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Artifex · 09-20-2006, 09:27 PM

Emissions
The last part that everyone with state inspections must pass is the tailpipe emissions test. There are several gasses which are tested by the state ref, and all of them are related to ecological effects. A sophisticated gas analyzer is used to measure the results, and if the car generates too much of any particular compound, the car will fail.

I have seen 2 varieties on how this is done. The first variety is done in a garage with the car in neutral. The engine is revved up to probably a max of around 3500 RPM, but for the most part the car is measured at idle. This is the easiest test to pass. When the car is not under load, it does not use much fuel, and the emissions are naturally low. Hondas are particularly good at this, since they are efficient engines by design, and have low idle RPMs. Only older cars have any trouble passing this test.

The second variety uses a chassis dyno during the test. This test is harder to pass, since the emissions are measured while the car is under load. When the engine is loaded, it burns more fuel, and is going to generate more particulate emissions. Not many states use this method currently, because it requires all testing stations to have dynos, which are expensive. However, I believe that more states will transition to this measurement in the future.

Breathing modifications (intake/exhaust) tend not to affect emissions adversely. The biggest issue is the catalytic converter. Hi-flow cats, or no cat, will directly affect emissions. High flow cats have smaller internal surface area, and will treat a smaller volume of exhaust gas. More exhaust particles will pass through the cat without being converted to harmless compounds. No cat will very obviously allow all combustion byproducts to pass straight through the tailpipe. Many people report that high-flow cats will pass emissions testing (I have done this myself). No cat will most likely fail completely (if it doesn't fail the OBD2 part above).

If you have a car that needs to pass the emissions criteria, there are a few things you can do to improve your chances. I am going to list all of the techniques I know of here:

1) Make sure your spark plug wires and plugs are new. A good ignition system helps to pass.
2) Try burning off some of the internal carbon in the motor by using an engine cleaner like Seafoam.
3) Make sure the catalyst is nice and hot. A hot catalyst is more effective at eliminating particles. You can do this by driving the car hard, which passes hot engine gas through the catalyst as long as possible.
4) Fill up your tank with part ethanol. Ethanol produces less particulate emissions than gasoline. Unless your fuel system is modified to handle it, don't use more than 30% ethanol.
5) There are some commercial fuel additives which claim emissions benefits. I have not tried them, but I know several people who were successful with it.
6) As a last resort you can adjust your ignition timing. There are certain ignition timings which yield lower emissions, and are not necessarily correlated to best torque, or best EGT.

09-20-2006, 09:27 PM	#3 (permalink)
Artifex Retired PO Adminsicle Join Date: Jun 2002 Location: San Jose, CA Posts: 2,535 iTrader: (0)	Emissions The last part that everyone with state inspections must pass is the tailpipe emissions test. There are several gasses which are tested by the state ref, and all of them are related to ecological effects. A sophisticated gas analyzer is used to measure the results, and if the car generates too much of any particular compound, the car will fail. I have seen 2 varieties on how this is done. The first variety is done in a garage with the car in neutral. The engine is revved up to probably a max of around 3500 RPM, but for the most part the car is measured at idle. This is the easiest test to pass. When the car is not under load, it does not use much fuel, and the emissions are naturally low. Hondas are particularly good at this, since they are efficient engines by design, and have low idle RPMs. Only older cars have any trouble passing this test. The second variety uses a chassis dyno during the test. This test is harder to pass, since the emissions are measured while the car is under load. When the engine is loaded, it burns more fuel, and is going to generate more particulate emissions. Not many states use this method currently, because it requires all testing stations to have dynos, which are expensive. However, I believe that more states will transition to this measurement in the future. Breathing modifications (intake/exhaust) tend not to affect emissions adversely. The biggest issue is the catalytic converter. Hi-flow cats, or no cat, will directly affect emissions. High flow cats have smaller internal surface area, and will treat a smaller volume of exhaust gas. More exhaust particles will pass through the cat without being converted to harmless compounds. No cat will very obviously allow all combustion byproducts to pass straight through the tailpipe. Many people report that high-flow cats will pass emissions testing (I have done this myself). No cat will most likely fail completely (if it doesn't fail the OBD2 part above). If you have a car that needs to pass the emissions criteria, there are a few things you can do to improve your chances. I am going to list all of the techniques I know of here: 1) Make sure your spark plug wires and plugs are new. A good ignition system helps to pass. 2) Try burning off some of the internal carbon in the motor by using an engine cleaner like Seafoam. 3) Make sure the catalyst is nice and hot. A hot catalyst is more effective at eliminating particles. You can do this by driving the car hard, which passes hot engine gas through the catalyst as long as possible. 4) Fill up your tank with part ethanol. Ethanol produces less particulate emissions than gasoline. Unless your fuel system is modified to handle it, don't use more than 30% ethanol. 5) There are some commercial fuel additives which claim emissions benefits. I have not tried them, but I know several people who were successful with it. 6) As a last resort you can adjust your ignition timing. There are certain ignition timings which yield lower emissions, and are not necessarily correlated to best torque, or best EGT. __________________ Ken I am no longer an active member of the moderation team. Please contact another mod if you need help with anything. 2000 Base Prelude RIP Pics of Jessica Alba naked! Last edited by Artifex : 09-20-2006 at 11:28 PM.