Muffler And Cat Upgrade

Discussion in 'Fox 5.0 Mustang Tech' started by NFLjunkeez, Jul 5, 2013.

  1. Currently my 91 gt stang has it's original cats and muffler. Tomorrow I'm looking to upgrade with flowmaster 40 series and Magnaflow cats. It currently has the H-Pipe. My question is... can I get away with only using 2 cats rather than the 4 that's on there? Will it screw with 02 censors and effect my computer?

    I was hoping to go with 2 cats and 2 flowmasters. Any thoughts?
  2. Any aftermarket h or x pipe with high flow cats on it will only have two cats and no you won't have any drive ability problems or check engine lights with 2, 4 or zero cats.
    NFLjunkeez likes this.
  3. Catalytic converters consist of two different types of catalysts: Reduction and Oxidation.
    The Reduction catalyst is the first converter in a 5.0 Mustang, and the Oxidation converter is the second converter. The Oxidation converter uses the extra air from the smog pump to burn the excess HC. Aftermarket converters that use the smog pump often combine both types of catalysts in one housing. Since all catalytic reactions depend on heat to happen, catalytic converters do not work as efficiently with long tube headers. The extra length of the long tubes reduces the heat available to operate the O2 sensors and the catalytic converters. That will cause emissions problems, and reduce the chances of passing an actual smog test.

    What happens when there is no extra air from the smog pump...
    As engines age, the quality of tune decreases and wear causes them to burn oil. We have all seem cars that go down the road puffing blue or black smoke from the tailpipe. Oil consumption and poor tune increase the amount of HC the oxidation catalyst has to deal with. The excess HC that the converters cannot oxidize due to lack of extra air becomes a crusty coating inside the honeycomb structure. This effectively reduces the size of the honeycomb passageways and builds up thicker over time and mileage. Continuous usage under such conditions will cause the converter to fail and clog. The extra air provided by the Thermactor Air System (smog pump) is essential for the oxidation process. It oxidizes the added HC from oil consumption and poor tune and keeps the HC levels within acceptable limits.

    Newer catalytic converters do not use the Thermactor Air System (smog pump) because they are designed to work with an improved computer system that runs leaner and cleaner
    They add an extra set of O2 sensors after the catalytic converters to monitor the oxygen and HC levels. Using this additional information, the improved computer system adjusts the air/fuel mixture for cleaner combustion and reduced emissions. If the computer cannot compensate for the added load of emissions due to wear and poor tune, the catalytic converters will eventually fail and clog. The periodic checks (smog inspections) are supposed to help owners keep track of problems and get them repaired. Use them on an 86-95 Mustang and you will slowly kill them with the pollutants that they are not designed to deal with.
  4. SAWEET! Thanks for the rapid reply. Heading down to do the install now
  5. Thanks for the info jrichker. You said "Use them on an 86-95 Mustang and you will slowly kill them with the pollutants that they are not designed to deal with." Does that mean go cat free? Not sure what you are getting at here. :(
  6. Before you purchase a catalytic converter H pipe for an 86-95 Mustang, check with the manufacturer to be sure that it has the inlet pipe for the smog pump air as part of the package. Some of the catalytic converters are designed to be used on newer, cleaner running cars that do not have a Thermactor air system (smog pump). If the H pipe manufacturer uses these in an attempt to cheat or cheap out and make a less expensive product, they will clog and fail sooner than a H pipe designed to use the Thermactor air system.

    Some states, notably California, require that the H pipe be the same construction and configuration as the one that originally came with the car. If you have emissions equipment inspection in your area, check with the local emissions testing station to find out what is acceptable and what isn't.
    NFLjunkeez likes this.
  7. thanks. All went well and it sounds great!
  8. J's not a big fan of removing the cats and smog equipment, and I respect his opinion greatly. If you live in a state that has annual inspections or smog sniffers, I wouldn't remove the stock H pipe or smog stuff. Seeing we haven't had that in Florida for over 20 years, I've removed it on every mustang I've owned. It is not going to give you more than a few HP, but it cleans up the engine bay nicely, removes some weight off the front of the car, and gives you a better sounding exhaust IMO. Some people complain about increased exhaust smell, but I've not had that problem on 7 cars. I do recommend keeping the stock parts in case you ever want to sell the car.
  9. even if cats don't last 5 years, who cares? buy another set if you have to. they aren't that expensive. car parts wear out.
  10. The OEM cat pipe has 4 cat converters, it will be very expensive, over $600. I have seen prices for new OEM equivalent units of over $1000
    AutoZone's 2 /12" high flow cat H pipe is $634.
    Steeda has a high flow cat H pipe for $400 plus shipping.
    Individual cat converters cost $90 up, and the $90 price is for just the front pair of converters, it does not take into account the cost of the rear pair of converters. Last time I checked $90 x 4 is $360. That does not take into account that many muffler shops won't fool with modifying a cat H pipe or the cost of welding if they will do the work.

    Note: Only the original 4 cat H type pipe is legal in California.
    You may have $360+ to throw away, but most of us here don't.
  11. you run 2 full cats instead of that stupid 4 cat setup ford. $360 is less than a car payment on my wifes Toyota.if someone cant afford that every 5 years then maybe they should buy a bike instead of a performance car. Cats also wear out because of fuel mixtures richer than stoich. guess what happens when you go WOT? you gotta pay to play my friend.

    as far as CA, since the youngest foxes are 20 years old now and ford doesn't make a replacement part I guess everyone in that state is screwed. we have to ASM dyno sniff our cars in metro areas in TX. if people racing their cars are that worried about cats and live in CA they are in for an expensive ride. as far as muffler shops that wont touch them, they aren't the only people that know how to weld in world. ;)
  12. Stock cats sell on craigslist for $100 to $125 all day long in great shape in my area so it's never been a concern for me personally but if I lived in Cali i'd either give up on cars or move because it seems fighting the smog police or trying to have a fast car in that state is a lost cause.
  13. I can tell you right now what that exhaust smell is. When I put the TFI module on the smell dropped down to nothing. Timing timing timing.