Hey Anyone,

Would having 2 or more cats back to back for a smog check worth it? Would there be enough heat for 2 lengths of catalyst to work properly? Is it wrong to modify your car with more than one cat? I want to be environmently friendly and run 9 cats back (hmm, how much psi of backpressue could I live with)

If so, I had a thought about having a removable straight pipe put into my exhaust just after my Random cat. I would take my stock cat with adapted flanges to replace the straight pipe when smog time comes.

If for any reason this is a stupid idea, forgive me I'm drunk.

And when I'm not drunk, Im just plain crazy...

 

I would think with 2 cats your car would bog like crazy and they would deffinetly look b/c the readings would probally show

 

My old 5.0 '90 mustang had 2 cats from the factory. One was real close to the manifold , called a pre cat, which heats up quicker and the other is in the usual spot. And Ya, I guess the theory works because when I smoged it I had zero COs.

 

That's Cool.

I think I will get a second cat that looks like a resonator and make it interchangable with a straight pipe or my current resonator that sits a couple of lengths behind...

 

I had an old 79 Toyota 4x4 with dual webber side drafts and a bunch of other mods and I always had the hardest time smogging it, so i made a custon mid pipe with 2 cats on it and it passed every time!!
Just drive around for a line time to makes sure they are good and hot before they test your car, also keep it rev'd up a bit while your in line wait to be tested! Good luck

 

Awesome Dude! Just what I was thinkin exactly

 

Best tip I can give you for those who are unfortunate enough to live in emissions testing land is to go for a long, hard drive before you get checked, and burn all the crap out before you try. Like others said, make sure the cat is good and hot.

 

i think RX-7 got 3 cats, i think

 

Ok. I went through this whole ordeal when I was trying to BAR my car. I had a greddy header w/ a 2.5" modified collector, 2.5" 9400 carsound cat, and 2.5" exhaust. I kept failing the 15mph test. I would drive my car for an hour before the test, but they make your car sit there at idle for the longest time, so heating up the cat did nothing. The problem was that at idle my cat wasn't getting hot enough. I was passing the 25mph test, but not the 15. I talked to a few muffler shop guys and they told me that a second cat after the original wouldn't get hot enough to do anything. I mean my first cat wasn't getting hot enough as it was at idle!!

Well I finally passed by putting on a 2" midas muffler. It was alot smaller in length than my carsound. Basically, I think my problem was that I had too big of a cat and that it was firing off. My 2.5" exhaust/collector didn't help either and my exhaust/cat was prolly cooling off too fast.

I don't know if a second cat would even do anything though. Maybe if you had two short, small cats right after each other, then they might be able to get hot enough. But on a honda, I doubt it.

Is it illegal to run two cats on a car only equipped with one from the factory?