# emmissions on a 3''



## hondakillerZX (Aug 16, 2004)

would emmissions go up a lot when going from stock exhaust to a 3'' turbo back and a high flow. i wanna make sure my car will still pass smog before i go through with it.


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## Zen31ZR (Mar 24, 2004)

Exhaust flow won't go up much more, unless you are also running a lot of boost through it. Tone down the boost controller to stock levels before you take it for emissions. 3" pipes don't do _much_ by themselves, its the other mods..... The bigger cat can be a problem, though, it takes longer to heat a larger cat up to operating temperature, and there is such a thing as having too big a cat. Having too big a cat is like having no cat all, if it doesn't heat up properly it won't clean the exhaust properly. Perhaps you should keep the stock cat as a bolt-on for emissions time.


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## Xorti7 (Dec 27, 2004)

Zen31ZR said:


> Exhaust flow won't go up much more, unless you are also running a lot of boost through it. Tone down the boost controller to stock levels before you take it for emissions. 3" pipes don't do _much_ by themselves, its the other mods..... The bigger cat can be a problem, though, it takes longer to heat a larger cat up to operating temperature, and there is such a thing as having too big a cat. Having too big a cat is like having no cat all, if it doesn't heat up properly it won't clean the exhaust properly. Perhaps you should keep the stock cat as a bolt-on for emissions time.


What risks are there if you just use a test pipe instead of a high flow cat all the time. How would anyone know as long as you keep the old cat and bolt it back in for emmission testing?

Note: I would *NEVER* do this. I just would like to know...


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## hondakillerZX (Aug 16, 2004)

how long does it take usually for a high flow to heat up. would a 2.5 or a 2.75 be better than a 3 on a 300zx turbo ?


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## AZ-ZBum (Nov 21, 2004)

hondakillerZX said:


> how long does it take usually for a high flow to heat up. would a 2.5 or a 2.75 be better than a 3 on a 300zx turbo ?


Should be warmed up by the time you get to the emissions place.
3" is fantasic on the stock turbo once you start turning up the boost.


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## Zen31ZR (Mar 24, 2004)

AZ-ZBum said:


> Should be warmed up by the time you get to the emissions place.
> 3" is fantasic on the stock turbo once you start turning up the boost.


Should be, but if he has to wait in line, it could cool down a lot. I've seen the high flow cats fail in similar situations, which is why I'm concerned. If he has a bolt together system, he should use the stock size cat for emissions, and the high flow the rest of the time.


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## Zen31ZR (Mar 24, 2004)

Xorti7 said:


> What risks are there if you just use a test pipe instead of a high flow cat all the time. How would anyone know as long as you keep the old cat and bolt it back in for emmission testing?
> 
> Note: I would *NEVER* do this. I just would like to know...


Depends on where you live. Some cities and states are more concerned about exhaust mods than others. The one I live in is not. 
Not to give you too many ideas, but I have seen a straight pipe with cat heat shields welded to the outside......


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## JAMESZ (Mar 12, 2004)

Zen31ZR said:


> Depends on where you live. Some cities and states are more concerned about exhaust mods than others. The one I live in is not.
> Not to give you too many ideas, but I have seen a straight pipe with cat heat shields welded to the outside......


And in some places there are no emissions, no checks, and nobody cares...heh


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## AZ-ZBum (Nov 21, 2004)

Zen31ZR said:


> Should be, but if he has to wait in line, it could cool down a lot. I've seen the high flow cats fail in similar situations, which is why I'm concerned. If he has a bolt together system, he should use the stock size cat for emissions, and the high flow the rest of the time.


Leave the engine running while in line. When the car before the car in front of you goes to get tested, hold the RPMs at about 2500-3000 for 15 to 20 seconds to warm it all back up and blow more gasses through the system.

I've only failed emissions once. And that was with a hollow cat. Even with my CM high flow cat, the AE had no problems passing.


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## hondakillerZX (Aug 16, 2004)

im in california so its more strict but i think it should still pass right? especially if i set it at stock boost before i go and maybe do a couple runs to the redline to warm it up. would the stock sized cat work on the 3'' or is there too much exhaust flow for it to pass emmissions


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## Zac (Mar 10, 2004)

Zen31ZR said:


> Depends on where you live. Some cities and states are more concerned about exhaust mods than others. The one I live in is not.
> Not to give you too many ideas, but I have seen a straight pipe with cat heat shields welded to the outside......


If he is testing on a 3 inch with a 3 inch catalytic, it would be worth heating it up like crazy prior to testing as well as running a higher quality gasoline and Techron additive. Mind you, this is all if they actually put the car on the dyno and emissions test. As far as OBD 2, it means simply not throwing codes. And if it is visual, well then its kinda just a butt fart as a 3 inch exhaust will have large inlet(s) and are obviously going to raise an eyebrow or four. And if the tester has a unibrow however, they will theoretically only be raising one eyebrow.


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## AZ-ZBum (Nov 21, 2004)

Zac said:


> If he is testing on a 3 inch with a 3 inch catalytic, it would be worth heating it up like crazy prior to testing as well as running a higher quality gasoline and Techron additive. Mind you, this is all if they actually put the car on the dyno and emissions test. As far as OBD 2, it means simply not throwing codes. And if it is visual, well then its kinda just a butt fart as a 3 inch exhaust will have large inlet(s) and are obviously going to raise an eyebrow or four. And if the tester has a unibrow however, they will theoretically only be raising one eyebrow.


Look at the year of the car. There is no OBD2.


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## hondakillerZX (Aug 16, 2004)

so you dont think a 3'' with a highflow will pass the visual test ?


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## ICP Sux0rZ! (Jan 10, 2005)

hondakillerZX said:


> so you dont think a 3'' with a highflow will pass the visual test ?


yes why woudln't it? it looks like a cat so why wouldn't they think its a cat


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## hondakillerZX (Aug 16, 2004)

it shouldnt change the emmissions too much i think im gonna do it. dont know how soon though lol thanks guys


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