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  1. #1

    Question Placement of Catalytic Converters

    Did a quick search on this, but didn't see anything right off that answered my question.

    I posted in my build thread that I picked up a pair of Magnaflow universal catalytic converters (#59956) after seeing several recommendations here on the forum with hopes of cleaning up some of the exhaust smell of my car and make it a bit more pleasant to drive. Running an offroad H-pipe currently.

    Is there a certain distance from the exhaust port that they should be installed? Is it better to get them closer to the engine or further away? Or is it not that critical? These are small enough that they can be installed about anywhere in the horizontal portion of the mid-pipe. One member here posted photos of a pair of the same converters installed just ahead of the crossover on their mid-pipe. Is this a preferred location?

    This is my first time dealing with catalytic converters.

    Appreciate the help.
    Thomas

    1985 Mustang GT - Build Thread
    347 (Stock Block, Scat Crank & Rods, Probe Pistons, 11:1 CR, AFR 185's, PP Crosswind Intake, Custom-ground Comp Hyd Roller Cam, Scorpion 1.6 Roller Rockers, Holley 3310-4), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, Strut Tower Brace, K-Member Brace, Bilstein HD Struts/Shocks, MM/H&R Springs, SN95 5-Lug, Cobra Brakes, '04 Mach 1 Steering Rack

  2. #2

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    As close to the engine as possible. This will bring them up to temperature more quickly and increase their efficiency.
    Jim DeAngelis
    Cornucopia of Useless Knowledge
    Connoisseur of Dearborn Ferrous Oxide
    '83 GT hatch, currently under the knife
    '79 Capri 2.3L n/a, Medium Copper metallic, survivor
    (bought from MRausch82)

  3. #3

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    Quote Originally Posted by FB71 View Post
    As close to the engine as possible. This will bring them up to temperature more quickly and increase their efficiency.
    I believe this is an accurate statement. BUT, I don't believe the position has anything in the world to do with reducing the fumes or smell you are trying to get rid of. If the car is not tuned correctly and you are trying to band-aid that with converters, I suspect you will be replacing the converters every year. They aren't supposed to be a band-aid for poor tuning. I am not saying you car is not tuned right, how would I know, just throwing it out there.
    Liberty once lost is lost forever.

    John Adams
    July 7, 1775

  4. #4

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    I skipped over you mentioning the addition of "cats" in your other thread, because, truthfully, where I'll be placing mine when they come off is into the trash. They serve no purpose in a correctly running (your super-tuning of AFR should be producing nothing but the sweet smell of efficient and complete combustion) engine running more correctly. I don't know for absolute certain, but I don't think cats will do much but take up space on your combination without the existence of an air pump, feeding cats the air they require to burn up unburnt fuel with an (far from truly efficient) EFI combination...
    Last edited by Walking-Tall; 07-07-2017 at 06:22 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  5. #5

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    I don't know the optimum placement, but getting it too hot can kill a catalytic converter. This usually happens due to excessively rich mixture. I killed one in a miata when the coil went bad and two of the four cylinders stopped firing. Here is a good overview that I found: http://www.aa1car.com/library/converter.htm

  6. #6

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    maybe apple to orange comparison but took cat off my 96 F250 w/460. what I noticed was tail pipe went from clean to sooty, the exhaust gas coming out of tail pipe is noticeably cooler , smell of exhaust gas is much smellier, decrease in mpg, and no noticeable increase in power or torque. just my 2 cents for what its worth

  7. #7

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    Quote Originally Posted by palm city mike View Post
    maybe apple to orange comparison but took cat off my 96 F250 w/460. what I noticed was tail pipe went from clean to sooty, the exhaust gas coming out of tail pipe is noticeably cooler , smell of exhaust gas is much smellier, decrease in mpg, and no noticeable increase in power or torque. just my 2 cents for what its worth
    Exactly. Tail pipes with soot in them and a fuel-swilling smelling exhaust isn't an indication of a catalytic converter deficiency in an exhaust system, but of an engine not running as efficiently as it could/should be. Complete and efficient internal combustion produces very little HC (hydrocarbons, unburnt fuel) or CO (carbon monoxide, another byproduct of air/fuel not completely being burned/utilized)... the two excessive byproducts found with efi systems that the cats are to burn up. Call me old-school crazy, but I'm stuck with the inclination that air and fuel is much better burned and used to propel a vehicle inside the engine's combustion chambers as opposed to with add-on air-fed catalytic converters downstream in the exhaust system.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  8. #8

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    Thanks all.

    I agree, they are not a bandaid for poor tuning. That is something I've been working on over the last several years and made great progress with over the last few months. Mike, you know where I'm at with this. Results have been documented in my carb tuning / drivability thread. I may not be at the optimum tune for my combination, but it's definitely not overly rich either. However, I have yet to find a carb setting that eliminates the exhaust smell, at least at idle. Not sure if that ideal idle mixture window is so small I have yet to hit it or if there is something about my combo that just won't allow it.

