See this link:

http://www.coloradofans.com/viewtopi...bb2f5dc8212795

The H3 and the colorados/canyons have two cat. converters. One is built into the exhaust manifold and one main cat is farther down. This mod removes/punches out the cat in the exhaust manifold. Anyone want to give it a shot?

 

nice find CHP!!!! I'm gonna look into this in the spring.

 

wonder if the header for the colorado would work too? a single header shouldn't be all that expensive and to gain 17+ hp and eliminate the upper cat would be nice.

 

I believe that since the O2 is monitored at the oulet of both cats...you may end up causing yourself more harm than good when it comes to performance..Not to mention the eternal Service Engine Light..

 

thats why you get one of these...tricking the 02 in a gm is easy to do and these work great. I have never run a cat in any of my trucks and have passed emmisions everytime...kinda amazing when you think about it.

 

Figures..if there is a way to skin a cat another way..you'll find it..I didn't know these exsisted..cool beans!

 

best part is they are like $22 at Jegs.

 

I guess there's away around just about anything.

 

I forget the cost of the header for the I5 (~$500), but I thought it didn't make much more power than this mod.

The precat O2 makes its measurement just above the cat in the manifold (between the manifold cat and the head). The postcat O2 is after the main cat and just measures cat efficiency/storage. The precat O2 is used for engine control. This mod isn't for everyone. If you just gut the mainfold cat, you shouldn't need O2 simulators.

The tricky part is getting the manifold out because we have an AC line that is in the way and doesn't seem able to be moved unless you bend the aluminum portion . The previous Colorados/Canyons route this AC line around the perimeter of the engine compartment, over the fan shroud, and to the AC compressor.

I just looked at this briefly, but we might have to pull the exhaust manifold out through the wheelwell if the liner is removed?????

 

dont hold out on us ..got a part #