rob96TA

I have a 96-97 Trans am and will be doing headers in the spring.

I want to make my own custom 3 inch y-pipe which will include my dual cats.

I want to stay emmsion legal.

Can I use my factory cats and O2 sensors with out any thing getting in my way or any codes being thrown. Size of cat flanges compared to y-pipe flanges.



Is there any other ways of doing this. EXAMPLE, Using one cat instead, but place 2 o2 sensors behind the one cat.

I really want to keep my 2 cats and 2 sensors and don't want to reprogram my pcm, or use o2 sims.

Has anybody ever tried this before. Please help in any way.

nateh

The stock catalysts have inlets and outlets that are significantly smaller than the 3" pipes you are planning on using, so save the weight and use 2.5" pipes if you are going to save them. If you do save them, there really isn't any point to fabbing a new Y-pipe, the stock one is good enough because to stay strictly emissions legal, you can't relocate the cats. IOW, if you want to stay letter-of-the-law legal, you need cats in the stock location. The only way to do this is with the OEM cats and shorty headers and there's no need to make a new y-pipe.

IF you want to keep dual cats and don't mind relocating the driver's side cat, you can buy a low restriction Random Tech Y-pipe with dual cats and the fittings for all the O2's. That's probably your best bet.

Putting two sensors behind one cat will likely not work because the sensors won't be able to tell which side is being monitored. If you go to a single cat, you need to convert to OBDI.

rob96TA

I want to do hooker long tubes so that means making my own y-pipe right.

Could I still fit my stock cats on their or should i get some high flow aftermarket cats.

Will this work for me and has anyone else tried this.

nateh

Hooker LT's are not emissions legal, but if you want to use them, you could put cats on both sides. This will mean a custom y-pipe. Stock cats will not work. Aftermarket cats are your only choice. Make sure you have the O2 fittings fore and aft of the catalysts. You're probably going to have some clearance problems as well. Most people who use LT's either do true duals and live with the clearance issues, or they convert to OBDI where you can use a single cat (or none). Either way, it's definitely not emissions legal.

rob96TA

These hooker long tubes have all emmision hook-ups. egr+air
Why won't factory cats work?
I could use reducers to make them fit then open it up after the cats to 3 inch.
Might get too much back pressure for going from a 4' to 2.75 to 3' maybe.
What do you think?

nateh

The driver's side cat on your car is very large and the flange is a different shape. It just won't fit where you'd need to put it if you were to go to LT's. Get up under your car and look at the driver's side cat and you'll see what I mean. You might get away with it on the passenger side because that cat is a different shape and size than the driver's.

If you are set on keeping the factory cats, leave the factory y-pipe in place and get some emissions legal shorties. If you want long tubes, get some cats that will let those things flow.

BTW, even with the EGR and AIR fittings, the LT's are not emissions legal because you're relocating the cats. Even if you pass a sniffer, technically they are still not legal, but many places don't look that closely.

stik6shift93

Around here they don't do sniffer exhaust tests on obd2(96 and up)cars they just plug into the computer and see if your throwing any emissions related codes, if you dont you pass. Simple as that, you would however need o2 simms and would need to keep the air and egr. Good luck

speedmiser

I think you'd be much better off going with shorites and high flow cats. You wont see gains with LTs over shorties if you plan on choking down the flow by running stock cats and ypiping into 3" or smaller single exhaust.

LTs, in your situation, seems like a lot of wasted money and effort for no results, IMO.