I threw it up on a lift and took a look at how hard it would be to get it off. Turns out it's really easy, so I decided to pull the trigger and gut it. Took 15 mins to get the pipe off because one of the rear bolts (with the spring) really didn't want to come off. Had to use a handle off a floor jack to bust it loose. From there it was smooth sailing (plus a burn on my wrist) to get it off and get the o2 sensor off.

I set the pipe in a plastic 55 gallon drum (we use them as garbage cans) with the cat facing up. I couldn't see any light through it even when shining a bright led shop light up the back end, so it may have been partially plugged. I'm not sure how to test how plugged they are, but I'm not worried anymore haha. I took a big pry bar and a hammer, and started smashing the cat material up and dumping it out the top every once in a while. Once I got through the second layer, most of it fell out the bottom. It took me about 10 mins to bash it all out and scrape the residual stuff off the sides, but it's hard work on a hot day.

Getting the front of the cat to clear the flange on the end of the exhaust manifold was interesting, but once we got it slipped together it was smooth sailing putting it all together. 20 mins to put it back together, put the sensor back in, and clean up my tools.

Startup went totally fine, and I immediately noticed that it had a deeper exhaust note, with a much more 'full' tone. I like it. Revving it spewed a whole bunch of cat dust, but it sounded much nicer, and had a little bit of popping and crackling when I let off the throttle. I didn't get a CEL, but I have a Cobb AP so I am pretty sure the AP handled the change for me.
Here's a video of the first start:
I took it to another parking lot after work with my coworker and opened up the throttle a lot more. It doesn't sound much different at high rpms, maybe slightly louder but not much. It pops and crackles when I let off the throttle, but not so much when I am driving. The best part though is that if I rev it up to 7k+ rpm, let off, then punch the throttle again it blows nice 8" fireballs out both exhaust pipes. I bet it will do this when I get it good and hot, and shift at high rpms.
Here's a video in the parking lot:
Driving it, the exhaust note is deeper and slightly louder at low rpms, winding up to the usual rotary scream at high rpms. It seems like it flows better, with less sluggish acceleration, a bit faster throttle response, and maybe a slight power boost, it's hard to tell.

I'll update as I learn more about all the effects that this has on the car, but I test drove it a bunch today and i'm pretty excited about such good results from 0$ and only an hour of labor.

Rotorain

Update:

The tone is slightly deeper, mostly when decelerating. I don't know if it shoots fire because I can't see my exhaust, but it makes a pop on some high rpm quick shifts, which on other rotaries seems to come with a fireball. It smells like unburned fiuel, but I like it so I don't mind. You can't smell it in the car once it is warmed up, and it is very faint until then. The car also seems faster, my AP says I gained 2 hp. I don't know exactly how much my car weighs so the absolute HP isn't accurate, but I used the AP to find horsepower before and after and this change in HP should be accurate. Feels like more than 2 hp, and the sound is increased, but not a whole lot so I can still drive it around my neighborhoods at night.

New Yorker

Wish we could do that here. Illegal in NY. Supposedly "makes the air dirtier," i.e. smog, particulates, respiratory problems, asthma with little kids, etc. Have you ever heard of such BS?!

BigCajun

iTrader: (1)

Um, I don't think it's BS, It's pretty much fact that cats clean up emissions.
It's more or less a personal choice on spending the money trying to keep one knowing how easy it is for 8s to kill them.

I'm catless, so I obviously don't care. Filthy, putrid, slob club.

Emery_

iTrader: (8)

Nice, a gutless is one of the more quiet options one can get rather than getting a mid pipe, unless you get a BHR. My single exit is too loud for a regular mid pipe, but my gutted cat keeps it bearable and it's cheaper...

Btw you're CEL light will come on soon... The cobb doesn't automatically cancel out the code, you have to modify your tune in order to hide a particular code.

Junkman 6394226

I got about 140hp boost from gutting my cat/going straight pipe. But then again, my cat was completely clogged. Now i just keep the fancy straight pipe and use the gutted cat for inspections

Rotorain

The catalytic converter does greatly reduce harmful emissions by 'catalyzing' harmful particles and gases into less harmful configurations of those elements. As far as causing asthma, I don't know, but it definitely does clean up the emissions. On the other hand, it was restricting about three precious horsepower, so it had to go. Unless you boost these cars, it is really hard to make more power, so I'ma take every one I can get. It is also illegal in my state, but they only check it at the emissions place every 2 years, and the re-tune from the AP gets rid of the CEL so I will pass fine.

