Everybody likes to breathe clean air (New Yorkers may be an exception). But there seems to be less and less of it around. Just look across Puget Sound after a few days of nice weather and you will see a brown haze hanging there - smog.

Through government regulations we are trying to do something about that, but what impact will it have on those of us who like performance cars but can't afford to buy the latest emission-controlled, computerized, catalytic-converter-equipped, twin-turbo mega-buck rocket sled? Is there performance after the emissions test for older cars? Are there even TABS after the emissions test?

Cheer up. It's not as bad as you might think. First, we'll take a look at what the standards are for emissions testing. Then we'll see what factors in our engines affect emissions. Finally we'll look at some things we can do to optimize the chances of passing the test. As you will see, some of them will actually IMPROVE your car's performance.

These are the upper limits. The DOE claims that a properly running car, tuned to the manufacturer's specs, should not exceed 300 ppm HC and 1.5% CO if it is not equipped with a catalytic converter. Those figures drop to 100 ppm HC and 0.5% CO for cars with converters. Notice that the upper limits do not distinguish between cars with catalytic converters and those without.

The two major factors that influence emissions are fuel mixture and ignition timing. The old rule of thumb has been to use an air/fuel mixture ratio of 12:1 for power and 15:1 for economy. HC emissions are lowest at about 16:1 to 16.5:1. CO emissions are fairly low and constant above 15:1 but go up rapidly below that. So a lean mixture is better as far as emissions go. But a lean mixture can be hard to ignite and an overly lean engine will tend to overheat and ping or detonate. Missing can also cause a high HC reading due to the unburned gas. Try to go as lean as you can. If you are running SU's, they are easy to adjust; other carbs require more work. Fortunately, a CO reading of 6.0% equates to an air/fuel ratio of 12.24:1, so you should be okay from that standpoint.

As for ignition timing, advance has very little effect on CO emissions, but it does increase HC output. How much it increases depends on the air/fuel ratio. At around 16:1, the HC emissions at 40o advance are more than double what they are with 20o advance. At 12:1 the increase due to the same advance is more like 50% but the overall HC is still much higher than at the leaner ratio. The bottom line is, the less advance, the less HC.

A certain amount of engine oil will be burned even in a fresh engine. The cleanliness of this oil can affect emissions readings. If the oil is really grubby, change it before you go in for the test.

There are other factors affecting the richness of the mixture besides the jetting. A dirty or plugged air filter will cause an artificially rich condition. Install a clean filter before you go in for the test. Better yet, install a low-restriction unit like a K&N filter and pick up a couple of horsepower in the bargain.

Usually an engine runs a lot richer on the idle jets than it does on the primary circuit. You might be able to get off the idle jets by raising the idle speed, but it has to be under 1000 rpm or they won't run the test.

One cause of HC emissions at idle is weak or inadequate spark. High compression and a lean mixture will make it harder to get full ignition, as will fouled spark plugs. A long-duration or multiple-spark ignition system like those made by Crane or MSD will assure more complete combustion at low rpm and clean up some of those HC problems, in addition to giving you more power and cleaner spark plugs. Make sure you have fresh plugs in the engine for the test.

A more subtle factor that affects HC emissions is cam timing. Long duration cams with lots of overlap (where the intake and exhaust valves are open at the same time) increase HC because unburned fuel flows directly from the intake to the exhaust. This is great for top-end performance because it cools the exhaust valve and helps scavenge the cylinder of the waste gases from the previous power stroke. But it can kill you at the testing station.

Can you do anything about it? Yes. High-revving engines with heavy valve springs are notoriously hard on valve seats. The valves pound away at the seats and sink into the head. This tightens up the valve lash. Since many of these cams have long ramps at the ends of the valve events, this decreased clearance will actually increase the effective cam duration and consequently the overlap increases, too. In addition to increasing HC, this can also hurt low-end performance. Make sure your valves are adjusted correctly to prevent excessive overlap.