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[6G96GT]

Curious...the 2nd cat that connects to the muffler...couldn't I remove it and then cut it open, gut it, and then weld it back together again and now I have a straight pipe basically into the muffler instead of purchasing a resonator??

what's the actual difference between that and a performance resonator?

[twolownissan2002]

Yeah but if you get caught then i think you can get a ticket for it unless you don't have to do inspection every year like us here we don't have to do anything here lol

[6G96GT]

Fortunately I don't have to have an emission test, they just do a visual to see if I have a cat, but if it's gutted, they won't know.

[Galcobar]

Gutted cats create turbulence in the exhaust stream and therefore diminish exhaust flow -- making your exhaust system and therefore your engine less efficient. Unless your cat is clogged by years of poor running conditions, it won't improve exhaust efficiency over leaving the cat in place.

Secondly, make sure you understand what a resonator actually does. It is NOT a round-body mid-muffler. It is in fact a carefully designed echo chamber whereby sound waves are bounced into each other in order to cancel them out without slowing exhaust flow. Missing the resonator is typically the reason for the nasty buzz on aftermarket or custom exhausts. A resonator is primarily meant to smooth the tone of your exhaust, while a muffler's main job is to reduce the volume. The round, straight-through mufflers so often advertised as resonators may resemble a real resonator from the outside, they are unalike in construction. Easy test: a resonator will ping like a bell when rapped, while a straight-through muffler will absorb the sound via the insulation with which it is packed.

Stock Celica exhausts have resonators under the body, not mufflers.

A good-quality straight-through muffler will reduce your volume, and the upside is that a longer or larger model will reduce volume with negligible exhaust flow impairment compared to a smaller version (with baffled mufflers, bigger meant quieter but much more impairment). MagnaFlow makes a good straight-through muffler with a smooth inner pipe and insulation composed of stainless steel wool and ceramic fibre; Cherry Bomb is 1950s technology with a louvered inner pipe (think of the effect of a hundred little scoops cutting into the exhaust flow) and fibreglass insulation.

[6G96GT]

I see, but now I am back to square one. This is my exhaust setup. I have a performance header going into a flex pipe which goes into a high flow cat that goes into another cat (stock) and then finally into the muffler. I want to replace the second cat the goes into the muffler. Do I want a resonator (it sounds like I do according to what you have written) or do I just want to run a straight pipe in place of the second cat that is going into the muffler?

I already posted about this (sorry guys) but Galcobar has brought a new view to me that I am interested in.

This post has been edited by 6G96GT: May 10, 2009 - 8:39 AM

[cardshark525]

If you wanted to do something like that look into getting a cat-delete pipe. It just replaces your cat and when it comes time for emissions you should be able to just pop the cat back in. Again though if you get caught a ticket is expensive...

This post has been edited by cardshark525: May 11, 2009 - 9:28 AM

[Galcobar]

You had an underbody cat on your stock exhaust? That's very odd for a 5SFE Celica from outside California.

Are you sure it's not the stock resonator?

[6G96GT]

It might be the stock resonator. It's still there. I haven't changed it out yet. So I should probably go with the resonator instead of gutting it. I really don't want to be less efficient. Really appreciate all the information. By the way, how would I know it is a stock resonator or a stock cat? It looks exactly like the cat that's before it.

[Galcobar]

Well, if you look up exhaust parts on 1sttoyotaparts.com it'll show you diagrams of the two designs, which would be of help.

The other trick is to rap the housing. As I mentioned, a resonator is an echo chamber and will respond loudly compared to a catalytic converter's internal honeycomb.