What do these emmissions results mean?

[91CavGT]

II know that through an emmissions sniffer test you can tell how a vehicle is running. I know HC readings tell you how effectively the fuel is being burned (err, how rich or lean the mixture is). NOx readings are an indication of ignition timing if I remember right. What about the other readings?



These are the results from my 1991 Cavalier station wagon. It has a built 3.1L V6 that's been bored 0.030" over, it's got a custom Crower camshaft, everything has been ported, polished, and port matched, it's got 320 cc RC Engineering injectors, a Haltech E6GMX standalone computer, and a Garrett 46 trim T3/T4 turbocharger. The motor currently has about 15,000 miles on the rebuild.


25 mph test

maximum allowed results

HC ppm 120 78
CO% 0.67 0.09
CO2% 13.9
O2% 0.8
NOx ppm 848 441
Dilution% >6 14.0


15 mph test

maximum allowed results

HC ppm 124 124 <-- running a bit rich and BARELY passed
CO% 0.69 0.13
CO2% 13.4
O2% 1.5
NOx ppm 937 554
Dilution% >6 13.5



So can someone explain these in a bit more detail?

[2000mc]

hc = hydrocarbons - unburnt fuel (unless youre burning oil too)

co = carbon monoxide - goes up when youre running rich, part ofburnt hydrocarbons

co2 = carbon dioxide - part of burnt hydrocarbons, other part is water vapor

o2 = oxygen - oxygen not used by combustion

nox = oxides of nitrogen - goes up in excessive combustion temps


but i'm guessing its not running rich because youre 02% (oxygen) also went up and co is still low. apparently your engine is less efficient than normal at lower rpm(15mph test). my guess would be that your cam has a greater overlap than stock which could cause this.

[91CavGT]

I don't know the duration of the stock camshaft, but here are the lift specs.

Lobe lift intake .2626"
Lobe lift exhaust .2732"



Here are the specs from the camhaft that is currently in the car.

Intake: 284 degrees duration 0.432" lift
Exhaust: 274 degrees duration 0.417" lift


All these specs are based off of a 1.5:1 rocker ratio.



The low speed test was done in 2nd gear at 2,000 rpm. The high speed test was done in 3rd gear at about 1,800 rpm.