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  1. #1
    FEP Member 0F0 CBR's Avatar
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    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
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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?
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  3. #3
    FEP Member 0F0 CBR's Avatar
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    Default

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

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  4. #4

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    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)
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  5. #5

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    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 a 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, dura grip (both Yukon)
    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)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  6. #6
    FEP Senior Member Lubner's Avatar
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    Just get a set of spun metallic cats no need for air pump. Modern cats work great.
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  7. #7

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    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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    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: 309
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.

  9. #9
    FEP Member 0F0 CBR's Avatar
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    So I started putting all of the smog and cats back on the car tonight, began with the smog pump so could get the right length belt measured.
    The Ford air pump I bought, label "E6VE-AA, 31 LB/HR", bolted to the bottom of the aluminum alternator bracket ok, but its pulley does not line up with the rest of the engine pulleys.
    Also the support bar that goes from the back of the smog pump to the engine block stud is misaligned by about 3/8"
    It is as if the whole pump should move towards the rad by about 3/8".
    Did they make different pumps for the different years? I think this is a newer pump off of a 93 maybe?
    Do older pumps have a different offset?
    I have a old non roller 302 engine with 1985 accessory drives and brackets.

  10. #10
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    I think the pumps are similar and it’s the pulley that makes the offset. Some years had separate belt like 74 2.8l.
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  11. #11
    FEP Member 0F0 CBR's Avatar
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    So I ended up getting a alternator bracket from an 85 and that fixed my belt alignment issues. The 79 bracket I had offsets the smog pump by 1/4".
    Anyway I have completed the re-installation of the air pump, diverter valve and full headers back exhaust system.
    It was quite a kit when all layed out.

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    After installing the system I realized the BBL h-pipe was about 1 1/2" inches shorter than my 30 year old MAC one. It would not reach the connection to my axle back exhaust. So I cut off the old mufflers and tail pipes and bought new ones. Needed an excuse to replace it anyway.
    I went with the Magnaflow mufflers and Flowmaster tailpipes.
    Painted all of the aluminized parts with high heat paint before installing.
    Had fitment issues around the rear brake hose, so also moved it to the center.
    The brake lines from a 8.8 fit ok on my 7.5, the hose I sourced fit was for a 85 with 7.5, and I bought the repo banjo bracket from LMR.

    The cats make a big difference on the smell, no more stinky clothes and wife even likes it now.
    The Magnaflows are not a quiet as I had hoped and still get an annoying drone in the 2400-2700 rpm range.
    Above and below this range it is good.
    The performance increase can really be felt in the upper RPMs, pulls nice now with no flattening out on the top end.
    Wish I did it years ago.

  12. #12

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    What do you attribute the performance increases to?

  13. #13
    FEP Member 0F0 CBR's Avatar
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    Knew I was going to get asked that.
    The old axle back was 2 1/4" non-mandrel bent pipes. Mufflers were probably restrictive too.
    I figure this is what made the difference.
    Last edited by 0F0 CBR; 07-02-2021 at 05:40 PM.

  14. #14

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    I definitely know that smell, I guess it's an acquired taste of sorts. Not something I would want on my DD, but it reminds me of the track. My WRX was catted and that was for performance as the turbo sat right in front of it and I wanted a certain amount of back pressure. On my 99 GT, I had cats, simply because I thought with the X pipe I had and Magnaflows, they sounded better. Now, it's near impossible to buy O/R versions of H-pipes off of sites like LMR or AM. I can see these environmental acts already having a major affect on the performance parts we choose. Glad to hear you got your car fixed tho! With all that work, I know I would have just stopped after putting cats on it.
    1986 Mustang GT -DGM- Trick Flow 360 HP Top End Kit. TF 170CC Heads, TF Track Max Cam, TF TM Intake
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