    The exhaust smell is significantly better than it used to be. I've been fighting this for a long time. Like I said, tired of smelling like exhaust after driving the car, being limited to when and where I drive and the necessary post-drive shower.
    Last edited by 85MUSTANGTGT; 07-07-2017 at 09:52 PM.
    Thomas

    1985 Mustang GT - Build Thread
    347 (Stock Block, Scat Crank & Rods, Probe Pistons, 11:1 CR, AFR 185's, PP Crosswind Intake, Custom-ground Comp Hyd Roller Cam, Scorpion 1.6 Roller Rockers, Holley 3310-4), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, Strut Tower Brace, K-Member Brace, Bilstein HD Struts/Shocks, MM/H&R Springs, SN95 5-Lug, Cobra Brakes, '04 Mach 1 Steering Rack

  9. #9

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    Yep. It might idle happily and fine with the idle mixture screws wound in a tad more. There's no set AFR # for that, or any load/rpm for that matter (as you know, everything is combination specific and to what the engine likes, which doesn't always agree with what a WB says or what purported best WB readings should be for differing scenarios), besides a fairly universal and safe ~12.5:1 for WOT duty, but shooting for or approaching "stoich" 14.7:1 at idle can be a good thing, but again, it's smoothness and/or manifold vacuum will tell you what's lean-best. Idle usually does require a slightly richer AFR than off-idle and easy-to-moderate transition/cruise.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  10. #10

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    Well, not sure what to do then.

    I feel my car is running reasonably well. AFR's are in what I would consider an acceptable range. I do still plan to do work more on tuning.

    Much of my research seemed to indicate that the SBF is just inherently fumy and that many had installed cats and had success in eliminating or at least reducing their exhaust smell. Thought that I might get the same experience.
    Thomas

    1985 Mustang GT - Build Thread
    347 (Stock Block, Scat Crank & Rods, Probe Pistons, 11:1 CR, AFR 185's, PP Crosswind Intake, Custom-ground Comp Hyd Roller Cam, Scorpion 1.6 Roller Rockers, Holley 3310-4), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, Strut Tower Brace, K-Member Brace, Bilstein HD Struts/Shocks, MM/H&R Springs, SN95 5-Lug, Cobra Brakes, '04 Mach 1 Steering Rack

  11. #11

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    A good while ago one of the auto magazines did a big block 60's Firebird for dragstrip duty, and to meet certain "emissions" compliance. They used large diameter cats and added air tubes ahead of them with one way air pump check valves, that allowed air for the cats to be passively drawn in by exhaust flow, for the cats to do their scrubbing. Maybe that'd be something to try... or adding an air pump... ?
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  12. #12

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    The threads I read of those who were using this particular converter stated they would survive without the air injection.

    Here's a few of the threads that were my motivation for wanting to give this a shot.

    http://vb.foureyedpride.com/showthre...placement-cats

    http://vb.foureyedpride.com/showthre...ax-VT-mufflers

    http://vb.foureyedpride.com/showthre...-no-more-stink

    There are several others also. Some of these cars are fuel injected, but I don't see that to be relevant.
    Thomas

    1985 Mustang GT - Build Thread
    347 (Stock Block, Scat Crank & Rods, Probe Pistons, 11:1 CR, AFR 185's, PP Crosswind Intake, Custom-ground Comp Hyd Roller Cam, Scorpion 1.6 Roller Rockers, Holley 3310-4), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, Strut Tower Brace, K-Member Brace, Bilstein HD Struts/Shocks, MM/H&R Springs, SN95 5-Lug, Cobra Brakes, '04 Mach 1 Steering Rack

  13. #13

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    I recently asked LMR about the Flowmaster cats they offer, and they said they do not require air injection.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  14. #14
    FEP Super Member webestang's Avatar
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    Quote Originally Posted by 85MUSTANGTGT View Post
    The threads I read of those who were using this particular converter stated they would survive without the air injection.

    Here's a few of the threads that were my motivation for wanting to give this a shot.

    http://vb.foureyedpride.com/showthre...placement-cats

    http://vb.foureyedpride.com/showthre...ax-VT-mufflers

    http://vb.foureyedpride.com/showthre...-no-more-stink

    There are several others also. Some of these cars are fuel injected, but I don't see that to be relevant.

    In that first thread I mentioned I have a cat and no other snog stuff on my 2.3. After 2 years my universal Walker cat is doing just fine.

    Scotty
    1985 Fox Notch 4-banger Ranger tube header Eastwood Royal Blue
    1988 Fox LX 5.0 AOD Vert BBK 170mph speedo Candy Apple Red
    1999 Mustang Coupe V6 Auto Chrome Yellow -Daily Driver.
    Past Pony's.....
    68 Coupe Inline-6 3-Speed-Man. Primer
    78 II Hatch 302 3-Speed-Auto Sunroof Black
    81 4-Eye Coupe 4-Banger 4-Speed-Man. White

  15. #15

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    Brad & Scotty,

    Thanks for sharing your findings.
    Thomas

    1985 Mustang GT - Build Thread
    347 (Stock Block, Scat Crank & Rods, Probe Pistons, 11:1 CR, AFR 185's, PP Crosswind Intake, Custom-ground Comp Hyd Roller Cam, Scorpion 1.6 Roller Rockers, Holley 3310-4), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, Strut Tower Brace, K-Member Brace, Bilstein HD Struts/Shocks, MM/H&R Springs, SN95 5-Lug, Cobra Brakes, '04 Mach 1 Steering Rack

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