Gutting Cats How-To

[saytagf]

Where is this o2 sensor located and does it need to be replaced/upgraded or can it be disabled? If so how and if it needs to be replaced what kinda cost we talking about here? Also can the factory gaskets be reused or are they too fried? Forgive my incompetence on the issue.....lol

[misterp]

So by gutting them using the mention method They CAN"T do damage to the engine?? Is there any other mods that are contingent or required by me gutting the cats....I.E Mr.P mentioned something about o2 sensors?

Catalytic Converter 101:

 

Pros: Cats help clean the exhaust of excess hydrocarbons in effort to reduce smog; running cats gives you a warm fuzzy feeling knowing you are helping the environment and complying with federal EPA laws. Modern era cats perform well and are not a huge hindrance to power or mileage.

 

Con #1: Cats slow heavily modified trucks about 0.10-0.15 seconds in the 1/4-mile

 

Con #2: The most common problem with cats is that they do not survive on heavily modified engines running rich fuel mixtures. Forced-induction and nitrous engines must run very rich fuel mixtures at WOT to avoid melting pistons and valves, and this exhausted extra hot unburned raw fuel makes it's way to the catalytic converter where it is combusted; if this continues for long periods of time (more than 10-15 seconds) the cat can become so hot the innards melt (think 1400+ degrees) and turn into a complete obstruction. And driving long enough with plugged cats will cause engine destruction.

 

Con #3: Cats will not handle leaded or racing gas because these fuels contain extra chemicals that coat the innards of the cat rendering it useless (aka "fouling") AND also plugging it up solid. And driving with plugged cats long enough will cause engine destruction.

 

Con #4: Cats will not handle octane greater than 95 (race or "other" gas) because these fuels burn so slowly they are still combusting on their way out of the cylinder (!) meaning a lot of raw hot unburned fuel finds it way into the cat to be burned, again if this happens in enough quantity it will cause the cat to have a runaway combustion, melt the innards, and again plug the exhaust.

 

Con #5: Cats will not handle handle aftermarket cams which are designed with a lot of overlap, as this type of induction will cause a lot of raw unburned fuel to go right out the exhaust valve and into the cat for consumption (why else do you think "lopey" cams get crappy mileage LOL). And we cannot have a burned-up, plugged-up cat...

 

Con #6: Cats will not tolerate some header designs - for a catalytic converter to work it must be hot, but not "too hot", and this means that if your aftermarket headers allow too much heat to leave the exhaust stream (very thinwall/lightweight tubes, or ceramic coated) or if your catalytic converters are relocated too far away from the engine they will be too cold to work properly (they won't "light off") and will slowly plug/foul with hydrocarbon soot and given enough time become completely obstructed. And a constipated cat will cause a very unhappy engine and after a while engine damage.

 

Con #7: Cats do muffle the exhaust note (some folks will not view this as a negative)

 

Aftermarket high-flow catalytic converters may offer less restriction, but will still have the same pros/cons and you can easily kill a set of $500 high-flow cats on a FI or nitrous motor.

 

Removing cats will in no way harm the engine. If you decide to "gut" the cats the stock collector joint uses a trick compressed metal ring gasket/seal available at the dealer for $9 per side (get two).

 

O2 Sensors:

 

The truck is equipped with 2 oxygen sensors on each side of the engine (four total), located in the first 3-4 feet of the exhaust system near the engine; these are easily seen from under the vehicle, on the driver's side you will plainly see the first sensor near the joint between the exhaust pipe and the manifold, the second sensor is screwed into the exhaust pipe a few inches after the catalytic converter. The forward/front oxygen sensor is used by the computer to tell real-time how rich or lean the engine is being fueled, the second sensor is used solely to tell if the catalytic converter is functioning correctly.

 

So, when removing the catalytic converters from the exhaust system the rear O2 sensors will see a rich condition (i.e. lack of oxygen) and report a malfunction to the coputer, and the dashboard engine malfunction light will turn on. To work around this you can:

1) program the computer to ignore the rear O2s (preferred);

2) install "O2 simulators" in place of the two sensors, but I have heard some don't work well plus they cost like $25 each;

3) strap the rear O2 sensor onto the top of the exhaust manifold (with a band clamp???) - I admit I haven't done it myself but have been assured it works a treat as the O2 sensor is sufficiently heated by the manifold and sees clean (hydrocarbon-free) air so it's happy.

 

Air Pump (non 6.0L trucks):

 

If you are working on a non-6.0L motor you will also see an air pump blowing fresh air into the exhaust manifold(s); this is for the benfit of the converter and once you remove the cats you are also free to take the belt off the air pump (or remove it outright) - you will gain 3-5 hp, a tick of mpg/economy, and have one less noisy accessory underhood.

 

Recommendations/Guidelines:

 

* If you desire a max-effort track vehicle and are running faster than mid-13s and are trying to gain another tenth in the 1/4-mile then remove them.

* If you are a forced-induction junkie and are always in the boost for long periods of time, remove them.

* If you are a nitrous user and are always on the gas driving around town, remove them.

* If you are running a rowdy cam with a lot of overlap that sets off nearby car alarms, remove them.

* If you want a little more "crackle" in your exhaust note, remove them (it won't sound louder, just have more "crackle").

* If you have modified your engine enough that it required larger fuel injectors, you have probably modded it enough that you should remove them.

 

ON THE OTHER HAND -

 

* If the engine only has bolt-ons (CAI, headers, exhaust, etc) and is running the stock cam & heads, leave them on (not enough gains to feel it and justify the hassle).

* If you have to submit to exhaust inspection (tailpipe sniffer check) then cats will be required or your vehicle will most certainly fail its emissions check.

* If you think it is a possibility that you would sell your vehicle it is best if all federal smog equipment is functional when you sell it, in some states it is implied that title transfers are contingent on the car passing a smog inspection, in California for sure it is the seller who is responsible for the vehicle being smog compliant at time of sale, not the buyer. So my point is, if you sell a vehicle without cats you may later find yourself stuck unable to sell a smog-bastard without first fixing it or taking a huge hit on the resale price (consider yourself warned).

 

Mr. P.

 

Edited December 7, 2007 by Mr. P. (see edit history)