MONGO510 Posted June 21, 2012 Share Posted June 21, 2012 I need to clean up my exhaust to pass a smog test. I have a Comp 280 cam that idles pretty rough. I am thinking that if I advance the timing It will raise the vacuum levels and help to smooth out the engine, thus reducing the HC levels. i can then lean it out and get passing CO levels Ideas? I can get pretty close but no cigar yet. Quote Link to comment Share on other sites More sharing options...
Leon Posted June 22, 2012 Share Posted June 22, 2012 Leaning out plus advancing timing will considerably increase NOx formation. I doubt you'd pass the test if there is a NOx requirement. Otherwise, leaning the mixture out will reduce CO and HC but HC is also a result of having a cam with more overlap. You may have to put in a stock cam if you can't pass the test. Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted June 22, 2012 Author Share Posted June 22, 2012 Thanx for t5he reply Leon. Nox is not tested. As a matter of fact they don't check idle speed or even pop the hood. Their only concern is that it have a "cat", if it had one originally. As long as it can meet CO and HC and noise standards, its a go. They don't care what engine is in it either. My engine is producing 15" in. of vacuum, which is a little low, I think if I advance the timing a few degrees I may get a little more vacuum, which should help smooth the Idle, allowing me to lean it a bit. Your thoughts are appreciated. John (Mongo) Leaning out plus advancing timing will considerably increase NOx formation. I doubt you'd pass the test if there is a NOx requirement. Otherwise, leaning the mixture out will reduce CO and HC but HC is also a result of having a cam with more overlap. You may have to put in a stock cam if you can't pass the test. Quote Link to comment Share on other sites More sharing options...
Leon Posted June 22, 2012 Share Posted June 22, 2012 Thanx for t5he reply Leon. Nox is not tested. As a matter of fact they don't check idle speed or even pop the hood. Their only concern is that it have a "cat", if it had one originally. As long as it can meet CO and HC and noise standards, its a go. They don't care what engine is in it either. My engine is producing 15" in. of vacuum, which is a little low, I think if I advance the timing a few degrees I may get a little more vacuum, which should help smooth the Idle, allowing me to lean it a bit. Your thoughts are appreciated. John (Mongo) You can increase timing and lean it out if you just want to reduce CO and HC, although I wouldn't expect a drastic reduction in HC (CO will drop to an acceptable level). HC levels will largely depend on valve overlap, and you can't change that without putting a different cam in. Try to lean it out (without misfire of course) and see what happens, but as I said earlier, don't be surprised if you have to reinstall a stock cam in order to pass. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted June 25, 2012 Share Posted June 25, 2012 Find out the highest idle you are allowed. Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted June 26, 2012 Share Posted June 26, 2012 I used to do smogs in cali but I dont know what oregon tests for.If its just HC & CO put enough ignition timing on it to run as smooth as possable and lean it out-but just before a lean miss.I run my l28 turbo at 18btdc .Also run the idle up to 1000 rpm or so if they will allow it.If the cat is hot it should pass Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 26, 2012 Share Posted June 26, 2012 Yep, I'm with Randy--idle in the 1000 to 1100 range if they allow it with the minimum timing you can get to run smoothly, then adjust for 'lean best'... A 1973 240Z adjusted in that matter using 72 Round Tops and AIR into one collector tube of the header (no EGR) piped clean to 83 Catalyzed standards! Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted June 28, 2012 Author Share Posted June 28, 2012 I increased timing to 12 degrees, set idle at 1200, leaned it to just before missfire. While waiting in line I ran the engine at 2500 rpm. When I pulled in for the test , the cat was blistering hot and it passed easily. They never checked under the hood,never checked idle speed, and they new it was a Chev motor. As long as it had a cat and good #'s all was well. Quote Link to comment Share on other sites More sharing options...
Leon Posted June 28, 2012 Share Posted June 28, 2012 I increased timing to 12 degrees, set idle at 1200, leaned it to just before missfire. While waiting in line I ran the engine at 2500 rpm. When I pulled in for the test , the cat was blistering hot and it passed easily. They never checked under the hood,never checked idle speed, and they new it was a Chev motor. As long as it had a cat and good #'s all was well. Nice! Quote Link to comment Share on other sites More sharing options...
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