SMOG before and after downpipe

Oct 11, 2005
3,819
20
38
Thousand Oaks, CA
Thought it would be interesting to compare my emissions with and without the 1st cat.

Bottom line, removing the 1st cat increased my HC and NO significantly. My low speed HC is now at 80% and that is a little too close for comfort. I've seen my HC emissions climb with every test since they started in 99. If you are marginal, you will want both cats to pass. No doubt lightoff emissions are horribly worse too, but since that is not tested for, only you will know!

The % of pass limit is shown in brackets

Two cats:
HC 15mph: 51ppm (48.1%) 25mph: 23ppm (28.4%)
CO 15mph: 0.02 (2.9%) 25mph: 0.01 (1.8%)
NO 15mph: 2ppm (0.3%) 25mph: 2ppm (0.3%)


One cat:
HC 15mph: 85ppm (80.2%) 25mph: 41ppm (50.6%)
CO 15mph: 0.08 (11.4%) 25mph: 0.02 (3.5%)
NO 15mph: 153ppm (20.1%) 25mph: 50ppm (7.1%)

Still, not too bad for a 17 year old converter.