Emissions Question

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Jun 17, 2005 | 12:15 AM

Dougs 90

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Burning Brakes

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From: Rolla Mo

Emissions Question

I have a 90 that has the 2 precats and 1 Big main cat. I can drop the precats as they are already gone, all they really care about is the main one here. What I want to do is a true dual exhaust, w/dual cats. Can I do this legally?
Another cat question, can they be run w/o air/egr or will this kill them?

thanks
Doug

Jun 17, 2005 | 12:31 AM

bogus

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From: San Pedro CA

legally, technically, no. The bigger question - does MO have a full scale emissions test? If they don't care about visuals, dual high flow cats with an Xpipe will work just great!

EGR is a good thing... if you delete it, combustion temps will rise an that will increase the chance of getting knock. Also, NOX is not effected by the cat, only the EGR controls that. Back to the emissions test question, if they sniff you, passing without EGR is not gonna be easy.

Jun 17, 2005 | 01:00 AM

Dougs 90

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From: Rolla Mo

No sniffer, just a visual, that is why I can get by without the precats. Apparently someone along the way determined that they did nothing and the main one did everything. So the tube that runs from the cat is part of the EGR right?
What cats do you recommend for either setup? If I cant do the duals, the freaking stock converter is HUGE!
Where does the AIR pump and charcoal canister come into play as far as emissions?

Doug

Last edited by Dougs 90; Jun 17, 2005 at 01:07 AM.

Jun 17, 2005 | 11:11 AM

Aardwolf

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From: WI

The AIR system pumps air to the cat to treat the exhaust when the car is first started. It helps the cat get goin'. It does nothing for a warmed up car. EGR only functions when cruising and does not affect the cat.

http://forums.corvetteforum.com/show...GR&forum_id=48

That thread talks about when the EGR is on. The tube on the main cat is the AIR. The EGR tube is heat wrapped on the passenger side of the engine. It goes from the exhaust to the intake.

Jun 17, 2005 | 11:28 AM

65Z01

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From: SE NY

Cruise-In II Veteran

Replacing the two pre-cats with a mandrel bent front Y and a 3-stage main cat is 49-state legal. Along with a hi-flow cat back it is worth 15-20chp; installing FL headers is worth another 15-20chp, depending on engine setup.

Here are some cat flow numbers from a prior thread on the subject:
Flow(cfm)...P/N........Mfg
220/250.....stock......2000, LT1 right/left side
327...........813000....Random Tech.
365...........6907.......Catco
400...........94109.....Carsound
535...........703000....Random Tech.

As you can see there is much variaton in flow rates from cat to cat but all were superior to the stock GM cats.

Keep in mind that to not lose any power to back pressure you need about 2.2cfm per chp. On a 300chp engine this amounts to 660cfm of flow in the exhaust system. So, indeed, once you get into the 300-400chp range you really need true duals with dual hi-flow cats.

Jun 17, 2005 | 04:48 PM

Lichen

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From: 1993 Quasar Blue 'vert Scottsdale AZ

Quote:

Originally Posted by bogus

Now you've got me curious. I have Random Tech Hi-flow cats and recently had to go through emissions. I just barely squeeked by except for the NOx. I passed it easily. I showed the results to my mechanic and he said with such low NOx readings, my cats were definitely doing their job. What's the dang deal?

Jun 17, 2005 | 05:29 PM

okinawa86vette

Drifting

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From: Las Cruces NM

Just fyi, I easily passed the texas state emission sniffer test with the stock motor, running no pre-cats and the AIR tube to the cat disconnected. Just make sure you have someone weld up the tube on the cat, so you don't have an exhaust leak.

Jun 18, 2005 | 12:39 PM

Dougs 90

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Burning Brakes

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From: Rolla Mo

more questions....

Okay thats what I thought, the AIR Pump just injects air into the exhaust to get the cold cats heated quicker. Makes sense. The EGR is cycling exhaust through the intake/manifold to dilute the fresh air charge and effectively cool the combustion temps.
A few more questions then...

1. What effect on longevity would running the cats with no air pump have?

2. Keep EGR, EGR good, but is this not effectively the same as overlap/reversion form a camshaft? Big difference being it is computer controlled and on demand?

3. For my application, ZZ4 350, going to AFR 195 heads, LT4 Hotcam possibly going bigger, superram intake, Hooker Headers 1 3/4" primaries I believe, and the Hooker Y pipe, how big should I make the exhaust pipes for the following situations:
a) the shop agrees to run a dual 2 cat setup with X pipe
b) I have to stay with the single cat

Also any pictures/specifications for already installed dual systems would be greatly appreciated as I could show it to them and say I want this.

Thanks,
Doug