i think this is where this should go but im not sure.

anyways on an OBDII car, can you put straight pipes in place of the cats, run O2 simms and still pass emmisions. i thougth there was no problem with this cause i always hear of people passing OBDII cars with no cats just as long as the computer is tricked. however i also heard they are supposed to do a visual inspection and a dyno test with a gas analyzer. any thoughts on this or most of all anyone have real life experience? thanks

 

If you have a OBDII car, chances are they wont do the dyno. I can't vouch for everystate, but here in New jersey they just plug it in to the computer and check for codes.

You can run the o2 simms with straight pipes and get away with it that way, but you are correct that a visual inspection is performed. So the best way to do it, is to strait pipe the cat itself, so you can get by the visual.

 

I would think any state would fail visually if there were no cat there. Regardless of sims, SES lights or anything else. What are the requirements in your area if Illinois?

I was told that NJ uses dynos, but then my folks live in Willingboro and anything goes there.

 

o. well i think my dad said when he took his 99 dakota in, they just plugged in and didnt go on the dyno and didnt even look underneath. ive heard mixed thoughts all over. i realy wanna just replace the cats because if i have to put them back on theyll still be good as opposed to cutting them up and "hollowing" them or w/e. thanks for the good response, ill see what else i can dig up.

 

Judging from your sig., your car is a 93, correct? If so, that is an OBD-1 style connector and it will have to do the tailpipe (dyno) test. I passed emissions with long tubes and 02 sims. but then again I have a 97 with OBD-2 and they only plugged into my PCM to perform their tests. It would be worth it to put those cats. back in, I am from your area(Schaumburg) so I know just how rough the testing stations are..

 

actually i just crashed my 93... anways, the new car is a 97 WS6. thats why i was asking. i know they only plugged into my dads truck so he was fine but ive heard others say there is visual too. i want to take the cats out for a little more noise. also i heard that you only need 1 O2 simm, for the passenger side, because the drivers side doesnt have an O2 sensor. this was coming from a guy with a 96 z-28. i always thought you needed 2, but as stated before my car was a 93 so i never dealt with O2 simms at all and left the stock cat on. any suggestions?

 

If you have a 97 then they are just gonna plug you in. You will need two sims. as you have a dual catalyst car.

 

thats what i thought. thanks for clearing everything up.

 

You'll need 4 simms since the OBDII cars have 4 O2 sensors(2 pre and 2 post cat). The 2 after cat O2's only report the exhaust data to the computer to trigger the SES light if the cats look like they're going bad. The 2 pre cat O2's are needed for the computer to make adjustments to the mixture. In NJ the OBDII cars get plugged in to check the computer and they do a visual to make sure you have the cats. I don't think they put anything in the tailpipe but it was hard to see what they were doing when I went through last week. So you'd probably need 2 gutted cats welded in to pass the visual so why not run 2 high flow cats, they don't rob much horsepower at all. The muffler will rob more power than the high flow cats combined.

 

i know someone with an LS1 SS with long tubes, ORY, simms and catback, he passed fine and my dad just went and passed, no visuals done at all. im pretty sure you only need 2 simms... the ones before the cats tell the computer what to do according to the exhaust, the ones after the cats make sure the cats are working if im not mistaken, so basically the simms tell the computer the cats are working, when there are no cats at all. correct me if im wrong, because i honestly am new to OBDII but thats my understanding of it.

 

Yeah, that's what I was trying to say, you need the 2 front O2's and can run simms for the rear O2's. It sounded like you weren't going to run any O2's at all.

 

no no no.lol. heres my plan basicaly. i dont even know what the exhaust looks like yet. i just no there are two pipes after the manifolds with cats. i plan on cutting the cats off, puttin in straight pipe(anyone know how big the pipe is where the cats go) and then just doing O2 simms. im being very cheap about this but i think it should sound good with a dynomax muffler.

 

does anybody know the size exhaust pipe ill need to go where the cat goes? im gonna do a pipe right there with a bit larger "coupler" on each side.

 

I believe the stock exhaust is 2.75 inches. Just an idea, maybe you could just hollow out the cats., it will have basically the same effect and they will be there in case a visual inspection is ever done on your car.

 

If you dont have cats its Illegal....now did this stop me? Nope Just Have to know the right people