Black9TA8

I thought all cars had to be OBD II in 96', which would mean all of them would have dual cats.

ss#1230

and you know this....man!

sprfstz

I've got a 96 Z with the dual cats and was thinking about changing to a y-pipe off the headers into a single high flow cat, will that cause a problem with OBD-II?

Feenix

yes unless you get a tune for it and program out the rear 02's or get some rear sims to fool the PCM.

sprfstz

Almost any exhaust shop should have rear sims right? And is their a "best" place for mounting them? Thanks!

AlwaysCode390

What are rear sims? I have the y pipe single cat on my 96' z and I think I keep throwing my o2 sensor code. I guess I need to get them programmed out of my pcm or I need to get those "sims". Thanks---

transamdude95

My '95 came stock with dual cats, an OBD I computer, and an OBD II connector. It isn't a California car either. New York and Mass. had the emissions options for dual cats as well as California. I'm not sure where mine originated... but I don't think it was from any of those three states.

Here's a great site for 4th Gen info: http://www.f-body.org/faq/4/index.htm

91RSLT1

Will this cause the car to fail the ODBII emmissions scan?

ss#1230

not sure if you have emissions laws up there or not. but if your gonna do that you may as well just get a ypipe without cats at all (or dual highflow cats), and then get the 02 simulators so your SES light doesnt come on. you can get the 02 sims at summit racing.

if you go from dual cats to a single cat, i would think that you would loose power. i believe they got more power from the exhaust rather than the obdII programming. the OBDII is just more emissions sensative. and more complicated.

ss#1230

the sims wouldnt cause it to fail. but the sniffer test would if you didnt have any cats. or if it wasnt running as clean as it should. but you wouldnt know that cause the the PCM would think everything was fine, cause thats what the sims would be showing it.

if you tuned that code out of the pcm instead of using the sims, it would almost surely fail due to it not having that information to read during the test.

transamdude95

I'm not exactly sure why they are rated with 10 more hp than the single cat, but I think it may be because one cat is on each manifold, instead of one cat on the I pipe where it would be more restrictive... not sure because I haven't had cats on mine in a while and can't remember how it was set up. I can't see it providing 10hp though, but that's my guess.