What is the philosophy / physics behind the two cats leading into a common third then splitting off to two seperate mufflers?

Are all three "cats" actually catalytic converters? Why are three required?
When people refer to gutted cats are all three gutted?

 

The two pe-cats were to take care of a one of the emissions components better than the old style main cat.

However, now Random Tech. makes a three stage main cat that handles all emissions quite well.

 

Don't our Vettes have two cats, then into a resonator and then out to two mufflers? (or is the resonator a cat?)

 

92-96 have 2 cats that feed into a resonator then out to two mufflers in the rear.

 

What is the function of a resonator?

 

I believe the resonators on the later C4s simply mellowed the exhaust note.

 

I thought california smog laws dictated that true dual exhaust was illegal, since CARB requires all exhaust to feed into a single cat converter, that can only be touched/moved/replaced if it is uh.. er.. broken.

Yet the mustangs and newer vettes only have two cats. what gives?

 

So...that would indicate to me that emissions would't be affected by removal of the mufflers and single resonator? I already did the muffler elim...I am wondering what will happen to the sound if I elim the resonator with a straight pipe also.

 

Catalytic converters:

When catalytic converters first appeared on cars, they weren't all that good. Originally they were pellet style with huge restriction to air flow. They also were specific to a particular contaminant.

Cars emit three basic pollutants along with water vapor and carbon dioxide. They are:
Carbon Monoxide
Unburned Hydrocarbons
Nitrogen oxides

on some earlier systems, the pre-cat (or whatever was first in line from the engine converted the nitrogen oxides into nitrogen gas and oxygen. Then there was usually a connection for an air source to oxidize the carbon monoxide to carbon dioxide and complete the combustion of the hydrocarbons.

As technology progressed, all of these reactions were able to occur in one converter. Pretty soon, the fuel management became so precise, the need for an air pump dropped off because of the oxygen supply associated with nitrogen oxides.

CARB doesn't have a hard on for dual exhaust. They just require that whatever was on the car from the manufacturer is still there. (or an equivalent aftermarket) So on cars with original dual exhaust - it's ok. Comingling of exhaust gases after the last converter will have no impact on emissions, so it's legal to modify the LT1 and remove the resonator.

There's other emissions stuff under the hood too....




[Modified by mitchcole, 7:59 AM 8/26/2003]

 

If I punt the resonator on the L98 then I am messing with the "whatever was there originally" factor...no?

 

Yes, but the resonator is after the cats. Therefore no emissions violations. However, sec. 27151CVC says that if you alter the exhaust system to increase noise, that is a violation of Calif. law. So you could be stopped if the mod. makes the exhaust to loud. Since you are not from this "wonderful" state, no problem, but for you Calif guys...... :D


[Modified by ittlfly, 6:29 AM 8/26/2003]

 

Okay thanks to all for the comments. Has anyone gone from no mufflers to no resonator? What is the sound difference? The eliminated mufflers was much quieter than I expected although I love the throatier sound...now it sounds like a corvette.

 

My trusty Haynes manual states:

"The (corvette) exhaust system was equipped with a single three stage catalytic converter until 1986, when two additional reducing converters were added, one to each exhaust pipe between the exhaust manifold and the main converter."

Clearly, they are referring to the above referenced "resonator" as a MAIN CONVERTER.

Therefore, I can't touch it...

comments?

 

Well, your '86 doesn't have a resonator; it has:
-a pre-cat in each branch of the front Y,
-a main cat behind the front Y
-a muffler in each branch of the rear Y

Depending on your local smog laws, you can replace the OEM pre-cats & main cat with a modern hi-flow main cat. If you do this go with a 2 1/2" mandrel-bent SS front Y. Having done these mods my '88 L98 easily passes Ohio E-Check dyno smog tests even in winter while running a 160 deg thermostat!

Since you are in Canada, you need to check on local smog laws to see if this is legal in your locality.

To further reduce emissions, do the cut-back spark plug ground electrode mod (details on my site) as it promotes a more complete burn of the charge.

 

You don't have a resonator. That is the main cat on your car. Do you have a visual emissions inspection? If not, rip that sucker off.

 

It doesn't seem like anyone's enforcing that rule, every ricer in San Diego has a fart can stuck on the back of his "racer".