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  • Converters or Not?

    As I get closer to needing exhaust for my 79 Chevy truck project I am considering whether I should install catalytic converters or not. We don't have any inspections where I live but I am leaning towards a custom install which may require converters (the shop may have no choice). I am looking for thoughts on two questions:

    Converters or not?

    What type (brand/model) would you recommend?
    Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
    74 Nova Project
    66 Mustang GT Project

    92 Camaro RS Convertible Project
    79 Chevy Truck Project

  • #2

    Re: Converters or Not?

    I'll let SBG chime in.. But he said his FJ has them because of spark arresting .... Buddy was here with his converter removed diesel F350, it stank compared to my son's with a converter.. My wife's buick's muffler went south, took it off to measure, drove to town to get a new muffler, made no difference muffler or not, so maybe converters, no muffs?

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    • #3

      Re: Converters or Not?

      That's a tough question. I get around it by not building anything that new. I own and drive stuff that has them, but they're all stockers, I don't have any interest in hot rodding them.

      Do you want to do what's legal? or do you want to do what you can get away with? I guess that's the real question. afaik, it's still a violation of federal law to tamper with the emissions control equipment on any emissions controlled vehicle. But I'm not a lawyer.


      My fabulous web page

      "If it don't go, chrome it!" --Stroker McGurk

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      • #4

        Re: Converters or Not?

        They really don't cost much in performance on a street driven car. People have the impression that they have infinite back pressure but (assuming the cat is in good shape) that really isn't the case - just a few inches H2O is all. As long as the engine is tuned reasonably and you run unleaded fuel they should work fine for you. As a added benefit you may be able to delete the mufflers - I worked with a guy with a Dodge PU that ran cats and no mufflers and it sounded great.

        There are several brands of generic converters (Catco is one) and so far I've had good luck with them. BTW - the Volvo has a pair that the last exhaust guy installed and they seem to wok and have held up well.

        Dan
        74NovaMan likes this.

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        • #5

          Re: Converters or Not?

          I have removed/gutted my share of converters and never a second thought.

          Then they changed something in the fuel. Certain engine combinations on todays fuel create the most horrendous stench, while others aren't even really detectable at all by nose.

          Maybe I am overly sensitive, but the smell is so bad to me that I don't even want to take a chance so I add converters when I am starting from scratch on an unknown engine. Not worth the chance for one or two $60 stainless off the shelf converters.

          Just look at the displacement of the original converter application and size from there. If you are doing dual exhaust on a 350 chevy, add a couple of modern converters from a 3.0l of some type.

          Its not perfect but certainly in the hunt as far as air-flow thru the engine.

          And Dan is right, modern converters have basically NO restriction to them.

          74NovaMan likes this.
          Of all the paths you take in life - make sure a few of them are dirt.

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          • #6

            Re: Converters or Not?

            I put cats on my FJ40 because fuel smells gives me migraines. It makes zero difference at the power level it's at and it works as a muffler. Further, where I wheel requires spark arresters and they, not mufflers, are considered spark arresters.... that said, the days of pellet Cats is long gone and with them the 'restriction' that people rightly complained about. Most don't use them because it adds expense and is one more thing that can break....
            74NovaMan likes this.
            Doing it all wrong since 1966

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            • #7

              Re: Converters or Not?

              " the days of pellet Cats is long gone and with them the 'restriction' that people rightly complained about"

              I didn't know that but I'm guessing they still get hot enough to start a grass fire. That happened to a friend of mine on the deer lease years ago.

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              • #8

                Re: Converters or Not?

                If you use converters, make sure the shop puts heat shields on both sides of them.
                You want the heat directed away from the floor and away from the transmission tunnel. you don't need them heating up the transmission tunnel and case.

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                • #9

                  Re: Converters or Not?

                  I like convertors, if staying under 10.5 to 1
                  There is weight limit games on the trucks, a great reason to throw the factory version in a dumpster.
                  their design does not promote laminar flow shaped like a pancake, and the claim of high flow is absurd.

                  I have a round low cpi high flow (49 state) in my 1996 gmc, and it even kicked off its own p0420 code. the ecm factory accepted the real high flow.
                  Previously boxer3main
                  the death rate and fairy tales cannot kill the nature left behind.

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                  • #10

                    Re: Converters or Not?

                    I guess it depends if you have a check engine light and do not mind driving around with it on constantly.

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                    • #11

                      Re: Converters or Not?

                      Thanks for all the input. I was leaning towards cats because of the smell. We notice that in the Camaro but not the Nova or Mustang which run on premium so maybe there is a difference there. My plan for the truck is to tune for 87 octane because I plan to use it as my daily in non snow season.

