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Thread: Two Cats?

  1. #1

    Default Two Cats?

    Just wondering if the '03 2500HD trucks came with two catalytic converters standard? From the pictures I have taken, it appears that my truck has two cats and I thought that was usually only needed for a true dual set-up. They were on the truck before I bought it, so I'm just trying to see if the prior owner did some modification or if it rolled out of the factory this way. Also, since I don't have true duals now, are two cats overkill?

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    2003 Silverado 2500HD 6.0L Vortec V8
    2" Body Lift
    3" Suspension Lift
    Skyjacker Hydro 7000 Shocks
    Skyjacker Steering Stabilizer
    35" Tires with 20" American Racing Rims
    Velocity Cold Air Intake
    Billet Throttle Body Spacer
    BBK Performance Headers
    MBRP Cat-Back Exhaust System
    DiabloSport Predator- Soon to be tuned by Diablew

    "Soon to be leveling-kit"

  2. #2


    yep one on each pipe before you get to the muffler.
    2004 Silverado 2500 Crew Cab 4x4, AMSOIL EA air filter, Granatelli MAF sensor, Throttle body spacer, Magnaflow exhaust (true dual to 2 in 1 out muffler), 6" ProComp lift (add a leaf and 5" superlift rear block), Bilstein shocks, 35's (Cooper Disoverer ST) and 4.10 gears, Rhino Liner, EGRUSA fender Flares and widow visors, extended stainless steel brake lines, firestone airbags w/onboard air compressor, Pioneer Avic X940BT navigation, Accel backup camera.
    1960 Land Rover Series II 88
    2001 Pontiac Sunfire
    2013 Toyota Avalon Limited (Wife's Car)
    NRA Life Member

  3. #3


    Alot of people cut off the "Y" pipe behind the cats and run true duals. There is no performance gain with this mod unless your putting out over 500hp. Most people do it for looks.

  4. #4


    That must be what happened then because there is no y pipe at all.

  5. #5


    Exhaust from 4cylinders with flow through a cat quicker than 8cylinder into 1 cat. Hope I explained that right.

  6. #6


    Basically two cats on an 8cylinder truck has better air flow than one cat on an 8cylinder truck?

  7. #7
    Master Mechanic
    KyleZ71's Avatar
    Join Date
    Jun 2010
    York and Wilkes Barre, PA


    "Exhaust from 4cylinders with flow through a cat quicker than 8cylinder into 1 cat. Hope I explained that right."
    Wow that make alot of sense, I always wondered why mine came with two cats, as well as my father's Tahoe.
    Objects in mirror are losing

    2003 Chevy Silverado Z71, 5.3L, K&N 57 series, 2.5'' Flowmaster Super 10 series dual exhaust , Corvette Servo, McNew Automotive Dyno tune, SS gauge cluster, Extang Trifecta Tonneau, Pacesetter shorty headers, Goodmark cowl hood, Sony Xplod speakers, Kenwood DDX-470 exhaust tips, 16" Ultra Badlands polished wheels, Pirelli Scorpion ATR .

  8. #8
    Master Mechanic clgoch187's Avatar
    Join Date
    Aug 2010
    Gettysburg, Pennsylvania, United States


    the 2500 hds run 2 pipes back to the muffler so no 2 cats is not over kill and they a re high flow cats, so they stock exhaust system allthough quiet is pretty good performance wise
    03 Silverado 1500
    285/75/16 BFG's
    2 Blaupunkt 10" vW1000 subs in Subthump box
    ProComp Level Lift & 3" rear blocks

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