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MG Midget and Sprite Technical - Air pump question

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.
GF Greg Smith

Greg. In theory, the air pump was used to pump fresh air into the exhaust gasses which allowed them to continue burning while making their way through the exhaust system. However, it is the belief of a number of us that what actually happens is that the fresh air injected into the burned gasses dilutes the exhaust gasses, at the tail pipe where emissions readings are taken, without truly making any effective difference in the actual pollution being produced. Professional mechanics point out that the air pump is not an emissions control feature on modern cars and has not been for a number of years.

The air pump does require that some of the power being produced by the engine be used to turn the air pump which compresses ambient air and injects it into either the cylinder head or exhaust manifold. Thus, the air pump "robs power from the engine". Not a lot, but these engines, in factory form, did not produce the vast amounts of horsepower that the US engines of the same period did.

Hence, many people decide to remove the air pump and the associated parts from their vehicles and to plug the various holes associated with the injection system. It does not require any retuning of the engine when this is done, it reduces the amount of clutter under the hood, and it removes one more rotating part which, from time to time, goes bad and has to be replaced.

I have little use for the air pump. The charcoal canister(s) and the evaporative loss containment system, however, is an excellent idea, works well, and should be kept in good working condition.

If you do decide to leave the air pump off, keep the parts. Some places require emissions inspections and some emissions inspections require that you have all of the original pollution control equipment installed on your engine. Hence, keeping the original parts available is a good idea, even if they are not installed on the engine.

Les
Les Bengtson

I removed the air pump when I first got my 72
because the carbon vanes were falling apart.
Removed all the bits and put machine screws into
the ports in the head. Never a problem. In
fact had no real problem before, except the
vanes were crumbling and making dreadful
noises.
chuckc

I would agree that they are useless on older cars. I had a '74 260Z that all the emissions, Air pump, EGR.... were removed and when the carbs were tuned right passed smog no problem.
I disagree that all new vehicles dont have them, because alot still do. Just most are electric and they are now used on start-up. They are supposed to dump extra oxygen into the cat to light them up quicker, as cats dont operate properly unit a certain temp. That why there were alot of 80's and 90's GM vehicles had the solenoids for the airpump. When cold it had a lin run straight to the cat and then when warm dumped into the exhaust. My '01 Z28 had the electric pump and my '98 Vorteck 454 has it dumped into the manifolds.
Now the EGR, other than fouling the intake tract, I see absolutly no point to.
J Wirtes

Have you swapped out the cast iron thermostat housing with the bracket for the smog pump the engine no longer has? If not it's time you did and bought an aluminium alloy thermostat housing for the UK cars that didn't have the smog pump bracket.
Daniel Thirteen-Twelve

I have removed the air pump on the 1971 a couple of times. I missed the backfire (which is characteristic with air injection at altitude) and also noted that fuel economy dropped without the pump. The engine was certainly quieter with easier access for tuning and repair, but the car runs better and with maximum economy with the pump in place and working properly. It also looks all too original. By now, the car is on its 3rd air pump with over 250,000 miles.
Glenn Mallory

This thread was discussed between 13/07/2010 and 15/07/2010

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