sadist

Do all unleaded cars require air pumps for the extra oxygen for the cat, or is it just because rotors have hotter exhaust gases?

Also is this just for stock cat setups, ie if I get a nice 3" high flow cat will it also require the air pump?

turboren

Well, by law, in most states, you will need to keep all the treehugger stuff on your car. If your state has no emissions test, you can ditch the air pump, BUT, you will have to run a double-groove pulley on the alternator, and use two belts, so the water pump pulley will have enough contact surface to turn without slipping, especially at high rpm.

Not all cars require air pumps. In fact, most manufacturers ditched those in the late 80's. I'm not exactly sure why rotaries still have them (as far as I know), but i think it's becuse our cars tend to have a lot of unburned hydrocarbons in the exhaust.

Ren

Icemark

Here in the states it is illegal by often both the state and the federal government to remove the emissions equipment.

Of course that doesn't stop people from doing it for that last 5 horsepower, and 20 lbs. Here's a great link from the English Soarer club (Lexus SC club) on why you shouldn't however: http://www.jkwebdesign.co.uk/lexusclub/exhausted.htm

But back with the rotary, you have a couple of issues of why the air pumps are on the cars with cats.

The object is to get the cat up to temp ASAP, which the rotary does quite well with its extra hot exhaust, but the draw back is that if the engine is running too rich, and you are getting a lot of HC dumped into the Cats, since they already are quite hot to start with, now you add even more heat from the catalyst process, but you are not adding 02. O2 helps calm or balance the catalyst process, sorta like carbon rods on a Nuclear reactor. So the air pumps are used to pump fresh air containing 02 into the Exhaust/Cat to help prevent the cat from internally melting its rare earth metals into slag.

Now since most Americans don't replace the O2 sensor very often (like they should) the ECU reading that O2 sensor can often make the engine run rich... So the Air pump provides that extra little bit of help, so that the car can make it past its 100k-mile emissions warranty.