Help interpret change in emissions test readings

[Cattler]

I just passed my Virginia emissions inspection, but noticed that the readings are much higher than when the car was last tested (2007) and am wondering what these readings might mean. Since 2007, I've had the car "tuned up"--new rotor, distributor cap, plugs, wires--and replaced my muffler with a new stock Dansk unit. The old muffler had rust pin holes in the bottom.

Here are my readings:
Type (15 mph) Limit 2007 reading 2009 reading
HC ppm 86 26 75
CO % 0.34 0.12 0.18
NO ppm 1125 283 617

Type (25 mph) Limit 2007 reading 2009 reading
HC ppm 156 28 144
CO % 0.50 0.20 0.47
NO ppm 1094 350 1067

Thanks,
David

[Cattler]

Anybody?

It was ~100 degrees here yesterday when I went for the test and I had the engine at full normal operating temperature. Maybe these readings are so much higher because I took the car in 2007 in the morning (colder ambient temp) and I know the engine wasn't warmed up.

[86 911 Targa]

Cattler,

I think you answered your own question.

Emissions will vary as function of both engine,
ambient temperatures, and condition.

Higher cylinder temperatures burn off the "bad stuff"
better than low temps.

This is why the "Detroit Folks" installed higher temp
water thermostats in the 70's.

However, the work you performed on your car is also
a meaningful variable and, may have impacted the numbers.

So you may be comparing "apples with oranges".

Also, if you used the same test station, the numbers are
well within the measurement error(s) of the test equipment,
which may have been re-calibrated since your original test.

The only way to conduct a measurement error analysis/repeatability
test, is to re-run the test(s) back to back under the same ambient conditions,
with your car at the same operating temperature, and the identical test station.

I always get tested with the engine temp @210F.

Gerry