Cscokd

I mounted my high-flow cats right at my headers in front of the cross-pipe in an effort to keep the cats hotter and closer to my O2 sensors. No codes, so my O2 sensors are happy. Anybody think I screwed up? All the pics show the cats mounted behind the cross-pipe which I believe is the most optimum setup which allows the cross-pipes to work better.
John

hrdtopv8

Huh?? Which 02 sensors are you referring to? If the fronts then it doesn't matter wear you place the cats.. Fronts only measure air/fuel mixture right after gases exit combustion chamber..

BUT if you place the cats AFTER the rear 02 sensors then, yes, you will throw codes. As the rear 02 sensors, their primary use is to check and make sure the cats are working.

If you are throwing codes from your rear 02's then you can either shut them off with a tuning software or 02 simulator. If the fronts are throwing codes then there is something wrong with the tuning or sensors themselves..

RPO_Z06

Thats how mine is, it has to be that way for the cats to light up.
I've seen the pics your talking about but thats no longer the desired way to set it up if your running cats.

Cscokd

Thanks, I just wanted to make sure I wasn't doing something stupid. I put my cats right at my headers in front of my cross-over pipes because they will light up and heat up properly whereas further down the line they might run too cool. I eliminated my rear O2 sensors and programmed them off with HP Tuner software. So far runs great and no codes, however I also believe cross-over pipes are more effective closer to the headers and in front of the cats from a horsepower perspective. I wish Lou G. would render an opinion on this.
Thanks
John

SpeedyZ

That is exactly how I have mine installed. If your not running rear O2 sensors it don't matter where the cats goes as far as codes. The cats will do their job better up front but I think there is a "slight" power advantage to having the x-pipe up front. I wanted to use 4 O2 sensors so I put my cats up front and so far it has worked out well.

0Louis @ LG Motorsports

Z06ufgrad2002

This is exactly true.
You are forced to make a conscious decision whether you care more about hp or heating the cats up sooner. My understanding is that the newer HF style cats will light up at lower temps compared to older designs and the OE cats. So placing them further back is not so much a hinderance in their abilitiy to perform.