Modifying Cat?

[cpa]

Would there be any benefit to modifying the inlet/outlet on a stock 96 GSR cat? For instance, a 2.5" in/out to match to a custom cat-back and header? Is the chamber in the cat also cramped down? Is the cat material in an aftermarket cat really any higher flowing or do they flow more simply due to their size? If this would work, it's cheap and would be an easier fix for the O2 sensors and is actually legal. just curious if anyone has done this or any thoughts.

[4drsleeper]

I'd like to know this info as well.

[Zeus]

I believe it is illegal in most states to modify a converter...

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1998' 4dr GSR, 8psi JRSC w/hand ported plenum, 320cc injectors, Cartech adj. FMU, Walbro HP fuel pump, TPS trick in the works, valves set to .005i/.006e, MSD BTM, B&M CommandFlo regulator, stock intake w/ITR "cool air" resinator, Greddy sp exhaust, Tokico Illumina 5-ways, ITR springs, Skunkworks 22mm rear swaybar(removed due to mount torn out at present), ES motor mounts and front swaybar bushings, 205/50WR/15 Kumho Supra 712s, KVR Carbon Fibre pads, Super blue dot 4 brake fluid, B&M fuel pressure gauge, Autometer sport comp A/F gauge in dimmer location
...

YLW 00' Type R #00-1011 with "special tuning" and 143db triple air horns

Honest officer, I had no idea how fast I was going...the speedometer only gos to 150...

[The LS Avenger]

Why not replace the whole CAT with a NEW one. I got a Car-Sound (best flowing) 2.5" in/out for about $60 through the distributor.

just a thought

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total sleeper
LS Sedan with TypeR JRSC M62 @ 6psi, Kamikaze 2.5" header, 2.5" CAT, TypeR cat-back, J&S, T.O.O catch can, etc.

[cpa]

This idea seemed strange to me, which is why I asked. The idea actually came from a muffler shop that seems to have a good reputation. They claimed (and from what I've been able to find, rightly so) that there are no CARB legal OBD II aftermarket cats. This was their alternative solution and they claimed they could do it and it would be legal as they're not actually messing with the material inside or the sensors. If they do the work and it isn't legal, I believe they're obligated to fix it, but I don't want to get to that point.

I don't know, but it seemed like an interesting idea. I haven't bothered to do the math, but a previous thread linked to flow rates for cats and while there were differences, it seemed like most of it would be explained mostly by the volume increase between models.

[Zeus]

The LS Avenger

Where exactly did you get your Carsound????

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1998' 4dr GSR, 8psi JRSC w/hand ported plenum, 320cc injectors, Cartech adj. FMU, Walbro HP fuel pump, TPS trick in the works, valves set to .005i/.006e, MSD BTM, B&M CommandFlo regulator, stock intake w/ITR "cool air" resinator, Greddy sp exhaust, Tokico Illumina 5-ways, ITR springs, Skunkworks 22mm rear swaybar(removed due to mount torn out at present), ES motor mounts and front swaybar bushings, 205/50WR/15 Kumho Supra 712s, KVR Carbon Fibre pads, Super blue dot 4 brake fluid, B&M fuel pressure gauge, Autometer sport comp A/F gauge in dimmer location
...

YLW 00' Type R #00-1011 with "special tuning" and 143db triple air horns

Honest officer, I had no idea how fast I was going...the speedometer only gos to 150...

[cpa]

The places that would put a non-OBD II cat on I wouldn't trust to touch my car. Any place that's legit in CA won't do it and I don't want to mess with trying to deal with the secondary O2 sensor, getting an aftermarket cat to fit with the exhaust, etc.