[Hellrot Sachin]

I'm considering a set of downpipes but (bring the flames), I feel bad about removing the front cats from an emissions perspective. With the rear cats still in place, how much of an emissions difference is there?

Thanks,

Sachin

[enrita]

i passed emissions sniffer test with 100 cell HJS race cats in the middle. Dps are catless.

[Mr_PharmD]

I wonder if it's the same as US tho.

[RoundelM3]

There is a huge difference...but that's aside from the point that removing catalytic convertors in the US amounts to tampering with federally-mandated emissions controls. If you live in an area where they are very anal-retentive about emissions and you happened to go in for State Inspection and failed the emissions test because your car was missing part of its emission controls, it could be up to a $10K fine. It's up to you whether or not the chance is worth taking. Lots of people get away with it, but you never know when some State Trooper might pull you over and smell the unburned fuel or some other situation comes up where you're essentially "busted".

[Beemw335]

Just get cat less downpipes and leave your secondaries in place!
Most cars only have 1 cat we have 4 LOL

[805beemer]

I have Catless DP's plus the stock secondaries and have never smelled anything driving slow, with windows down. I've had a completly catless Sti and that thing reeked. Added a high flow cat after driving around catless for a week.

Will you pass emmisions, that I dont know. But as long as you keep the mid cats, no cop would be able to tell/smell

[austin335i]

Glad to see this post. I had the exact same question since there is a lot to gain from just downpipes.

To piggyback, is the throaty sound people describe a raspy or "louder" but still stock sounding tone?

[Hellrot Sachin]

Originally Posted by roundel335

There is a huge difference...but that's aside from the point that removing catalytic convertors in the US amounts to tampering with federally-mandated emissions controls. If you live in an area where they are very anal-retentive about emissions and you happened to go in for State Inspection and failed the emissions test because your car was missing part of its emission controls, it could be up to a $10K fine. It's up to you whether or not the chance is worth taking. Lots of people get away with it, but you never know when some State Trooper might pull you over and smell the unburned fuel or some other situation comes up where you're essentially "busted".

you make a good point.. how are they about these things in Texas? I was under the impression that virtually all states are doing OBDII checks, not actually sniffing the tailpipes anymore.. but either way, with my own conscience, I'd like to know if I'm causing significantly more pollution with -2 cats or if they is just a lot of redundancy built in and the rear cats are sufficient.

HRS

[Jeff@TopGearSolutions]

The front primary cats do a majority of the work. They are the hottest and the closest to the engine. The secondary are just that, secondary to get anything left behind. It's hard to answer your question without equipment used to measure emissions.

[zerep1]

The first cats are for Instant cleaning since cats need heat to work as soon the secondary's warm up they do the same amount of work an in a turbo car that the exhaust gases are usually a lot hotter that doesn't take very long

[RoundelM3]

Originally Posted by Hellrot Sachin

you make a good point.. how are they about these things in Texas? I was under the impression that virtually all states are doing OBDII checks, not actually sniffing the tailpipes anymore.. but either way, with my own conscience, I'd like to know if I'm causing significantly more pollution with -2 cats or if they is just a lot of redundancy built in and the rear cats are sufficient.

HRS

The catalysts are just that - something that causes a chemical reaction without actually participating (or being consumed) in that reaction. The cats make sure any unburned hydrocarbons from the normal combustion process are consumed and not released into the atmosphere. The chemical reaction between what's in the exhaust gases and the catalyst material cause the hydrocarbons to burn and generate more heat.

Here in Texas, some cars are checked via OBDII and some are tailpipe-sniffed. It varies by city and county. In the case of older cars in Montgomery County (north of Houston) for example, they are strapped to a set of rollers and put through a series of loads and throttle openings with a sniffer in the tailpipe to measure actual hydrocarbons, carbon monoxide, and so forth. At least - this is how it was a few years ago when I lived there. Other parts of Texas may not be quite as stringent, but if your exhaust causes people to cough and their eyes to water, chances are you may get dinged for not having the cats, regardless of what the OBDII results are.

To me, it'd be worth spending the extra money to get race or high-flow catalysts to be on the safe side and avoid any potential grief over missing emissions control components - assuming you're not talking about a track-only car. If it's not being licensed for the street, you can pretty much do what you want.

[Rotorocious]

Glad I don't have to deal with that stupid shit here in fla.
Completely Catless and I don't care. This is amurica, helllll yaaaa.
(firing gun shots in the air)

[clairvoyant]

I am always curious if I can pass the sniffer type emission test with just the secondary cats + a certain downpipe fix + car driven for 30 mintes or more.
Anyone from California care to chime in?

[enrita]

Originally Posted by clairvoyant

I am always curious if I can pass the sniffer type emission test with just the secondary cats + a certain downpipe fix + car driven for 30 mintes or more.
Anyone from California care to chime in?

Its not about driving the car 30 min. you need to drive the crap out of it so when you get there you have glowing secondary cats. The hotter the less emissions.

[Fred_Boosted]

Originally Posted by 805beemer

I have Catless DP's plus the stock secondaries and have never smelled anything driving slow, with windows down. I've had a completly catless Sti and that thing reeked. Added a high flow cat after driving around catless for a week.

Will you pass emmisions, that I dont know. But as long as you keep the mid cats, no cop would be able to tell/smell

Nice input.

I'm going to put my catless DPs on, and get a custom cat-back with hight flow cat. And add HEET when I need pass emission test. I live in ohio, its not as bad as in cali