FoxbodyKid

Hey guys, so I bought 2 electic exhaust cutouts for my fox. It has a catted aftermarket x pipe. I can't really decide if I should put it before the cats or after and just bypass the mufflers. I used to have my glass packs clamped on, and one time a muffler fell off while I was driving and I remember the sound was really weird. Not insanely loud like open headers, but still very loud. It sounded different than open headers/straight pipe with no cats. More deep (wow so descriptive) but it sounded more like a truck with a mix between flowmasters and straight pipe. If that makes any sense. So basically, dump after the headers, or dump after the cats? Only reason I'm really hesisitant to dump before the cats is that I feel it will be so loud, I won't be able to open it that much. But bypassing the cats is awesome, and the pops and crackles on decel I like. however, when my muffler fell off and I had an open cat, I could rev it out to 5k, and in between 1st and 2nd it would usually pop a massive flame that sounded like a gunshot, lol. Not sure if that would happen with cutout before the cat (basically almost open headers lol) I'll be putting flowmaster 40s on for my quiet mode. What do you guys think? I also think if I put them after the cats I would be able to drive around with them open during the day, I have a feeling before the cats will be just too much and I wouldn't get to opem the cutouts as much.

08'MustangDude

Most of the time, it's right before the cats... That's when the exhaust would be
the loudest, and least restrictive.

wbrockstar

Considering how terrible an engine has sounded when Ive started engines with only the headers installed,Im gonna have to go with the placement after the cats.Open headers are best left to the all out drag cars.I could be wrong,but placing them before the cats may upset your o2 sensor readings since youll be losing alot of heat out of the cutouts (which the o2's rely on to function properly) Another possible issue is,if an exhaust leak at a flange allows air to enter the system,triggering a lean condition at the o2's,cutouts will surely allow it also,which causes the ecm to richen the fuel mixture because its trying to bring the afr back to normal.
The ecm doesn't know that extra air came from an intended modification,it just sees the lean o2 reading & begins compensating for the additional oxygen.This wont cause a issue at wot because the o2's arent used during this time,but I can see how it might affect things at idle & possibly cruise.
08mustangdude seems pretty knowledgeable,maybe he knows whether the things listed above would occur or not???

proeagles

What wbrockstar said. It is only logical.

08'MustangDude

IT depends what he wants the cut-outs for. If ROAD driving, then after the cats.
Cutouts before the cats will set codes, for sure. He won't get any flames
after the cats... If he's looking to make a spectacle of it all, then they go before the
cats. Then back to normal for every-day driving.

Before the cats, then straight pipe the exhaust out for the noise and torching. Then switch
back to the factory exhaust for daily driving. That would not fly here in PA at all, as soon
as they see the cut-out(s), they fail the car...

FoxbodyKid

I was thinking of deq also. I live in Oregon and I know they look under the car with a mirror to see if there are cats. Can't I just say I only use the cutouts on the track or something lol? Or are they straight up not allowed anywhere on the exhaust? Thought this was murica. Probably different from county to county though. If cutouts aren't allowed at all, I guess they would fail me even if it was after the cat.

Before the cat would really throw codes? Even if it's after the O2 sensors? I have o2 sensors up by the headers almost, and then a lot of pipe and then the 2 cats. Honestly though this is such a hard decision lol.

Urambo Tauro

Cutouts before the cats could be recognized by a shop as an (on-demand) emissions defeat device. You'll have a much better chance of passing inspection with the cutouts downstream.

08'MustangDude

IT sets codes because the back pressure is not where it's supposed
to be. The cats won't get to operating temperature either, if before.

As far as passing a visual, cut-outs anywhere can fail it, depends on the
shop. After the cats, you do have a better chance of passing a visual.
They won't pass anywhere in PA if they do a visual.

mjr46

it's not gonna set codes on a fox, for 1 the eec iv does not monitor back pressure nor does any ecm, at most on some obd2 vehicles for example reduced back pressure by installing a less restrictive exhaust can affect dpfe/egr operation depending on the type of egr sytstem used, thus setting a code.......however on a fox egr is vaccum operated, as for cats not getting to operating temp, won't matter on a fox, cats are not monitored........as long as cut out is in a aftermarket pipe down stream of the o/2's it'll be fine.....in fact there is no real way to put cutouts in a oem 4 cat fox set up as the 2 precats are right by the headers.