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    1. #1
      Join Date
      Mar 2007
      Location
      Mission Viejo, CA
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      610
      Country Flag: United States

      Catalytic converters on older musclecars

      I am looking for anyone that has installed catalytic converters on thier older non emission performance car and what type of results they have seen. I am considering installing dual cats on my 466 inch EFI Pontiac to help reduce emissions and clean up the exhaust. The car is making over 550 HP. Thanks.



    2. #2
      Join Date
      Jan 2000
      Location
      Thousand Oaks California
      Posts
      9,792
      Country Flag: United States
      I have kicked around this idea myself for years. It will be interesting to see if anyone else has done it.
      Larry Callahan
      Founder/Administrator of Pro-Touring.com, G-Machines.com and HostMyJunk.com
      To advertise on Pro-Touring.com click here

    3. #3
      Join Date
      Mar 2005
      Location
      Linwood,NC
      Posts
      99
      I have a set of 3" high flow thunderbolts on my camaro. I have a LS2 in the car. I basically put them on to get rid of the gas fume smell. They work great. Smoothed out the exhaust rasp and quieted it down a bit. I didn't notice any HP lose.

    4. #4
      Join Date
      Mar 2007
      Location
      Mission Viejo, CA
      Posts
      610
      Country Flag: United States
      That was my main reason why I wanted to do it in regards to the exhaust smell. What brand of cats did you use. Did it quiet the car down as well?

    5. #5
      Join Date
      Aug 2005
      Location
      Hamilton, NJ
      Posts
      4,253
      Country Flag: United States
      I had to take the cats (typical 2 in a dual setup, not OE) out of my 77 because of clearance issues when I put the t56 in. the difference in odor is noticeable. I did not notice a significant sound difference that I remember.

      I have thought about adding high flow bullet cats right after the collector, if the project $$ is there. One of the rags, maybe GMHT, did an article showing the HP loss from open Y to aftermarket hi flows on an LS2 GTO. Loss of HP was <10. I'm not running for all out hp, I use unleaded street gas, I like clean air, I don't see why not. Maybe flange them on both side to take them out if I want. The cat in my 82 TA was flanged and I would swap it in for inspection. I was a scofflaw teen.
      Scott from NJ.

      Vent Windows Forever! ... My junk, featuring the Red Dragon ... NastyZ28 ... NJ Camaros & Firebirds

      Feather-light suspension, Konis just couldn't hold
      I'm so glad I took a look inside your showroom doors

    6. #6
      Join Date
      Mar 2007
      Location
      Mission Viejo, CA
      Posts
      610
      Country Flag: United States
      I've owned performance cars for a long time, but I am starting to get tired of the smell and just want to be able to clean up the exhaust without sacrificing too much power. A loss of less than 10 hp is not going to be noticeable in a 500+ hp street car. But will cats be subject to failure if you are running a larger cam with a lot of overlap? I have the ability to tune due to the EFI, so I would think I would be safer than if I was running a carb.

    7. #7
      Join Date
      Aug 2004
      Location
      San Antonio, Tx
      Posts
      1,180
      just remember they need to be as close to the engine as you can or it will take them longer to heat up. that is the reason for A.I.R. pumps on GM, to help light off the cats quicker.
      Instagram: CamaroAJ

    8. #8
      Join Date
      Oct 2004
      Location
      Pittsburgh, PA
      Posts
      1,234
      Country Flag: United States
      Quote Originally Posted by CamaroAJ View Post
      just remember they need to be as close to the engine as you can or it will take them longer to heat up. that is the reason for A.I.R. pumps on GM, to help light off the cats quicker.

      I will be running Random Technology bullet cats on mine when all is said and done. Odor is the main driver. Going to put V-band adapters on the inlet and bolt them right up behind the headers.
      Nick DiPrenda

    9. #9
      Join Date
      Mar 2007
      Location
      Mission Viejo, CA
      Posts
      610
      Country Flag: United States
      CamaroAJ: I agree on the positioning. I will mount them as close to the collector as I can to light them off faster. Spoke with Magnaflow today about cats and what they recommend. Apparently California residents can not buy certain types of converters. They are illegal for installation. I will work around that though.

    10. #10
      Join Date
      Jun 2001
      Location
      Los Angeles
      Posts
      5,721
      Country Flag: United States
      Many of the Magnuson "shop" cars have them. Chassis dyno tuning has typically shown a 5-10hp loss on a 500-600hp engine.

      I'm looking into fitting them as well. It's really nice to have nearly zero smell.
      VaporWorx. We Give You Gas http://www.vaporworx.com

    11. #11
      Join Date
      Dec 2009
      Location
      San Diego, CA
      Posts
      228
      Country Flag: United States
      Quote Originally Posted by Later-A-body View Post
      CamaroAJ: I agree on the positioning. I will mount them as close to the collector as I can to light them off faster. Spoke with Magnaflow today about cats and what they recommend. Apparently California residents can not buy certain types of converters. They are illegal for installation. I will work around that though.
      I just bought the metal spun cats manufactured by magnaflow on ebay. http://cgi.ebay.com/ebaymotors/ws/eB...=STRK:MEWNX:IT

      I believe what magnflow stated is true because Summit/Jegs will not sell the cats I purchased on ebay to california anymore. I bought the cats for the same reason everyone else seems to have them for, smell.

