I am buying a 2007 Corvette. It's a M6, Monterey Red, 3LT, fully loaded. I'm stoked! I can't wait until I pick up the car. The previous owner has installed some Texas Speed headers with an off-road x-pipe. I live in Denver, so I need to pass emissions, and not just an OBDII scan. The owner has the stock exhaust, so worst case, I just throw that on for emissions. However, I'd like to put cats on the Texas Speed setup so that I can run them permanently.

Does anyone have any experience with installing aftermarket cats for passing emissions (sniffer)? I'm really just curious as to what cats others have used (Magnaflow, Flowmaster, no-name, etc.) successfully or unsuccessfully. I have fabrication and welding experience, so I could install them, but am unsure what cats to go with.

 

What about a TSP catted x pipe?

 

Texas Speed doesn't make a catted x-pipe for the C6.

 

 

Walk in the park and just need to pick up 2 high flow cats the OD size of the X pipe to weld into the X pipe.
Note, you only going to loss about 3hp with the high flow cats in play, and even the no name high flow cats work well.

From the back of the header collector flange, you want at least 3" or greater to the honey combs start point of the high flow cats.

To understand this, watch this video on header scavenging, and you will under stand the needed distance back from the header collector you want to keep clear so the collector can scavenge correctly


So that out of the way, measure the OD of the X pipe, pick up two high flow cats that match the X pipe size, and they will be cut in/ mounted in the X pipe after the header collector point on the X pipe.






Next on the list, it a quick check of the tune. The car will hold want to hold an AFR of 14.1 when you are not at WOT, but need to double check to tune to make sure someone does not have it running too rich at WOT that it going to fail the Denver sniffer test. The AFR should be set around 12.6 at WOT, and this will allow you to pass the Denver snog sniffer test with the high flow cats.

Also, since the car has headers on it to begin with, the rear O2 sensors should have been turned off, so no codes will get you through Denver smog as well.

As for muffler, strange duck on some of them, since they can drone like crazy. Hence drone so bad, you rip them off car inside a week. This is the reason that most will run either Borla or Corsa mufflers, since they are the known not to drone.

 

I am down in Douglas County, Castle Rock area, and I pass emissions with my high flow cats on the old Pfadt header system. I am going to swap the cats for the GESI units in the coming months, as they are true high flow, OBD-II compliant, catalytics. I am getting close to the limit on hydro-carbons at idle. All other tests are passing about middle of the window.

Edit: My car is tuned and the rear O2 tests are set to complete in the ECM. I do not think you can get any set of headers and high flow cats, even the best high flows like GESI's, to pass, as the rear O2s are in a timed event with the main O2s. The headers change the distance and timing, so very likely you won't be able to get there without tuning.

 

Not so, since you can use anti fouler on the rear OS sensors to pull them out of the exhaust stream, and this will lower the readings on the rear sensors enough that they will pass the differential readings needed between the front and rear sensors.



But since your just tricking the sensors, easier not to install them, then just turn them off in the tune.

Hence front sensors needed for the tune in closed loop, and the rear sensor just check to make sure that the cats themselves are working efficient instead.
With the Rear sensor turned off, then no codes and you pass the OBD II test that is just looking for codes alone.

 

I don't think there is a definitive on that. I have seen some cars do ok using extension tubes and anti foulers, but I have seen plenty set the codes with those devices as well. I agree on your second comment about just shutting them off in the ECM and setting the test to complete.

 

You can probably buy the xpipe with cats from Ts ask them which model might work better I run a catted xpipe on my looks

 

Thanks for the info. What cats did you run when you passed emissions? How long have you ran them?

 

I put LG Motorsports high flow cats on my 07 in 08. Still have them at 214,000 miles. No sniffer test here in N. Texas. LG did the install and tune.

You can buy their high flow cats separately online.

 

In Alabama don't have to worry about emissions, just running the low end xpipe with cats, however looks has what's called a "green cat" I assume it lowers emissions even more. The thing in Ca if they see headers you fail. Lot of guys ran ZO6 systems instead including me. With today's technology there is no reason not to run cats. I'm not a tree hugger but we owe it to each other to do what we can.

 

Good point

 

The thing with the ZO6 exhaust system on a none ZO6 car IN cal, the system is not C.A.R.B./OEM manufacturer approved for the non z06 cars, and it more like trying to get one past the Smog inspectors since it still a GM OEM system that looks stock for the car instead. To take it a step farther, on the later C6's, addtional cats where required to be installed in the X pipe, so it take it even a step father in getting one over on the inspectors. Hence you first take you car to the dealer with stock system to have the cats added so you can get the letter that has to go to smog to get the intial inspection/it on record for the cars vin, then you rip all the old system out, to now install the not so legal z06 system on a Non Z06 car.

As for not having to run cats on a C6, not so true, and it just the states that don't run a smog test that you can semi get away with pulling the cats since you will not be checked during yearly smog inspections. Hence push comes to shove, and LEO really want to have its way with you during a pull over, cats are mandated federally and they could go after you for pulling the cats in the first place.

To bottom line it, high flow cats only cost you about 4hp total and they keeps the cabin of the car from reeking of unburnt fuel every stop light.

 

Well put. Sounds like it’s catted X pipe for me

 

Random Technology has been around for decades, and makes some of the best high flow cats on the market...but they are spendy at ~$200/ea.

 

The standard high flow X-pipe Pfadt provided with that system. Not sure of the make of the cats, but guess they are Random Techs.

Random Techs are not good high flows for our OBD-II cars. The GESI units are superior, also cost double, and they are true OBD-II compliant high flows.

 

I am going to purchase some headers soon and might try the catless X pipe with my stock exhaust and see how it does. If the fumes are too bad then I will add some cats later.

 

They're 49 state legal, not 50 state...so off the table for CA cars. But in the context I was referring to; OP is not in CA, and OP was looking to add cats to his OR X-pipe on his LT setup...which also, is not 50 state legal.

EDIT: I should also mention that Random Tech makes metallic (OBD1) and ceramic (OBD2) substrate cats...so choosing the right one is important.