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Thread: Emissions-legal catalytic converter upgrade

  1. #1
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    Emissions-legal catalytic converter upgrade

    Not sure how many will find this interesting, but there is plenty of evidence restriction after the exhaust manifold (pipes and cats) are a source of horsepower loss. Short of installing long-tube headers, the best you can do is open up the exhaust including the cats. We have 2" from the factory, although it does choke down to 1-3/4" after the rear cats. Even stock engines benefit from less restriction here. Although I can't find the article where somebody did a before/after dyno with exactly this experiment, it was worth about 20 HP on a bolt-on only engine. Modified would be worth more.

    As more states adopt the restrictive CARB rules, knowing how to live within the rules without re-configuring your car every few years could be useful information.

    If you look at the CARB catalytic converter database you find a list of aftermarket converters that have been officially blessed by application. There are bolt-ons assembled with pipes, but what we want are larger cats with an EO number for our cars. Turns out AP emissions makes #761015 which is approved under CARB EO D-754-1. This is a 2" cat, and the same part number is approved for front and rear locations. However, they make the same part in 2-1/4" and 2-1/2" under the same EO number! these are part numbers 761016 and 761017 respectively. I need to confirm, but I believe the numbers stamped on these that are checked at inspection (if your cats have been replaced) are the EO numbers, not the manufacturer part number - the same for all sizes.

    So buy some stainless mandrel U-bends from Burns stainless (press bends are verboten for horsepower), make sure you hire a skilled exhaust guy, and go to town!
    Lifespeed

    2004 Silver Birch Marauder 130K miles
    Wilwood Aero6 F, NMDP R brakes, Penske 7500DA shocks, Hypercoil 600lbs F and Grand Marquis R air springs, Addco tubular sway bars, Metco control & Watts, 31 sp axles, Stainless Works cat-back exhaust, Lidio tune, American Racing AR883 9.3" 50mm F 10" 59mm R 20" wheels, Pirelli P-Zero 265/35-20, 275/40-20 tires

    Coming soon: Livernois 5.0L stroker, ADTR/Vortech V2 intercooled SC, Silverfox trans and Circle D converter

  2. #2
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    Good info. Now trying to find a skilled exhaust guy. Oh wait, thatís me..


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  3. #3
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    justbob,

    Are you relocating to northern CA?

  4. #4
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    These aren't high flow, right? Just allow for bigger pipes?
    2003 Mercury Marauder 300B (Daily Driver)
    1988 LTD Crown Victoria S

  5. #5
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    Quote Originally Posted by 88LTDCV351 View Post
    These aren't high flow, right? Just allow for bigger pipes?
    I didn't see flow rates published. CARB actually dictates mfg's can't advertise improved flow. Might have to call AP Emissions. That said, the before/after Dyno on the Marauder cat/pipe upgrade was done with stock Mustang cats, not "high flow" aftermarket. I think they may have been 2-1/4". It could be the pipe size of the cat is important. The cross-section of the catalyst is far larger than the pipe.
    Lifespeed

    2004 Silver Birch Marauder 130K miles
    Wilwood Aero6 F, NMDP R brakes, Penske 7500DA shocks, Hypercoil 600lbs F and Grand Marquis R air springs, Addco tubular sway bars, Metco control & Watts, 31 sp axles, Stainless Works cat-back exhaust, Lidio tune, American Racing AR883 9.3" 50mm F 10" 59mm R 20" wheels, Pirelli P-Zero 265/35-20, 275/40-20 tires

    Coming soon: Livernois 5.0L stroker, ADTR/Vortech V2 intercooled SC, Silverfox trans and Circle D converter

  6. #6
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    BRG Racing highly recommends:
    http://www.spdexhaust.com/
    Ask for Chris!


    *************************

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