                      Does anyone have any specific converter recommendations? Motor is a 2003 5.3L and will have shorty headers with dual exhaust and a stepped up cam. Also keeping the factory fuel injection will dyno tune it once it is going.
                      Chris - HRPT Long Haul 03, 04, 05, 13, 14, 15,16 & 18
                      74 Nova Project
                      66 Mustang GT Project

                      92 Camaro RS Convertible Project
                      79 Chevy Truck Project

                      Comment


                      • #12

                        Re: Converters or Not?

                        I like convertors, if staying under 10.5 to 1
                        There is weight limit games on the trucks, a great reason to throw the factory version in a dumpster.
                        their design does not promote laminar flow shaped like a pancake, and the claim of high flow is absurd.

                        I have a round low cpi high flow (49 state) in my 1996 gmc, and it even kicked off its own p0420 code. the ecm factory accepted the real high flow.
                        Actually Barry - modern cats DO generate laminar flow. If you've ever looked inside a flow straightener (designed to straighten flow into a laminar flow stream) it looks almost exactly like a cat subtstrate. I've run back pressure measurements on a number of cats and they're all in the neighborhood of 2-5" H2O which is almost nothing. As SBG noted, the old pelletized cats were nasty and had high back pressure. (Interesting side note - I was told that GM developed the pelletized system because they didn't want to pay for patent rights for the ceramic honeycomb technology which IIRC Englehard owned. THAT bit 'em in the butt!). I suspect that a lot of the info you have is based on the folklore that developed around the pelletized system and that technology has been out of production for decades.

                        My guess on the P0420 code on your truck is probably from a failed substrate which can happen especially at high mileage and if the engine has run rich at some point. The cats can get hot enough to melt the substrate (especially the more common ceramic substrates) in a sustained over-rich condition. I lost the cat on my Dakota because I waited too long to change the spark plugs and the engine ran like crap for a few days until I worked out what was wrong and fixed it. A new Catco replacement, a set of plugs, and I was back on the road.

                        Dan

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                        • #13

                          Re: Converters or Not?

                          Thanks for all the input. I was leaning towards cats because of the smell. We notice that in the Camaro but not the Nova or Mustang which run on premium so maybe there is a difference there. My plan for the truck is to tune for 87 octane because I plan to use it as my daily in non snow season.

                          Does anyone have any specific converter recommendations? Motor is a 2003 5.3L and will have shorty headers with dual exhaust and a stepped up cam. Also keeping the factory fuel injection will dyno tune it once it is going.
                          Converters are rated by engine size and GVW.

                          We have the annoying check engine on the trailblazer, the stock converter was over 200. Went to the universal parts on rock auto and got one for 35 that we will weld in. Basically pipe diameter and length are the options once you get over your engine size.

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                          • #14

                            Re: Converters or Not?

                            I ran two converters on my first and second 350 S10 pickups do to having a shop make the exhaust . I really wanted just two turbo muffs . I didn't want it too quite so I had them leave the muffs off . Kind of sounded half way between a glass pack and a turbo muff . I loved it back then but at 57 it would be too loud on that short of truck . Maybe ok on a C10 . I was using 2.5 inch pipe .
                            Previously HoosierL98GTA

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                            • #15

                              Re: Converters or Not?

                              " the days of pellet Cats is long gone and with them the 'restriction' that people rightly complained about"

                              I didn't know that but I'm guessing they still get hot enough to start a grass fire. That happened to a friend of mine on the deer lease years ago.
                              Cats need to be as close to the motor as possible, thus usually they're in the pipes coming down from the motor (which they are on my '40). Mufflers get every bit as hot as cats because the restriction builds heat... but the most important anti-fire device is the person who doesn't park in tall grass.... just sayin'

                              Thanks for all the input. I was leaning towards cats because of the smell. We notice that in the Camaro but not the Nova or Mustang which run on premium so maybe there is a difference there. My plan for the truck is to tune for 87 octane because I plan to use it as my daily in non snow season.

                              Does anyone have any specific converter recommendations? Motor is a 2003 5.3L and will have shorty headers with dual exhaust and a stepped up cam. Also keeping the factory fuel injection will dyno tune it once it is going.
                              I'm using these https://www.amazon.com/MagnaFlow-539...79411550&psc=1

                              they've survived a lot of abuse - which is important when you're tuning EFI

                              with that said, if you got the cats with the motor, use those - only 2 of them but you can mix and match, if you use the first position ones, you get manifold adapters as well and a leak-proof seal at the exhaust.....
                              Last edited by SuperBuickGuy; December 28th, 2019, 09:07 AM.
                              74NovaMan likes this.
                              Doing it all wrong since 1966

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