Questions about exhaust.

thatsnninety5 · Nov 29, 2023

On my 98' GT, I have BBK Shorty headers, I HAD a BBK Catted X-Pipe but unfortunately after further research the guy I bought it off of said it was for 79-04 but its only for 79-93, I only paid $40 so not that big of a deal. But I took the catted x-pipe off and decided I want to run no cats' and just flow master 40 mufflers. Is there a downside to no cats?

Mustang5L5 · Nov 29, 2023

It's louder and might stink a bit. Your check engine light will come on unless you run MIL eliminators, and depending on state/region you may not pass inspection and might get hassled by the cops.

thatsnninety5 · Nov 29, 2023

Mustang5L5 said:
It's louder and might stink a bit. Your check engine light will come on unless you run MIL eliminators, and depending on state/region you may not pass inspection and might get hassled by the cops.

The pipes coming from my headers for my exhaust the “down pipe” has an o2 sensor and it is before the cats. Will that still make me be in need of an MIL Eliminator?

Mustang5L5 · Nov 29, 2023

thatsnninety5 said:
The pipes coming from my headers for my exhaust the “down pipe” has an o2 sensor and it is before the cats. Will that still make me be in need of an MIL Eliminator?

I am unable to tell you. Try it first. If your CEL comes on then you'll know you need to get a set.

wmfateam · Dec 5, 2023

There should be a pre cat and a post cat o2 sensor. That is how the computer can tell if the cat is working. The second, or downstream, should have been on the x pipe after the cats. When the computer sees no change from up stream to down stream, it will throw a code that would prevent the car from passing an emissions test if it is needed in your area.

ctandc · Dec 5, 2023

FYI the MIL eliminators are essentially spark plug anti-foulers. It's a metal piece that screws into the hole in the exhaust pipe, after the cats, where the O2 sensor goes. Then the O2 sensor threads into the piece you added. All it does is move the O2 sensor further away from the exhaust stream so it doesn't toss are code for cat converter efficiency.

Not sure where you live / drive, but if you have annual state / safety inspections, odds are it will fail if it doesn't have cat converters on it. You'll have to find a used off road x or h pipe, since the EPA cracked down on those being sold new now. Unless the cats are clogged / malfunctioning the power gain is minimal at best. It's going to be a bit louder.

Slice · Dec 6, 2023

I have a 1996 GT convertible that I bought from an enthusiast. I bought it with all the cats already deleted, it just has an H pipe and then straight pipes all the way to the back with Flowmasters. It sounds fabulous. We don't have annual inspections up here in Toronto Canada and my mechanic was very friendly to me and gave me the safety certificate. I don't get any smell, there's no check engine light and it runs really well. The O2 sensors have been removed. Why it all works I cannot tell you but I can tell you from my example that it can work well.