Fun with Emissions
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Joined: Sep 1999
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From: Phoenix, Arizona, USA
Fun with Emissions
Just thought I would share my latest dealing with Arizona emissions standards with everyone. This will also show that you can pass the testing without an EGR valve. I am guessing that Arizona tightened the limits in the last 2 years because I had no problems passing 2 years ago with the same engine.
My initial readings were HC: 0.62 (1.0 limit), CO: 8.86 (12.0 limit), and NOx: 3.37 (2.5 limit). I soon discovered that the EGR system is the primary system to fight the NOx levels. My engine uses the GM Performance Parts L98 heads. These heads have no center exhaust passage; therefore, I have no functioning EGR system. The only other ways I figured that I could battle the problem was through ignition timing and maybe the catalytic converter.
My engine combination (see my signature/profile) does require me to run a considerable amount of timing advance (that is a whole different story). The reading shown above are with the timing set at about 14-16 degrees advanced with the computer bypassed.
I retarded my timing down to 8 degrees advanced and my readings were HC: 0.8, CO: 5.41, NOx: 2.82. I now decided that maybe the Dynomax high flow catalytic that had been on the car for about 4 years might need to be replaced. Ordered a new unit and got it installed. With the timing still at 8 degrees the readings were HC: 0.29, CO: 0.83, NOx: 2.53. That night I retarded the timing down to 0 degrees (stock setting, car runs like crap) and the reading were HC: 0.26, CO: 0.86, NOx: 2.29. Finally passed.
I understand the corvettes that came with these cylinder heads used some sort of externally connected EGR valve, but I have not had any strong reason yet to try to hook it up. This whole experience has certainly made me think about it. Hopefully, my findings here might be able help out someone else experiencing similar problems.
My initial readings were HC: 0.62 (1.0 limit), CO: 8.86 (12.0 limit), and NOx: 3.37 (2.5 limit). I soon discovered that the EGR system is the primary system to fight the NOx levels. My engine uses the GM Performance Parts L98 heads. These heads have no center exhaust passage; therefore, I have no functioning EGR system. The only other ways I figured that I could battle the problem was through ignition timing and maybe the catalytic converter.
My engine combination (see my signature/profile) does require me to run a considerable amount of timing advance (that is a whole different story). The reading shown above are with the timing set at about 14-16 degrees advanced with the computer bypassed.
I retarded my timing down to 8 degrees advanced and my readings were HC: 0.8, CO: 5.41, NOx: 2.82. I now decided that maybe the Dynomax high flow catalytic that had been on the car for about 4 years might need to be replaced. Ordered a new unit and got it installed. With the timing still at 8 degrees the readings were HC: 0.29, CO: 0.83, NOx: 2.53. That night I retarded the timing down to 0 degrees (stock setting, car runs like crap) and the reading were HC: 0.26, CO: 0.86, NOx: 2.29. Finally passed.
I understand the corvettes that came with these cylinder heads used some sort of externally connected EGR valve, but I have not had any strong reason yet to try to hook it up. This whole experience has certainly made me think about it. Hopefully, my findings here might be able help out someone else experiencing similar problems.
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