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  1. #1

    Default Putting Cats and Smog Back On

    So I have decided to put some of the pollution control back on my car to get rid of the stink and hopefully quiet it down a little.
    It is a carbureted 1980 with a swapped 302, no current smog equipment, vacuum valves or TAD/TAB solenoid valves. No computer to control them.
    A BBK catted H-Pipe is replacing the MAC off road H-Pipe and I am re-installing the smog pump. I do not need to pass any emissions testing, I just do not want my cats to plug up.

    For the thermactor air I planned to only run it to the pipe at the cats on the h-pipe.
    I was not going to add the pipe at the back of the heads as they are plugged, is it really required on a car only driven in the summer?
    I understand that I need a Thermactor bypass valve to block off the pump flow to he cats during deceleration or it will cause backfires.
    This thermactor valve needs to be actuated by a high vacuum level when the motor is being over run.

    This is where I am having issues.
    The thermactor bypass valve I bought runs opposite to this, it normally bypasses to atmosphere and under vacuum it supplies air to the cats.
    In the Haynes manual I have it talks of a bypass valve that functions like I need, but need to find its part number.
    I was wondering if one of these would be the right valve, but I can not find description on how they function.
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    Does anyone have a part number of an old school thermactor bypass that is actuated by high manifold vacuum? Or have the valve?


    Another solution is to use a vacuum differential valve that will dump the pilot signal to the atmosphere when there is a change in manifold vacuum - again I would need a part number.

    Will any of this actually work? Am I wrong with needing to turn the thermactor air off during decel?
    Again I am just trying to find a way to get air to my cats without causing other issues.
    Last edited by 0F0 CBR; 02-22-2021 at 03:14 PM.

  2. #2
    FEP Senior Member
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    Sprague River, OR
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    Default

    In curious where the air goes into the H-pipe. The OEM H-pipe air connection is downstream of the catalytic converters. It doesn't add air into the cats or before the cats. Does the BBK do that?
    Join The Conversation
    http://www.basinmotorsports.com

  3. #3

    Default

    The BBK air pipe enters the cats directly, in the middle.

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  4. #4

    Default

    I have those bbks and they are hooked to my down stream pump pipe. Upstream goes no where since I have 3-bar gt40 heads. I wonder if you couldn't get something off an old truck or something from that time frame or a little later even. They had carbs much later than cars did and might have used a simple engine vacuum design not requiring a computer. I bet an old 300ci straight 6 probably had the simplest design they could put together to pump air into the cat.

    Not sure if I am reading this right but it looks promising.Name:  300smogpump_42aa613b8a7e2aff444e715e8c3ab33ae197603f.gif
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    Apparently that is from a 1985 f150 with a 300 6

    I bet it still runs to a computer or temp controlled tad and not just manifold vacuum.
    Last edited by emerygt350; 02-23-2021 at 05:38 PM.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in stock dual snorkel
    GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers
    catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear.
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    Everything else stock and fully functional.

  5. #5

    Default

    I wonder if you really need to worry about off throttle back firing anyway. Is that 'really' a thing? If unburnt fuel is pouring into your cats when you decelerate I would have to think your car needs to be tuned. I mean, your oil would go before your cats too. If I were you I would just hook it up as always on and just see how it goes.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in stock dual snorkel
    GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers
    catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear.
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    Everything else stock and fully functional.

  6. #6
    FEP Senior Member Lubner's Avatar
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    Dec 2009
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    Levittown, NY
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    633

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    Just get a set of spun metallic cats no need for air pump. Modern cats work great.
    1981 Ghia Coupe
    Coyote/6R80

    1981 Cobra T Top
    306/C4

  7. #7

    Default

    You will get some backfire if you don’t have a check valve. You need a bypass valve attached to manifold vacuum plus the check valve. Look at previous post with the 300 ci six. After the check valve run to the BBK cats. Spun metallic cats work if you don’t want the smog pump.

  8. #8
    FEP Super Member xctasy's Avatar
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    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,785

    Default

    Quote Originally Posted by emerygt350 View Post
    I have those bbks and they are hooked to my down stream pump pipe. Upstream goes no where since I have 3-bar gt40 heads. I wonder if you couldn't get something off an old truck or something from that time frame or a little later even. They had carbs much later than cars did and might have used a simple engine vacuum design not requiring a computer. I bet an old 300ci straight 6 probably had the simplest design they could put together to pump air into the cat.

    Not sure if I am reading this right but it looks promising.Name:  300smogpump_42aa613b8a7e2aff444e715e8c3ab33ae197603f.gif
Views: 73
Size:  93.9 KB
    Apparently that is from a 1985 f150 with a 300 6

    I bet it still runs to a computer or temp controlled tad and not just manifold vacuum.

    Nice schematic. 1 bbl YFA Carter base engine. Most had the optional 2bbl Carter BDB.
    AMC 258 1 bbl above. Not the 250 Chev or 292 GMC.

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