How much of a performance gain (if any) would be noticable if I were to hollow out my main cat? how would I do it if I wanted to? Just shove a brrom in there or something?

and whats up with those bonez high flow cats? are they any good? how much beter would a RB presilencer be than the bonez high flow cat?

thankks

 

just take it out, jam something through it, keep jamming it through it, and get all the honeycomb stuff out. replace cat. done.

 

Well here is what I ended up doing. My center cat was plugged up so I ended up ramming a large wrecking bar up its @$$ and busting the chunks out of it. Spent about an hour with "big birtha" the wrecking bar and cleaned it out. A broom wont do anything but leave splinters and if you have access to say a BIG mama 1/2 in drill and say a 1 1/2" concrete bit you can make quick work of this job. When you do get it all cleaned out be aware of the stainless steel bedding thats used to hold the actual catylist brick in place. Pull that out so it doesnt get caught in a muffler downstream.

Now from my experience with the empty cat the car will feel about the same or a little quicker with a little more turbo whine when it spools up, the fool behind you will hear that as well. The underside of the car however will run MUCH cooler and if you premix you will notice a little more smoke because the cat doesnt burn it off.

If you live in an area with smog testing the car will pass the visual but fail the sniff especially if you have an aftermarket downpipe or otherwise eliminated the pre cats. Im going to replace my hollowed out cat with a good Donaldson industrial engine resonator to get the exhaust note down to a deep but muted roar without the crackly sound. Son wants fart cannons but I want to keep the stealth quiet and save it for the unsuspecting fools...

988

 

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screw it look here

Why not hollow out the cats?

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.

 

im in canada. no smog tests cept for in vancouver (where I am not)

will I notice much more smoking if I dont premix?

 

from what i understand you will notice less smoking on startup if you premix. This is also if you remove the oil injectors/lines/omp. Seems these can leak into the combustion chamber white its sitting-thus causing smoke on start-up. Im thinking ofblocking off the omp because of this problem.

 

I replaced my precats & main cat with the Racing Beat presilencer/cat replacement pipe, and I'm quite happy with it. I'm not convinced that having big random chambers in the exhaust pipe is the best way to get good flow - I prefer the straight through approach of just getting rid of them entirely (preferably with a good presilencer to keep the noise down).

Then again, some people seem to enjoy insanely loud cars. *shrug*

I'm not sure how much working cat sets go for, but if you keep them intact, you can probably sell them for a chunk of change to someone who needs cats to pass emissions.

-=Russ=-

 

yeah. did you get the header too? or jsut presilencer and down pipe.

anyone know what kind of a diff the header makes? is it just sound or performance aswell?

 

I have just the presilencer and downpipe. I sadly still have the giant cast iron finned bathtub attached to the side of the engine.



I've heard that the header makes quite a bit of difference, and looking at the (stock) box with holes in it, I can't imagine anything much worse for flow. Supposedly the best option is the true dual exhaust system - headers, and totally separated flow all the way out to the mufflers.

-=Russ=-

 

yeah but if you go all dual then you have to upgrade everything all at once. this way we can do it bit by bit.


hows the performance on those High flow Bonez cats?

 

I saw a guy (not a 7) who took a cat, cut it in half, emptied out all the crap, welded it around a straight pipe, put it back on. Couldn't even tell he had done it, and luckily the emissions test values are so low in CT, he passed it with ease.

 

^^ The way to do it in my book ^^

 

i hollowed out my bonez cat bc i didnt really have the $315 to replace it..it got a little louder..especially on start up..but other than that not really..put it this way when it was intact with the cat back i have now i could set car alarms off in the mall parking lot..ever since i gutted it out i havent set any off..the only bad thing that came out of doing it was it smells like bloody hell now..so IMO i say do it to it

 

My experience, Remove the stupid thing, it weighs a ton. It will be louder, It won't smoke more, MPG will go up possibly 5 mpg.

first choice would be to replace it with a resonator
second replace it with a straight pipe

 

ive heard of shoving a straight pipe through a hollowed cat for better flow but not sure how easily it would be done. welding a split cat (like $100T2 said) would prob. be easier.

 

what really? it increases mpg?

 

knock that **** out with a jack handle or anything heavy i suggest starting the car while having it off just to hear it for a bit lol its an awesome sound

 

ok. Ive got to go buy 2 more jackstands tongiht, but after I do ill TRY to get the bolts undone on the cat. I couldnt get the muffler ones offf :P