Hiflow question

[DefiantSix]

I'm having a bit of trouble understanding why installing a hiflow cat throws a code. along with that, what exactly does the O2 sim do to make it not throw the code. And lastly, with the sim on instead of the actual O2 sensor, how does it affect your gas mileage?

With the technical questions out of the way, I also wanted to ask if every hi flow cat isntall requires an s pipe (I kept reading about hi flows and s pipes but I never really made the connection). Why and where? What's the s connecting?

Thanks in advance for taking the time to answer stupid questions

[99camaro-3.8]

Re: Hiflow question

1: some high flow cats throw a code. from my understanding a 2.5" will not throw a code but a 3" definitely will. it throws a code because it is reading more exhaust gases than allowable by the preset computer. it feels that the cat converter itself is going out or the o2 sim is broken and giving a bad reading.

2: im not positive as to what exactly the o2 sim does to stop the code but im guessing it just tells the computer it wants by giving false readings that the computer sees as good readings like everything is alright.

3: the s-pipe is connected to the end of you cat and then hooks up to the rest of your exhaust. most cat-back systems are actually s-pipe back systems. the hook up to the stock s-pipe. when getting a high flow cat you usually increase the diameter of the pipe as well. stock cat is a 3" inlet, 2 1/4" outlet and the s-pipe is a 2 1/4" diameter as well. when you have a 2.5" cat-back and replace the cat with a 2.5" high flow cat you need to change out the s-pipe or you will have a bottleneck in your exhaust.