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Does a GT3 have a "smog pump"


navin in KC

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I am a C4S owner and I am looking to move what I believe is called the "smog pump" or maybe it is an "air pump". Here is a picture of it:

dyx5jm.jpg

I am hoping a GT3 has the pump mounted further to the left of the car, in behind the left taillight. If it is mounted there, I could get the GT3 bracket and use it to reposition mine.

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I believe that all current NA (996's) have an auxiliary air pumps. I'm not sure about the turbos. 996's do not have "pre-catalysts" like a lot of cars are getting these days. Pre-cats are placed close to the exhaust manifold and designed to clean up the extra dirty exhaust that is emitted during cold start due to cold and inefficiently burned gas. They also introduce some amount of extra restriction in the exhaust tracts. 996's do have regular/main cats that introduce very little restriction. To deal with the dirty start-up situation, 996's (including GT3's) have an auxiliary fresh air pump (what your picture is pointing at) controlled by the ECU that injects fresh air into the exhaust system right at the exhaust ports in the heads. You can see the injection ports in the heads if you remove the exhaust manifolds. There are even "reliefs" in the gasket to circulate the fresh air among the ports. The fresh air will mix with the hot, unburned hydrocarbons at cold start and burn them in the exhaust manifolds. It sounds like popping/rattling on start up, especially on a GT3. The ECU runs this until things warm up...usually up to 2 minutes depending on engine temp. This is a Good Thing! The pump is electric and saps no horsepower...and the whole thing is over in a minute or two. Boxsters have pre-cats in their exhaust manifolds and they "look" very restrictive. The 996 "air pump" is nothing like the old "smog pumps" of the '70's.

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