O2 Sensors
 

So I took my 2002 3.8 to the exhaust shop yesterday and I saw that it had 4 cats. There were 2 O2 sensors closer to the headers/1st cat and then 2 more near the beginning of the second cats. They guy wanted to cut it just before the second cats and put 2.25" piping to a small X and then more piping to 2 flow pro mufflers. My question is, the O2 sensor on the passenger side just before the second cat is actually in the cat it self so if he cuts it before that the O2 will be thrown off, he said that he will cut a hole in the pipe and put it back in there, will this work and not give me a CEL? I heard one he did a while ago and sounded ok but not very loud at idle. Would an H-pipe give me better sound? I told the guy I wanted 2.5" pipes and he said it would make it sound sick, is he right? Lastly would a 04 GT cated H pipe fit on mine? I think I am going to get the cated H pipe from a GT and run 2 flowmaster 40 or super 40 mufflers? What do you guys think?

I think you should worry less about sound and more about performance, bt that's just me lol

Why cant I have both? How am I not getting performance by going to a true dual system and opening it up for more flow? I would do the headers too but I have to pay for tuition first unless your willing to help out? How is doing a new custom exhaust sytem not giving me performance am I in the dark?

My apologies, It sounded more like you were worried about how the car would sound then how it would perform. I went 13.2@102.2 with stock headers and an open stock 4 cat h-pipe (of course that was with a 5.0, but the logic still applies). Until you really start breathing in more air don't worry about the exhaust too much. You'll spend a lot of money, getting a car that sounds like it'll run 11s and then ends up being SLOWER than stock because you've killed all yor tq by getting rid of the back pressure. Just put some magnaflows on with your stock exhaust and be done with it for a while. Put that other money into performance goodies.

If the 02 sensor is before the rear cats, you can remove them if you want, you may end up with problems come e-test time though, I'd just leave them on, you won't notice the power/sound difference.
As for sound, an H will sound much nicer, it will give you a deeper tone, more like a V8, the X will be higher pitched and sound raspy, not a fan personally, Flowmasters will likely give you a decent sound, but Imco sounds better and louder from what I've heard.
A 2.5" dual system on a V6 will likely kill some power and will surely kill your torque-especially low-end torque, a 2.25 system is more than enough for a 3.8L.

What they said.

i just looked at a set of cats today, and i think i know what you are talking about.

The 02 bung is in the cat, but it is before the "stuff" in the cat.
So if your guy put a new bung in the pipe for the 02 senor you will be good.

Yeah I think thats what he wanted to do. The O2 sensor on the passenger side is located more downstream that the driver side. He wanted to cut right before the rear cats and put in the pipes from there on (leaving the precats in). But yeah something about a bung and then putting it back in didnt trigger the CEL on a couple other ones he has done. So I think I am gonna do it and get the H pipe instead of the mini X he had done before. Does anyone know where I can get flowmaster super 40s or delta 40s for cheap?

what's the point of freeing up flow by removing a couple of cats just to cork it again with flowmasters lol.....i know, i'm a big jerk

yeah you have a point but opening it up too much would make it sound sick and i would be farting around town. The flowmasters add "control" to the noise and turn it into something worth listening too... Scores what do you recommend is a good setup for my car in terms of exhaust? If you would powder coat me some headers for free then I would think you were on to something and the other 1000's of guys with flowmasters would be wrong.

a good set up for a stockish 3.8 would be to port the stock headers (smething you can do at home for free lol), leave the stock cats, get a set of magnaflows and have a mandrel bent 2 and a 1/4 inch cat back done. It'll sound good, work good, and will be way easier on the wallet leaving money for other go fast goodies.

I'm not saying all the people running flows are making a mistake, back pressure is back pressure whether you get it from the cats or the mufflers. If I wanted to run an off road h-pipe and after market headers I'd run a set of 3-chamber flows too just to keep the back pressure up. It's 6 of one thing and half dozen of another. In my case it was simply easier and cheaper to keep the stock stuff and spend my money on bigger bangs like gears.

See this is what I am looking for...straight up answers, I appreciate that. Yeah I hear you loud and clear...So how do I go about porting my stock headers? What do you mean by a 2 1/4 cat backbone? So no mid-pipe? Just cut the existing piping after the cats and then run new piping to a set of magnaflows? Sorry for being ignorant but I need things spelled out for me to visualize it. So again no H or X pipe just straight to magnaflows and out?

You'd still be using the stock pipes and exhaust set up that came factory on the car. The term "cat back" refers to all the piping down stream of the cats. I can't remember off the top of my head what the 3.8s used, I think it already is 2.25 inch piping. If it is, and if it's mandrel bent from the factory (the bends are nice and smooth, not crinkled) then all you'd have to do is have a set of magnaflows put on. If not you'd have to order a cat back for the 3.8s or have someone make you up a custom exhaust system.

Yeah but from what I have heard, bolt on catback systems are restricting and dont really give you any performance just the LOOK. Remember I want both, it would make sense to go duals for sure. As far as magnaflows, I have talked to a couple of shop owners and they are magnaflow dealers but dont sell it cuz its crap for the mustang. I know the flowmasters are marketed really well for the mustang but again this is what I have heard and found out in my research. Plus the stock system on a 3.8 comes with a y pipe, which makes it hard to do duals properly and minmizes performance.

Personally I dont see anything wrong with cats, they produce a little back pressure witch is good. No back pressure burn out your valves.
Those new Performance cats are great there is nothing wrong with them at all....Nows its just hear say.
Just my $0.02

So should I leave my rear cats in and go into a h pipe then to 2 flows 40s

You know dude, do what you want. It's your car after all. if you're peeps are telling you magnaflow is crap they are probably telling you crack is good. Whatevs. best of luck to you and your buddies running 16s with a tailwind.