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Correct. The catalyst effect in the cats doesn't happen until they are above a certain temperature. The air pump is to the cat lattice as your mouth blowing is to freshly lit kindling for a campfire. Once the cats reach temp they ignite and convert unburnt hydrocarbons without need for additional O2 to help. It should be noted that engines produce the most emissions per unit of time during start up, thus this specific air-pump solution to reduce them. The illustration below also illustrates why cars with cats make all the "white smoke" (water vapor exiting the tail pipe condensing to form a cloud on a cold day...then quickly evaporating again due to the typical dryness of cold air). Catalytic converters were and are a kind of miracle of science that produce a HUGE benefit with a very low performance penalty. I almost said cost, but platinum is the typical catalyst...and this is why good cats are expensive. But here again it's a win, because catalysts participate in reactions without being consumed, so a well made cat is good for a long time.
Originally Posted by davek9
OP Its your car do as you like, the point is it's not needed, especially if you don't run CATS or run the newer Hi performance CATS.
I was always under the impression that the Air Pump only pumps air to the CATS during Warm Up to assist them in getting up to Hi Temp, once the engine is running at Temp, the Air pump is diverted to the Intake Air-box.
Newer CATS do not require this extra Air to get them going and that is why we no longer have Air pumps on new cars.
Can anyone verify that?
I remove the good ones and box them up to, along w/ the CATS
On the one hand, I live within the overall boundaries of a state park and appreciate our pristine environment. On the other, I have few neighbors, and we certainly have no smog problem. Our only air pollution comes from the smokestacks of upwind states....
I took out the air pump when I put in a Portensioner. I took out all the other stuff when I removed the right-side valve cover, which is difficult enough without it. It's all in the "California box".
The only issue is my wife does not appreciate the smelly exhaust during start-up; I must endure dirty looks.
I have an air-cooled 911, and I get dirty looks for it, too!
Try smelling a Euro 928 with no cats. FWIW, I removed my air pump setup after the pump started making noises. In the Euros with no cats, the air pump is plumbed into the heads. I'm not sure what that really did other than mix some fresh air into the smelly exhaust, maybe to make it less smelly!
Try smelling a Euro 928 with no cats. FWIW, I removed my air pump setup after the pump started making noises. In the Euros with no cats, the air pump is plumbed into the heads. I'm not sure what that really did other than mix some fresh air into the smelly exhaust, maybe to make it less smelly!
The pump was intended to add O2 to the combustion process to achieve a higher temperature to burn the exhaust gasses hotter and cleaner. Like a bellows on a forge.(Not sure if this is the case with 928's but with my experience with 911 cars and others) the pump injected air into the exhaust manifold or the cylinder head combustion chamber to achieve this process. I'm new to the 928 scene so I'm not sure how the process works on these cars yet. I just bought two 928's a 80 and a 84s.
Okay, to show you guy's what a dumb *** I am when it comes to 928's. ( I just purchased my first three months ago) . I just noticed that the smog pump belt drives the cooling fan so what can I do to eliminate the pump and keep the fan working?
Okay, to show you guy's what a dumb *** I am when it comes to 928's. ( I just purchased my first three months ago) . I just noticed that the smog pump belt drives the cooling fan so what can I do to eliminate the pump and keep the fan working?
A. Get a factory pump delete bracket with pulley - I heard a rumor 928 International has a couple
B. Shorter belt - 928 International & 928's R Us most likely know the exact belt you need.
C. Ditch the mechanical fan & go with an electric setup.
The pump is pumping air into either the combustion chamber or post exhaust (not sure on 928's yet as their new to me) to burn more completely the unburnt gasses.Blowing O2 on a fire makes it hotter. The 911' s (that I'm proficient with been working on them since the 70's) had a smog pump and thermo reactors and the extra heat generated by these devices would destroy the engine because of the excess heat. This was done to satisfy CAFE standards in the US and it almost put Porsche out of business.
If you turn the air pump by hand you notice how smooth it operates. Like a disconnected alternator. So I believe no horsepower lost here. The air is directed into the exhaust ports inside the cilinder head to burn off unburnt gas. Afterburning to clean your smoke.
My euro 928 has this system. No cats. I keep it on the car to have a cleaner ride.
If you turn the air pump by hand you notice how smooth it operates. Like a disconnected alternator. So I believe no horsepower lost here. .
A 200 amp alternator running at 12 volts consumes close to 4 bhp. An air pump when spinning at some speed close to the engine speed for sure will consume some power but not much in the big picture of things or so I suspect. Remember when you turn it by hand you are not imposing any significant load on it so no noticeable resistance to motion.
01-09-2018, 08:15 PM
