Contour Enthusiasts Group Archives Forums General Troubleshooting Emissions law question........

Originally posted by Big Jim:

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The main reason that the precats are there is to help clean up the emissions during warm up. However, they work all the time and make a significant contribution to clean tailpipe readings. With the precats in place, all cats healthy, and a healthy running engine, the tailpipe readings will be nearly zero. If only the main cat is functioning, the readings will be on the high end of spec and if all goes well will pass the test.

Some cars have used an electric air pump to add a bit of fresh air during warm up instead of precats. Volvo used it for a few years, as did the Lincoln Mark VIII. I don't know if it ever went into production, but there was talk of Fararri using two stage headers with a valve similar to the old style heat riser. During warm up the exhaust is to be routed through the precat and after warm up the precat is bypassed.

One of the dirtiest modes of operation is warm up.

Remember that the method of measuring exhaust emissions to get a car certified by the manufacturer, is to drive it on a dyno that is computer controlled and goes through a sequence of driving cycles. During portions of those tests, all of the stuff coming out of the exhaust is collected into a bag and then the bag contents analysed to bring it into a grams per mile reading. Early in the emissions game, the low hanging fruit was picked. Now the emphasis must be on getting everything as clean as possible even in the dirty modes that were harder to get under control. They must continue to find ways to clean it up.

In the early days of smog control, the emphasis was entirely on meeting the standards. Horsepower was curtailed in the rush to clean things up. The amazing thing about today is that not only are the cars much cleaner, they also run and perform much better.

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