Hey guys, at first i just wanted to hollow out my cats, but a friend of mine suggested that i shound just replace and cats with a straight pipe to the muffler, i'm running all stock. Any ideas, also how hard would it be for me to fabricate my own cat removal exaust pipes. if anyone has had any experience, or ideas, or even regarding the benifits of cat removal compaired to cat hollowing, it would be great.

thanks in advance guys.

-Matt

 

While everyone is pondering this guy's situation, I suppose I will use this thread to ask my exhaust question as well.

I know my cat is toast, and from what everyone says, I can expect an obvious power increase when it is replaced.

Now, would I get more power, if it were just STRAIGHT pipes to whichever muffler I choose? Or, is there a power benefit to having some restriction in the cat?

 

Just get this thing : http://racingbeat.com/FRmazda1.htm
or..any muffler shop should be able to make one... a couple of flanges, have some pipe bent and thats it.

 

Good Question

(thanks for stealing my spotlight)

Just joking

 

Just get this thing : http://racingbeat.com/FRmazda1.htm Under exhaust components...look for the cat replacement pipe,
or..any muffler shop should be able to make one... a couple of flanges welded onto a pipe thats bent to shape and thats it.

 

Looking at the Racing Beat exhaust, you'd get more power without the cat - less restriction.

 

hey guy's a bit off topic but i was looking at the manual and it didn't say how many cylinders my 83 rx7 has. Can ayone help me out?

 

Your RX-7 has 9 cylinders... brake and clutch master, clutch slave and six lock cylinders.. oh, you mean the engine? The engine has no cylinders.. that's why it's a rotary engine.. ::

--Danny

 

i was joking

But seriously, what do you think would be harder to do, remove cats and make replacement exaust, or hollow out the cats, cause i heard that hollowing out the catrs is a bitch

 

My cat was easy as hell to hollow out, took about 5min tops. But, my cat was just filled with carbon junk, as it had been ran without an airpump until it COMPLETELY destroyed itself and plugged the exhaust so bad that the engine would no longer run, which was the reason I was able to get a car in great shape for only $500 I've been running with the hollowed out cats for almost a year now, I don't see any problems. I also helped my friend hollow out his cats, and they were a bitch to do, but a big hammer, crowbar, and bigass screwdriver did the job well.

 

should i just try to cut off the bolts, and replace them, would that be easiest?

 

As far as I know, most exhaust shops WILL NOT replace the cats with a straight pipe. I was told its illegal to tamper/remove emissions equipment like that.

~T.J.

 

I also have a quick question. My exhaust set-up is a Header, a Flowmaster, and a Resonator. There is a leak right after the resonator, do you think it is even worth getting this fixed.

 

Maybe for your health..lol

 

i drove my 7 to the muffler shop with open headers... told em to put a straightpipe over the axel into my muffler... they did it for 120$ cdn al the welding and fabbin aswell
it sure was loud with open headers... but it is almost as loud just with a cleaner sound lol

 

I totally agree, and have experience on that. Hack, they won't even work on your car, if the cat is not even on. Well, at least here in CA

 

Why not hollow out the cats? 2000/07/29

Hollowing them out will make your car louder. A catalytic converter functions secondarily as a muffler. An unmuffled Mazda rotary is naturally very loud compared to a boinger of equivalent output. It usually needs all the muffling it can get.
Catalytic converter modification or removal is illegal in most areas, except on cars used only off of public roadways.
Emissions testing requires their presence in order to pass.
New ones very are expensive, and in many areas, it is illegal for used parts vendors to sell you a used one. Economically speaking, it makes better sense if you are seeking a modest performance boost to unbolt the cat and install a resonator or replacement pipe in its place, saving the cat for reinstallation at such time as your car, or maybe a fellow rotary owner's, must pass an emissions test.
A stock Mazda cat is difficult to hollow in a manner that produces significant flow advantage over a good condition stock cat. When a stock cat gets "plugged up", it is generally only the inlet that is blocked. The blockage is usually at least as easy to remove as it is to hollow out.
Rarely will a hollowed cat flow as well as a straight piece of pipe, or even a resonator.

 

I agree, I also used a resonator!

 

Here in Minnesota THERE IS NO EMISSIONS TESTING!

(does a happy dance)

So, what you're saying is, the best bet is the straight pipe, or resonator, in place of the cat, or hollowed out cat for power?

 

I put in my own strait-pipe, after 3-4 attempts to get a shop to do the work.... no go.... They're quite **** about illeagal bypassing of emmission equipment here.

Its not that loud, as long as your muffler is ok. Now headers and a strait pipe, that's probably a different story. A resonator/presilencer would definately do the trick.

 

I have a rb header, custom strait pipe exhaust, and the stock muffler and it is loud as hell at cruise speed and even louder at wot. I would definately recomment the presilencer (expecially if the cops in your area like to pick on loud cars)

I am running a 17" flex fan and a Holley red fuel pump, both of which are loud as hell and I cant hear them at all at 60 mph in 5th (about 3500 rpm)

peace

 

Dont hollow the cat, youll have an expansion chamber. straight pipe it

www.testpipe.com

 

i've been running a hollow cat for about 4 years now with no probs. its a great and cheap way to boost horsepower. it's so easy that a monkey could do it. unbolt cat. mangle insides w/ long screwdriver and hammer. shake out the crap. reinstall. if you're on a budget, hollow it out. if you've got a few bucks to spend, replace it with the RB pipe. if you've got even more cash, get the whole RB system.

 

I wont argue that it works. Its just better to pipe it. And its a cheap upgrade.

 

You can do whatever you want to a rotary exhaust wise, and it wont be loud. But when you get rid of your cat, its hard to keep it quiet.

I have a Flowmaster and a resonator, and my neighbors bitch about it.