I was considering getting a high-flow cat and resonator, but I didn't want the extra noise, and my sohn omp adapter injecting 2-stroke oil apparently burns through cats pretty quick, so I figured that I would go the free route and bash out the inside of mine.

patrick_andraste

Didn't you just break out the last half of it? so there is still some of the catalyst inside, just not all of it.

9krpmrx8

iTrader: (46)

Gutting your cat is like cutting the springs to lower your car.

alnielsen

iTrader: (4)

Rotorain

I didn't save any of the cat, it's now just an empty cavity in my exhaust.

And yes, I realize this is a sub-optimal way of eliminating the inefficiency of a stock cat, but this was free, easy, and didn't make my car very much louder. Someday I probably will get a legit high flow cat/resonator/midpipe, but going cheap here allowed me to order my headers.

Chibana

I remember reading somewhere for one of my previous cars that gutting the cat actually reduced power due to turbulence in the cat chamber or something along those lines. Don't know about the RX-8, but I know I won't be going that route.

9krpmrx8

iTrader: (46)

It's header and a proper midpipe and exhaust system is far more beneficial than 99.9% of the aftermarket exhaust manifolds available for the RX-8.

davidsrx8

so ur saying its better to leave the cat ungutted?

BigCajun

iTrader: (1)

If you have a healthy, unclogged, not broken up cat, yes, leave it ungutted.

If your cat is clogged, or breaking up, and you cannot afford a new cat or midpipe, you most likely will damage your engine if you continue to drive it without gutting it.

Chibana

Definitely! I didn't mean to imply you should run your car with a clogged cat. I'm just saying that I'd get a cat-less midpipe before I gutted my cat, but my RX-8 isn't my daily driver, so it can sit in the garage as long as it would take me to get the money and opportunity to install the midpipe.

Rotorain

My friend got a cat less midpipe, and it increased the volume of his car by about 50%, which I really don't want. The racing beat high flow cat and resonator seems like the best way to go, but I don't have the money for it right now. The whole point of this post is that I took the cheap option and it is working great. To anyone considering it, I definitely think it is an upgrade from stock even if your cat isn't plugged.
I just got a header, which changed up my exhaust system more than gutting the cat, but I'll write a different post about that.

BigCajun

iTrader: (1)

Hello,
If I understand you, you are advocating gutting your cat even if it's good?
If so, IMHO if someone wants to delete their cat, I would suggest a better alternative would be to sell it or swap it for a BHR resonated midpipe. It's not much louder than stock.

Rotorain

The BHR resonated midpipe is great, I agree. But it costs money, and someone's cat is going to plug when they don't have money to buy one, so i'm confirming that gutting it works fine and will pass for legal in a lot of places. Until you need that extra 2 hp that the BHR gives you over a gutted cat, this option seems to work better than a (breaking) stock cat, and is totally free. I always recommend an actual replacement part and will be ordering one at some point, but right now I don't see the problem with this option.

cretinx

Correct.

Cheap (free), and if done correctly, works very well.

9krpmrx8

iTrader: (46)

Gutting your cat and cutting springs never works very well. Do it right or don't bother doing it at all.

alnielsen

iTrader: (4)

cretinx

Really?
How many wheel to wheel races have you run?
Where is your engineering degree from?

The last race car that I competed in had cut springs and they worked just fine.

Perhaps cutting 3 coils and leaving stock shocks might not be the smartest, but you can cut springs conservatively to both increase spring rate AND lower ride height.

Same with the gutted cat - is it ideal? Probably not. Is it better than stock? Absolutely.

Is the cost/benefit analysis there?
Improved performance, 0 cost.
Turbulence through the cat is the least of your worries, particularly with these cars, and particularly given how restrictive to airflow a cat truly is.

Would I ever run a car without a cat on public roads?
No.
I don't like to commit federal crimes which include potential jail time and 4 figure fines.

paimon.soror

iTrader: (15)

here we go...

alnielsen

iTrader: (4)

I approved of his message. I road raced SCCA for 10 yrs with RX7's. Autocrossed various different cars (in stock and modified classes) before that. You don't need to have an engineering degree (I'm closer to an EE than an ME) to know what works and what doesn't. It's called experience. If you want to eliminate a cat, the best way to do that is a midpipe replacement. It isn't expensive at about $300, so that really isn't an excuse.

Modifying your emissions is a federal crime. This would include blowing out the cat.

As for me, my car is not a race car. I have emissions testing here. I run stock.