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Discussion Starter #1
Taking out the cat seems like where some cheap hp can be made, but I have some questions about it, namely the noise factor.

Setting up a hypothetical question here; if I were to take out the cat on my stock exhaust and replace it with a test pipe, how much louder would the exhaust note be? As loud as a Borla? 50% louder? Now if I replaced the cat with a resonator, how much would that decrease the noise? Would I see any hp decrease?

I'm soon planning on getting a custom exhaust put in, with custom 2.5" mandrel bent aluminized steel, and probably an Arospeed Bomb tuneable muffler. Of course I'd like more power, but I don't want to piss off my parents if it's too loud. Should I take out the cat and put a 2nd resonator in there? Thanks.


BTW - Catalytic converter emissions have been shown to contribute to global warming, so don't give me any crap about deciding to take it out.
 

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I've taken my cat out... First I had just straight pipe replacing it but it sounded like shite. Not loud but just like a stupid whirring or something like that. I don't know how to say that better. I recommend cat replacing resonator. Don't worry I don't think that makes your car too loud.

About those xtra hp; I haven't dynoed so i dunno. At least what I noticed, it makes the car a little more responsive to throttle and makes a slight pike in the 5000 rpm. I don't remember that it would have been noticeable when the cat was on. (I have 2.5L V6)

Hope this gives you some information ;)
Mici

Ps. I have 2 mufflers on my car and it sounds nice but not loud.
 

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You're car has a newer cat on it? It has little to no restriction at all, and by increasing the diameter of your exhaust by that much may actually harm power on a NA car by lowering the compression in the exhaust line. I can get specifics from my mechanic, its been a while since I've read up on this. Anyway, removeing the cat doesn't improve performance on the dyno, unless you count the pound or two in weight savings.
 

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Taking the cat out you will gain 4-5ft/lbs tourqe and 5 HP throughout the RPM curve. It has been dyno just can not remember the site. I have removed mine my exhaust has 2.5" pipping from the collector pipe then 2 race res flowing to a dual 3.5" straight through muffler! The gains are most felt past 5000RPM right to redline pulls very hard.
 
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