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That is how car manufacturers worked around the old tail pipe emission laws. They added air pumps plumbed to the exhaust manifold(s) to increase the exhaust mas

That is how car manufacturers worked around the old tail pipe emission laws. They added air pumps plumbed to the exhaust manifold(s) to increase the exhaust mass diluting the stream enough to pass emissions tests. Problem solved!

SoftTalker 5mo ago
Is that what a "smog pump" is (was)? LOL. I had heard the term but never knew what it was. Along the same lines then as other emissions equipment that reduced fuel economy but achieved the ppm criteria in the exhaust. Yes, let's address pollution by burning more fuel.
- CamperBob2 5mo ago
  Yes, and it has absolutely nothing to do with increasing air volume. The idea is to lower hydrocarbon emissions by burning them off in the exhaust manifold.
  - MisterTea 5mo ago
    Depends on the vehicle. Again, I was in a medium duty truck where this system was used.
    - CamperBob2 5mo ago
      No, it does not "depend on the vehicle." Stop spreading bullshit. Failing that, do it elsewhere.
cucumber3732842 5mo ago
>That is how car manufacturers worked around the old tail pipe emission laws. They added air pumps plumbed to the exhaust manifold(s) to increase the exhaust mass diluting the stream enough to pass emissions tests. Problem solved! I'm sure that people of a certain bent will eat your comment up but that's just not true. Air pumps were for catalyst efficiency. The old ones needed extra oxygen molecules floating around for the big stuff (hydrocarbons) to oxidize with until the catalyst was up to operating temp and working at peak-ish efficiency. Emissions have been measured by mass rather than concentration since 1972. So like yeah it "could've been done" but standards before that were light enough that they could just screw with other things that add $0 to the BOM to clean it up enough to pass.
- MisterTea 5mo ago
  > Air pumps were for catalyst efficiency. The old ones needed extra oxygen molecules floating around for the big stuff (hydrocarbons) to oxidize with until the catalyst was up to operating temp and working at peak-ish efficiency. My experience comes from driving and working on a 1988 GMC 6000 truck with an anemic 350 small block with a Muncie SM465 behind it. There was no catalytic converter, only a muffler. It featured not one, but two air pumps, each feeding a set of pipes that led to metal tubes which entered the exhaust manifold opposite each exhaust port. Another odd thing about that truck was it had a choke lever, something I thought was long gone by 1988, and was a pain to start in the winter. Perhaps other vehicles had a cat but this truck certainly did not.
  - cucumber3732842 5mo ago
    350ish (or less) + 4spd trucks kinda fell out of favor over the course of the 70s for bigger engines and 5spds (usually with a 2spd rear end but I digress). I'm sure you could still get one, but who would when you could get something better on the lot for the same money. Sounds like someone swapped a 70s-80s engine from a lighter application in. I don't think that truck would've had manual choke from the factory. Lots of stuff could've happened over the years. The amount of air your engine breathes is monumental compared to what the smog pump moves. The math of dilution just doesn't work. What does work is pissing a light stream of oxygen (remember, not much of that coming out of the engine, especially on warm up while it runs rich) to help the catalyst burn those hydrocarbons off of itself a wee bit faster. I'm not sure if an 80s gas MDT would've had cats from the factory.
    - alistairSH 5mo ago
      The 6000 was a commercial truck. It appears to have had a carburetor for most if not all of the 1980s.
      - MisterTea 5mo ago
        Totally had a carb since it had a choke lever.
Aurornis 5mo ago
This is completely false. The ECU turns on the secondary air system and enriches the fuel mixture so the exhaust temperature goes up, heating the catalytic converter rapidly. Catalytic converters must be hot to work, so getting them hot quickly is important. https://en.wikipedia.org/wiki/Secondary_air_injection https://en.wikipedia.org/wiki/Secondary_air_injection EDIT: OP drove an older truck. In earlier days, the extra air injection into the exhaust was to provide some air for the secondary exhaust gasses to fully burn. It had to be done early in the exhaust where the exhaust gases are hot.

SoftTalker 5mo ago

Is that what a "smog pump" is (was)? LOL. I had heard the term but never knew what it was. Along the same lines then as other emissions equipment that reduced fuel economy but achieved the ppm criteria in the exhaust. Yes, let's address pollution by burning more fuel.

CamperBob2 5mo ago
Yes, and it has absolutely nothing to do with increasing air volume. The idea is to lower hydrocarbon emissions by burning them off in the exhaust manifold.
- MisterTea 5mo ago
  Depends on the vehicle. Again, I was in a medium duty truck where this system was used.
  - CamperBob2 5mo ago
    No, it does not "depend on the vehicle." Stop spreading bullshit. Failing that, do it elsewhere.

cucumber3732842 5mo ago

>That is how car manufacturers worked around the old tail pipe emission laws. They added air pumps plumbed to the exhaust manifold(s) to increase the exhaust mass diluting the stream enough to pass emissions tests. Problem solved! I'm sure that people of a certain bent will eat your comment up but that's just not true. Air pumps were for catalyst efficiency. The old ones needed extra oxygen molecules floating around for the big stuff (hydrocarbons) to oxidize with until the catalyst was up to operating temp and working at peak-ish efficiency. Emissions have been measured by mass rather than concentration since 1972. So like yeah it "could've been done" but standards before that were light enough that they could just screw with other things that add $0 to the BOM to clean it up enough to pass.

MisterTea 5mo ago
> Air pumps were for catalyst efficiency. The old ones needed extra oxygen molecules floating around for the big stuff (hydrocarbons) to oxidize with until the catalyst was up to operating temp and working at peak-ish efficiency. My experience comes from driving and working on a 1988 GMC 6000 truck with an anemic 350 small block with a Muncie SM465 behind it. There was no catalytic converter, only a muffler. It featured not one, but two air pumps, each feeding a set of pipes that led to metal tubes which entered the exhaust manifold opposite each exhaust port. Another odd thing about that truck was it had a choke lever, something I thought was long gone by 1988, and was a pain to start in the winter. Perhaps other vehicles had a cat but this truck certainly did not.
- cucumber3732842 5mo ago
  350ish (or less) + 4spd trucks kinda fell out of favor over the course of the 70s for bigger engines and 5spds (usually with a 2spd rear end but I digress). I'm sure you could still get one, but who would when you could get something better on the lot for the same money. Sounds like someone swapped a 70s-80s engine from a lighter application in. I don't think that truck would've had manual choke from the factory. Lots of stuff could've happened over the years. The amount of air your engine breathes is monumental compared to what the smog pump moves. The math of dilution just doesn't work. What does work is pissing a light stream of oxygen (remember, not much of that coming out of the engine, especially on warm up while it runs rich) to help the catalyst burn those hydrocarbons off of itself a wee bit faster. I'm not sure if an 80s gas MDT would've had cats from the factory.
  - alistairSH 5mo ago
    The 6000 was a commercial truck. It appears to have had a carburetor for most if not all of the 1980s.
    - MisterTea 5mo ago
      Totally had a carb since it had a choke lever.

Aurornis 5mo ago

This is completely false. The ECU turns on the secondary air system and enriches the fuel mixture so the exhaust temperature goes up, heating the catalytic converter rapidly. Catalytic converters must be hot to work, so getting them hot quickly is important. https://en.wikipedia.org/wiki/Secondary_air_injection https://en.wikipedia.org/wiki/Secondary_air_injection EDIT: OP drove an older truck. In earlier days, the extra air injection into the exhaust was to provide some air for the secondary exhaust gasses to fully burn. It had to be done early in the exhaust where the exhaust gases are hot.