I have stock 1991 z28 besides a 3" cat-back exhaust. I still have the dual cats on the car but they are gutted.

I'm just looking to pass emissions and want to know the easiest/cheapest way to add a cat to pass as I'm going to be re-doing the entire exhaust later and don't want to waste money on exhaust components that I'll just be replacing later.

I was thinking I could just get a 3 inch slip on cat and put it on after the Y-pipe...would that work? Or is that too far back to get the cat hot?

Any ideas/suggestions appreciated.

 

You could buy 2 hi-flow cats to put on for now & reuse them when you redo your exhaust.

Or go ahead & buy headers with a single y-pipe & a hi-flow cat & put that on now.

 

Wouldn't I have to get the two hi-flow cats welded in though? With the way the exhaust curves into the cat it doesn't leave much room to slip fit and use clamps.

I'm not sure though I've never used slip fit exhaust that's why I'm asking.

 

If you think your gonna change.....Plan ahead & put bolt-on flanges on them. Then you could simply unbolt them & put the new stuff on, with flanges.

 

Exactly! Put flanges on the cats and then get them installed on to the new/old setup this way so they can easily be removed later down the road if needed.

Now here's the bad news.....why did you fail? Reason I ask is because if you put new cats on, depending on why you failed to begin with, you may nuke the new cats. Then there goes $200 down the drain. Before you go a drop a chunk of change on your cats, take a look at the car to see whats going on first. Tucson's standards are very similar to Phx and I have gutted cats on my Z, I've never failed emissions and have passed with flying colors every year.

Maybe spend the afternoon doing a little tune up and you'll probably be ok.
1. Change the plugs if they haven't been changed recently.
2. Change the fuel filter.
3. Change the O2 sensor.
4. Take off the throttle body and clean it out real good.
5. Take off the runners and clean out the runners and the egr passsages.
6. Run some seafoam through the intake if possible.
7. Change/clean the PCV valve.
8. Put in a bottle of Pass Emissions stuff or a bottle of Rubbing Alcohol.
9. Get that sucka nice and warm before heading down to the emissions station.

Now if your car is in absolute horrible shape you still may not pass but I have seen all of the above get someone through with no problems. My brother has an 89 Iroc and we did all the above and would not pass. Then we did #5 and he passed with flying colors and has not failed since.

Good luck and let us know what happens.....

 

Thanks for that info. I had searched on here to see if anyone passed easy with gutted cats but could not find any solid info. I was thinking myself that I should be able to pass without cats, so that's great news.

I actually bought this car from Tucson about 5 years ago, I went with Willie to go look at it. The car passed the emissions 2 years ago just fine, but about 6 months later one of my cats broke apart and plugged the exhaust, so I gutted both cats.

I failed on all categories, NoX, CO, HC, about double over the limit for each. I did notice my car got really hot during the test, the needle went to about 240 degrees. I also put in a quart of denatured alcohol with the tank on empty and still failed. 2 years ago I passed under the limit by about half.

I think before I get the cat I'm going to go through and do your suggestions and try the test again. I actually seafoamed the car yesterday, it blew out quite a bit of smoke. I plan on doing it again tonight.

So, I'll let you know the results. I might put in some E85 for the test too.

 

Well, I failed again but did get closer. I started a new thread in Tech with more details.
https://www.thirdgen.org/forums/tech...ml#post4509170