This is funny stuff. i have lt headers with the cats, but live in NJ where they do both visual and sniffer inspection so had no real choice to pass emissions.

 

I will admit that the oem substrate-style catalytics used on most American cars at this time were more restrictive than the oem metal-spiral-style (you might know these as high-flows) my old Lexus used of that same time.

The substrate styles also mute sound more than the spirals (or high flows) which look like a bunch of straws running parallel to each other. High flows are the best best, but I would take the GM substrates over no cats at all.

Even then, the most difference I've read was 12rwhp with no cats on a C5, and that was a radical ported heads/cam setup. Makes sense that in 2001 they added better flowing manifolds, but had to add accompanying pre-cats because of emissions. The older air-pocket design was getting expensive to make, but had good cat-heating characteristics. They changed this to cast iron, which flowed better, but the power only went up 5hp according to GM, because of the addition of pre cats. I also realize cams were changed and so on though. I think they went to less lift but closer LSA to make up for the torque loss while having less valvetrain wear.

Maybe you'll have to experience it first, to not like it. I'd really recommend trying to find someone with that setup though and checking it out.

(Ill edit this later if needed)

 

I have never had the problem with running no cats and stinking like fuel. You can smell a little but it wasn't like it was dumping raw fuel through the exhaust. Maybe its in the tune?

My last blown C6 had cats.....they would stink. lol

 

I agree.
Even with a very sharp tune in my previous C5, I could still smell exhaust inside the car during a cruise and my clothes would smell like exhaust.
I ran these in 3" ID (ran 3" exhaust) and you could stand behind the car when it was running and barely smell a thing.
Made a huge difference.
These are a metal foil catalyst, flow through design –200 cell per sq in.


https://www.ebay.com/p/Catalytic-Con...9225/219113553

OP,
Try the car without cats and see how you like it.
It doesn't appear to bother some people.

 

How did the install go on these?

 

Yeah, any small amount of cats that can catalyze that carbon monoxide and burn extra raw fuel goes along way in terms of the crazy amounts of gas smell. I couldnt believe how much my shirt smelled, and I would smell it all day while I was at work.

 

It went well lol Heres the page: http://www.superchevy.com/how-to/exh...9-c5-corvette/

JBA has sets for 1997-2000 models, and then the 2001-2004 models.

1997-2000 part numbers:

Natural steel - 6817S
Ceramic coated - 6817SJS
Titanium coated - 6817SJT

2001-2004 part numbers:

Natural steel - 6818S
Ceramic coated - 6818SJS
Titanium coated - 6818SJT

 

Thanks

 

Why follow the law if no one is looking? If you don’t agree with the laws in your state and think they don’t apply to you, I say go for it. My kid is totally fine with people polluting more than they have to so no need to worry about future generations. I mean we have Corvettes so aren’t we kinda entitled to do what we want? No Cats. I’ve already taken the seatbelts and airbags out of car to reduce weight.

 

You must live in California. If not, you should.

 

Plenty of people here don’t have cats. If they don’t ask for opinions about how to break the law, its really none of my business. You asked how you could break the law and not get caught. Sorry if I can’t cheerlead that. It’s a finer point.

 

I also live in PA - Only 2 Counties have a Sniffer test for emissions - Philadelphia & Pittsburgh. There are only 4 other counties (I'm in Blair and that's one of the 4) that have 'emission testing' using the Gas Cap method (A total JOKE). There is a bill out now to eliminate the Gas Cap test all together and it will probably pass. I do agree with the 'less than 5000 Mile' exemption. It is a real thing in PA
I will be running Cat-Less when done modding my car. If I hate it I can always add em and re-tune for them

 

On my track day C5 Z06 I kept the stock exhaust manifolds and titanium exhaust but removed the cats using this Magnaflow piece that is no longer made:
https://www.summitracing.com/parts/mpe-15479

The only reason I removed the cats is it gives a 14 lb weight savings and in my mind the cats make the exhaust gases hotter. The hotter the exhaust the more heat soak the trans and rear end get because of the close proximity of the pipes.
I do not think you'll see enough hp gain to really make it worth the swap if that is what you're after.

The sound is not much louder than stock except at full throttle....maybe just a little louder at cruise. Headers really are what help make more noise, especially without the cats and adding aftermarket mufflers.

 

One could probably save more weight too by getting headers, to replace those heavy cast-iron manifolds. (Cats have a lower center of gravity too. Changing the headlights to fixed would also reduce weight.)

The only way to measure the temperature difference between cats and no cats: do before and after tests with a temp gun on the portion where the pipes go over the axles.
But more importantly: to measure the temps of the differential and axles before and after.
You'd probably also have to use a fan to simulate how the heat is effected when driving fast on a track.
Then we are talking about the dispersion of heat through a large surface area over the entire exhaust from the cats backward towards the muffler, so I don't know if there would really be much extra heat at all.

 

Regarding the fan experiment, there is no way to replicate an average speed of 90 mph under the car (at least not feasibly for me). Also, the car has to be under load....just revving the motor up to 5000 rpm is not the same as 5000 rpm under high load conditions.
Although I didn't check the before and after temps of the actual pipes since it would require me to hook up sensors, I have an Edge CTS2 monitor that allows me to data log the transmission temps (what I actually care about). The engine is 100% stock except for a cold air intake. I run R-compound tires with full coilover suspension, monoballs, aggressive alignment, etc. The cat back pipes are wrapped with DEI "Titanium" (lol) header wrap for both cats on and cats off data runs. During warm 90 degree days, the transmission temperatures stayed below 250 degrees without cats and got just over 265 degrees with the cats in place.

The other issue is the transmission also seems to get heat soaked from the over axle pipes between track sessions. You can see on the data log that the transmission just starts hotter every session as the day goes on. That was my theory on the header wrapping of the pipes....try to keep the heat from radiating into the trans and diff when sitting in the paddock.

Unfortunately I have no idea how hot my diff is getting. If I keep this car, I will probably do a diff/trans cooler in the future.

 

I too live in PA and exercise the "keep it under 5000 miles" loop hole!