    12. #12
      Join Date
      May 2002
      Location
      Northern California
      Posts
      10,773
      Country Flag: Bosnia Herzegovina
      You guys running cats, are you experiencing any over heating exhaust issues since I assume most of these fuel systems are not even close to stoichio?

      we ran a cat on a race 3rd gen Camaro with carbed 383/big roller cam and it was cherry red half the time.
      vince
      MrQuick ΜΟΛ'ΩΝ ΛΑΒ'Ε

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    13. #13
      Join Date
      Feb 2008
      Location
      Sesser, Il
      Posts
      490
      And people thought I was NUTZ for putting dual cats under my Cutlass instead of leaving them out...

      I was running dual cats on the pass side where the stock single cat was. I'm thinking this time around I'll just run a regular duals straight back with a cat on each side.

      What is everyone doing about heat shielding on the cars that didn't have stock cats? I know some cats have a heat shield, is that ehough heat shielding or are you running a heat shield on the floor pan?
      Doug Gulley

      66 C10 383, AFR 190, Accel SuperRam, Hyd Roller 230*/236* 280XFI, aftermarket T56, *under construction*

    14. #14
      Join Date
      Oct 2004
      Location
      Pittsburgh, PA
      Posts
      1,234
      Country Flag: United States
      Quote Originally Posted by MrQuick View Post
      You guys running cats, are you experiencing any over heating exhaust issues since I assume most of these fuel systems are not even close to stoichio?

      we ran a cat on a race 3rd gen Camaro with carbed 383/big roller cam and it was cherry red half the time.
      vince
      How rich were you guys running? I could definitely see boosted cars having issue. N/A cars should be around the 12.5-13.0/1 range for A/F. As long as there are no misfiring issues, I would think a cat would have no issue behind that.
      Nick DiPrenda

    15. #15
      Join Date
      Mar 2007
      Location
      Mission Viejo, CA
      Posts
      610
      Country Flag: United States
      Good point on the heat shields. The Magnaflow spun cats dont have them. I have my AFR tuned to run at 14.4 at cruising speed, and progressively adjusts as low as 12.5 under WOT.

    16. #16
      Join Date
      Aug 2004
      Posts
      23
      You can use either a two way or three way cat with a carb, but you really have to keep a close tab on the a/f ratio. If your running too rich ( which is often the case with large overlap cams) you run the risk of overheating the converter and destroying it's effectiveness. At worst, you can have the substrate completely destroyed, wich could clog the converter. Too lean will drastically reduce it's effectiveness.

      Using cats with efi is really straight forward and I see no reason why they shouldn't be added, especially if you're running closed loop under most driving conditions. Modern aftermarket high flow cats don't pose much, if any, of an exhaust restriction, unlike the old OEM pellet style converters of the late seventies and early eighties.

      John

    17. #17
      Join Date
      Feb 2007
      Location
      USA, TN
      Posts
      851
      Why not weld a header flange on it and bolt it straight to the header?

    18. #18
      Join Date
      Feb 2009
      Location
      muggy midwest
      Posts
      534
      Country Flag: United States
      Why not run a methanol injection? That will solve your odor issue and add a bit more power as well as keep carbon deposits in check. Also, running it will raise your octane rating slightly as well.
      "...if at first you don't succeed, try again.
      If you still don't succeed, then quit-no sense being a damn fool about it..."
      -W.C. Fields

      HARNESSWORX
      (formerly gmachinz)

    19. #19
      Join Date
      Mar 2005
      Location
      Loganville, GA
      Posts
      937
      Country Flag: United States
      Since I just recently finished an LT1 swap in my 67 Elky, I am surprised at how clean the exhaust is on the car without cats, compared to the carbed 377 that was there before. I was expecting to have more exhaust odor. EFI has it benefits. The 377 would have killed any cats I put on it in short order. It would make your eyes water and run you out of the garage even with all the doors open. Of course it didn't have anything to do with the crossram and 2 holleys on top, no sir nothing at all.
      2018 Cruze LT Hatchback
      2003 Suburban 2500 8.1L
      1975 MGB Roadster
      2003 GSX750F Katana

    20. #20
      Join Date
      Aug 2004
      Location
      Rustburg, Virginia
      Posts
      3,695
      Country Flag: United States
      I'm thinking about adding cats too.....we'll see.
      1970 RS/SS350 139K on the clock:
      89 TPI motor w/ 1pc rear seal coupled to a Viper T56 via Mcleod's modular bellhousing w/ hydraulic T/O bearing from the Viper, 12 bolt rear w/ 3.73 gearing, SC&C upper control arms, factory lowers with Delalums, C5 brakes at all four corners, Front Wheels 17x8's with Sumi 255/40/17 and Rear Wheels 17x9's with Sumi 275/40/17.
      Brief description of the work done so far can be found here: http://www.nastyz28.com/forum/showthread.php?t=112454


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