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Add a restricter after the cat to add backpressure... (about 3/4" hole).The backpressure will help with EGR which will reduce NOXTake out after test.
Have the same problem with my 85 22RE (cam, big valves, higher compression, & header) every smog. My NOX were at 1200. So what I did is tee into the vacuum line that goes to the EGR valve then tee in to the ported vacuum line off the throttle body & hide the vacuum line under the intake plenum. What this does is at part throttle the ported vacuum source applies more vacuum to the EGR valve than normal causing the EGR vavle to open more & that = less NOX. After the smog I take the vacuum line off and throw it in my glove box for next time. Been doing this for the last 8 years. Also what helps is making sure that the cat is real hot. I sit outside the smog shop & run the engine at 2000 RPMs untill he is ready to smog it. Good luck.
Yes, NOX emission are a product of high combustion chamber temps, not to be confused with engine temps. Raising the compression on an engine will raise combustion temps. NOX emissions are produced when the combustion temps are above 2500 degrees. What the EGR does is let a controlled amount of exhaust gas into the combustion chamber, which is inert and doesn't burn. This inert gas takes up space in the combustion chamber so less of a air fuel mixture will enter the combustion chamber, effectively lowering the compression, combustion chamber temps & NOX emissions. The reason I run the engine at 2000 RPMs before the smog is to make sure the Cat is at operating temp. Catalytic converters are more efficient when at operating temp. allowing them to burn off more pollutants (CO, HC, & NOX).
Thanks for the education. I took all of the Toyota classes through T-ten except for the smog class so smog no-how is definately my downfall. I think I'm going to try a combination of replys above.
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