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  1. #1

    Default High Flow Cats: Worth the Money?

    Was just wondering if high flow cats are worth the money in terms of added horsepower or should I just keep the money for a programmer and/or cams down the road? I was looking at getting a supercharger but feel the cost doesn't fit my life right now ($3800 is the cheapest I found just for the supercharger), so I'm leaning towards a DiabloSport tuner, and 4.56 gears but would like some more extra horsepower. Cams would be in the future since they involve a lot of work with the engine so I'm looking for a little more oomph that I cannot get from the tuner alone.
    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


    Not sure about the high flow cats, but I would like to know the answer to that as well. I noticed you are running 35's...I highly recommend switching to 4.56's for more power, it will make a world of difference!

    Bobby - North Carolina
    2008 4x4 5.3L V8
    6" Suspension Lift and 1.5" Body Lift
    20x9 Ballistic Jesters w/35" Toyo Open Country MT's & 1.5" rear wheel spacers
    4:56 Yukon Gears
    Hypertech Speedometer Calibrator
    Baja style bed mount spare tire carrier
    Flowmaster 40 series dual exhaust
    Recon Smoked LED tails/3rd brake lights/black projectors w/switchback LED's in the corners
    N-Fab Nerf Steps
    K&N CAI
    No Fear Pedals
    Tint, Line-X bedliner, Window visors, Rear wheel well liners
    Painted front grill, bow ties and door badges, de-"lettered" tailgate
    Powder coated front and rear bumpers

  3. #3


    Yeah, I'm definitely going with the 4.56's. Just need to find a garage that I trust to do the job and all of the needed equipment.

  4. #4

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    your stock ones are just fine, unless they need replacing leave them alone
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  5. #5
    Jr. Mechanic
    Join Date
    Mar 2010
    Blog Entries


    I know of 3 diffrent people that have tried the hi flow cats and all three of them had there check engine light come on within a few hundred miles after having them put on. I run one on my honda but my honda is old and it hasn't given me any trouble as of yet. But the car has been parked for the last year while i try and find parts for it for deer got in the way.

  6. #6


    If you're going to change your cats, just get them cut off. Either way your engine light will come on eventually. Mine comes on when it wants and goes off. What some people did, was take the O2 sensor out of the direct path of the exhaust, which means, welding on a spacer, to put the sensor away from the direct flow of the exhaust. And that also fixes the engine light, because the sensor isn't getting all of the flow from the exhaust, only a bit of it. I also have a hypertech power programmer 3, and to be honest, i would recommend getting these, before a supercharger, If you do a lot of highway driving, i would recommend 4.10 gears rather 4.56. With the 4.56 you will be reving quite high when your cruising down the highway. But it will give you so much more power off the line.
    2002 Chevrolet Silverado 1500 z71 1985 Chevrolet Silverado k10 2006 Chevrolet Silverado 2500hd 6.6l LLY Duramax
    6.5" BDS Suspension Lift Edelbrock Carb & Polished Intake Manifold & Valve Covers NAPC Race Transmission & NAPC Built Transfer Case
    EFI Live Comp Cam and Valvetrain Snow Performance Methanol Injection
    35" Toyo Open Country Mud Terrain on 18" Ion Alloy 179's Headman Long Tube Headers and True Dual Exhaust FASS 150gph Titanium Series Pump
    AirAid Cold Air Intake with K&N Dry Filter & AirAid PowerAid Throttle Body Spacer 2" Suspension Lift 33x12.50r15 Tires EFI Live & AFE Stage 2 Intake
    Pacesetter Long Tube Headers with Cats Gone True Dual Exhaust FlowPro 3.73 Gears Yukon Grizzly Locker with Mag-Hytec Cover & Traction Bars
    NGK Iridium Tips & MSD Ignition Plug Wires Baja Spare Tire Holder 33x13.5 Hankook rt03 18" XD Rims
    Innovate LC-1 Wideband o2 Sensor x2 HID's all around LED taillights and 3rd brake light
    BDS Dual Steering Stabilizers Pioneer Double-DIN Touchscreen Navigation with Two 10" Subs under rear seat
    Electric Fan Autometer Pressure, Boost, and Pyro Gauges
    4.56 Gears Airlift Air Bag Suspension

  7. #7


    The supercharger idea is basically scrapped after I researched the cost of the supercharger and the modifications to the transmission and engine that would be needed. I was leaning towards a DiabloSport Tuner because I found a site that sells them for $287 shipped and have read good reviews about the product. I don't do too much highway driving so the 4.56's seem better for me, I live in North Central, Pa so it's mostly rural area.

  8. #8
    Jr. Apprentice Silverado-Joe's Avatar
    Join Date
    Mar 2010
    Lead hill, Arkansas


    No cats gives you more power than high-flow cats.
    '01 Silverado, 5.3l Vortec, Z71

  9. #9


    Pennsylvania doesn't allow no cats :(

  10. #10
    Master Mechanic Silverado Junkie's Avatar
    Join Date
    Feb 2010
    Lead Hill, Arkansas


    Dang Pennsylvania!! lol Well you could hollow your cats out and just run a pipe threw them. It'll look like you have cats installed but you'd actually have a straight pipe threw them. It works.
    1995 Silverado,Z71, 3-inch lift,2-inch leveling kit, SkyJacker Suspension, short ram-air intake, throttle body spacer, MSD ignition coil, straight pipes

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