smog question

[Bigstang1]

In theory, if i made an h-pipe OUT OF cats, i could get almost anything to pass correct? My friend mentioned it to me and i am just curious if would work or not. anyone tried it?

 

[Daggar]

The catalyst has to be able to properly function. Not all catalysts are created equal. There is also no catalyst that will make up or mask a poorly tuned motor.

So long as there's no visual inpection you need to pass, it could work.

 

[Michael Yount]

The exhaust actually needs to flow through the cats for them to be able to catalyze the chemical reactions that clean up the emissions. I'm assuming what you mean is to put a cat IN BETWEEN the two exhaust pipes on each side. The problem with that is that very little of the exhaust will actually flow through the cat. The H-pipe allows pressure pulses or waves to equalize between each side of the exhaust -- but not that much flow actually occurs through the H section of pipe. So a cat there wouldn't work very well at all in my opinion.

You simply have to pony up the $ for high flow cats. Many tests have been run -- the appropriate high flow cats for your system will do a great job cleaning up the exhaust, quieting the exhaust and cost you virtually no power at all.

 

[Bigstang1]

No i did not mean put a cat on the crossover section...that wouldnt make sense because there is no flow there. Im talking about the leangh of the h-pipe weld cats inline with eachother. just an idea

 

[Autobodypro_1]

Yeah, I did it. On my El Camino with a built 350hp 355 SBC I used dual HP Cats from Jegs and had a custom 2 1/2" exhaust with flowmasters. Like the man said before: cats won't cover a bad engine or state of tune. On my 355, I used a Comp 268 cam and a Holley 600 and a stealth dual plane....had very low emissions.

 

[Euphoric306]

there would be no point... the build an h-pipe out of cats would be so restrictive that whatever power you're trying to cover up would be wasted trying to push exhaust gas through, what... 18 cats?

 

[Bigstang1]

Obviously it would be restrictive, it would be for the soul purpose of passing the test then coming right back off. It wouldnt be on the car every day.

 

[Euphoric306]

oh... oops

yea that might work, but again make sure they dont lift the car up and check underneath