I have a 95 cobra and need to get it smogged, the car is all stock. However my H pipe cracked in half so i need a new one. I was wondering if i replace it with a stock H pipe will it pass smog in california?
Legally, you are supposed to replace any non-functional smog equipment with OEM equivalents. If OEM-equivalent parts aren't available you are allowed to replace with aftermarket parts. If you're talking about a used h-pipe, whether you will pass smog depends on the condition of the catalytic converters. Bad/worn parts will make you fail. I would suggest getting a replacement h-pipe (used OEM or otherwise) as soon as possible and get tested. If you fail, you should hopefully have enough time to fix the problems and get tested again.
Many shops will cancel the full smog test if you fail one part. Also be aware that California has tightened the emissions standards, so even if you passed last time you may not this time. I found this out when I went in last time and barely passed. Comparing my results from two years earlier, my emissions were actually cleaner (new cats) but the limits had changed.
Well, since Mike brought up aftermarket H and X pipes, it depends on the shop that you go to. If I remember California law, you are not allowed to remove functional smog equipment. If you bought your car without the right emissions equipment, you are then allowed to use aftermarket parts. So you could argue that replacing your broken OEM h-pipe with an aftermarket one is OK in that case. But, unless the smog tech owns a Mustang there's no way they will know if your h/x is factory or not.
Technically you're supposed to have 4 cats, but I have yet to run into a shop that counts them; they just check to see if you have cats or not. I had a GT (which I've since sold) that passed several times with a Magnaflow H pipe, which only has two cats. While catalytic converter tech has improved quite a bit since our cars were made, you do take a risk that the two newer cats may not be enough to pass the tailpipe sniffer test.
As Mike said, a cheap fix would be to try for an OEM h-pipe on Craigslist.