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Air pump question

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gregsdrums

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Had a valve job done on my 72 1275 and after putting it back together removed the air pump and smog stuff. The engine is stock and was wondering if any one else has done this and what difference it made to the way the engine runs.
 
The air pump does very little harm to engine performance, is very reliable, and is pretty effective at reducing exhaust pollutants. Many manufacturers went the cheap route to smog control, but the more expensive air pump system maintained performance better than many of the cheap fixes that came about in the early 70s. For that reason, I leave the system installed on my '71 BGT, since I live in an urban area where air pollution is an issue. If you live in a rural area with few cars then removing the system would seem justified (though not legal) and would declutter the engine compartment. However, you won't notice any performance difference. It wasn't until later (i.e. 1975 on) that the smog equipment started to substantially degrade performance.
 
The degree of exhaust dilution due to air injection is relatively minor and is irrelevant to pollutant reduction. The air is injected at the exhaust port so that incompletely combusted exhaust gases (due to overly rich mixtures and insufficient time for complete combustion) can continue to burn while exiting through the exhaust plumbing. The temperature of the exhaust gases drops rapidly downstream of the exhaust plumbing so injecting air downstream won't sustain any combustion reactions.

For later cars with catalytic converters the air pump is even more critical because it helps reduce the "poisoning" of the catalyst by unburned fuel.
 
davester said:
...(due to overly rich mixtures and insufficient time for complete combustion)...
Click to expand...
Both of which could be rectified by properly setting your carb and timing, right? So...the air pump was a workaround fix for people who don't do tuneups?
 
bthompson said:
davester said:
...(due to overly rich mixtures and insufficient time for complete combustion)...
Click to expand...
Both of which could be rectified by properly setting your carb and timing, right? So...the air pump was a workaround fix for people who don't do tuneups?
Click to expand...

No. That's not true at all. When I said "overly rich", I meant in relationship to a stoichiometrically perfect mixture for complete combustion. No way is that going to happen very often using a crude device like a carburetor to adjust the mixtures on the fly. Even with near perfect mixtures provided by electronic fuel injection, there are still areas of the combustion chamber where incomplete combustion occurs, and during warm up of any kind of engine there is always lots of unburnt fuel going out the exhaust port. Also, the time available for combustion of the mixture varies with engine speed...there may be insufficient time at the P and T necessary for combustion before the mixture is ejected via the exhaust valve.

The air pump is not a "workaround". It is a very efficient way to "polish" the inevitable unburned hydrocarbons as they exit the exhaust valve. That's why almost all of the manufacturers used them. Do you remember how nasty it used to be sitting in traffic breathing exhaust fumes in the 60s? I do! The early smog systems, consisting mostly of air pumps and a bit of mixture leaning and timing advance shenanigans took that situation from absolutely awful to not half bad.
 
I won't enter the great air pump debate, but will say this, anything the engine has to drive draws some HP, that why most of the SCCA and vintage MG racers don't run any charging systems, meaning no alternator, just run off battery charge, because we're only running for short period, like 30-45 minutes and there really good battery that can run much longer than this at full charge. They broke alot is what I remember about them, on MGs and all other cars for that matter, I ran a Goodyear auto repair center for years, and we replaced alot of them, especially on GM cars.
 
Hap Waldrop said:
I won't enter the great air pump debate, but will say this, anything the engine has to drive draws some HP
Click to expand...

Absolutely. I'm just saying that air pump drag is negligible and won't be noticeable, especially on a street car. Ever tried spinning an MG air pump by hand?...very little drag.

I didn't know this was a debate....I was just trying to clear up some misconceptions.
 
Now you guys made me feel bad for starting this "debate". With all the technical lingo being thrown around, I think I'm going to put my "dunce cap" on and go sit in the corner...
 
Hey, I learned something from this exchange - I'm glad you started it.
 
I've had the bearing seize and leave me looking for a new fan belt - and things like that can't possibly ever be good.
Now I would never run an LBC with one hooked up.
If it's on there and you need it for "originality" fine, but you don't have to hook it up.
 
Well, from what we learned in smog classes in California, in the early 70's...prime purpose of the air pump was to cut down the oxides of nitrogen... Anything that helped cool off(from the instructors description) the exhaust gasses while still upstream would reduce the oxides of nitrogen at the tailpipe... We tried this on a couple of dynos at school. Had a wild hair so I used a water injection pump off of my old man's Ak Miller turboed pinto.. And it worked. cut down the measured oxides of nitrogen greater than the air pump.. Only difficulty is that people would not refill the water reservoir.. So that's why the manufacturers went to air pumps.. Before they discovered egr did essentially the same thing, but it also cost more horsepower as you were diluting the fuel/air mixture before combustion..
 
Ron, I think you're thinking of the EGR system, which puts noncombustible exhaust gases into the combustion chamber for the express purpose of reducing the temperature of combustion so that nitrogen oxides (NOx) don't form (and you're right, high combustion temperatures produce NOx). I believe the air pump is primarily aimed at reducing hydrocarbons and carbon monoxide by continuing their combustion, though the cooling effect of the fresh air probably does help lower NOx created during that combustion.

Edit: Oops, didn't notice the last sentence in your post.

It's interesting to hear stories about air pumps failing. I've owned a lot of cars with air pumps, many of them LBCs, with nary a failure so have assumed that they are pretty reliable beasts. No doubt they do wear out eventually but I wonder how frequently they do actually fail. Any pro mechanics have info on this? I can see how your experience could make you shy away from them RickB, but given the very real and observable improvements in air quality these things make, with almost no performance hit (not to mention wanting to keep my cars fairly original), I'd recommend keeping them operational.
 
davester said:
I wonder how frequently they do actually fail. Any pro mechanics have info on this?
Click to expand...

How would you know? I'm not being silly here, if the pump pulley keeps turning, It would take an exhaust gas analyzer to know wouldn't it?
 
...or you can put your palm over the pump intake to see if it is still sucking.
 
Every one that I have had to remove/replace due to failure has been due to bearing failure/seizing, usually seizing. Occasionally I have seen the rotor blades wear so small that they fell out and jammed but that has only been once (twice?).
They are pretty simple beasts and the bearings can be replaced but I have never found (nor looked for) rotor blades.
By the way- in about 40 years of playing with these cars I have only seen maybe 8 pump failures.
Bill
 
Dave you are right, and I am too, somewhat.. The INITIAl purpose of air pumps was to cut down on hydrocarbons. Nada could be done with Co without a cat. Then the manufacturers learned that by placing the point of air injection just downstream of the exhaust valve the nox would be reduced... along with hydrocarbon reduction.So that is when the air pump became ubiquitous. Until the cheaper egr came around..
 
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