I just had a single in dual out 40 series flowmaster installed on my 4.9l '89 installed. It's not loud enough for me so Im going to cut one of the two cats out. My question is, which cat has the o2 sensor ?

 

Neither. The o2 sensor is in front of both cats, on a small piece of piping that runs between the 2 exhaust pipes before they meet the collector. (You can see it easy if youre under the truck, look for the wire coming out of it on the drivers side of the pipe) The collector is what people think is a first cat, however it is already hollow, and is only used to conjoin the 2 pipes together. The second bulge is the cat. Cut it out and replace it with straight pipe. It won't effect your o2 sensor at all, as it is after the sensor. I cut both the collector and cat off mine and ran duals to glasspacks, and my o2 sensor still reads fine. Hope that helps.

 

We already had this arguement. On some both are cats, on some one is a resonator. Removing one or both won't affect anything on your truck except emissions. Cats are for emissions not sound, it won't sound much different.

 

Agreed. The sound won't change much at all. It's a V6! I have the same V6. You aren't going to make it sound like a badass truck with just a muffler change...

 

Inline 6, but thanks

 

try a headers i had luck with puting some headers on my old v-6 and made a better sound than the stock manifold. also aftermarket intakes(such as a cold air intake might help with power and mpg).

 

hahaha that's awesome! Shoulda had a V8!

 

If you had spoke rims, you could rig something w/ some playing cards!

 

i disagree with everyone here. cutting the 2nd cat out made a huge difference on my truck. it'll make it sound a little more diesely in the low end

 

I gutted both of mine and it only sounded slightly different but not louder.