Artifex's guide to passing smog - Honda Prelude Forum

Artifex · 09-20-2006, 08:12 PM

I was chatting with alphajesse, and it occurred to me that there would be some value in making a formal posting on how to deal with smog inspections that performance users will face. I intend this to be a survey of the different options available to people, and not as a sure fire method of passing.

I want to state for legal reasons that this is not an endorsement of violating state emissions laws. I leave it up to the user to make their own choices, keeping in mind that there are legal and ecological consequences to circumventing emissions devices.

Passing smog is a concern of both N/A and F/I cars. Most of the content here will be Honda specific, although I suppose you can apply this to anything. There are 3 different domains that are of concern, and I will give an overview of each one and possible solutions. Some of these 3 domains may not apply to you, depending on which state you live in.

Visual
The visual inspection, as far as I am aware, only applies to residents of Cailfornia. Users from other states can skip this and read the next section. In CA, emissions rules are controlled by the California Air Resources Board (CARB). A visual inspection can be done by police officers on the street, or official smog refs designated by the state. In CA, it is legal for police to search your car whenever they want, and I believe drivers cannot refuse this request (it is an offense to refuse). The only area for concern are engine modifications; transmission and suspensions mods don't affect emissions, and generally CARB doesn't care about them.

The goal here is to be very low key in how you upgrade your car. There are some upgrades that can't be detected by visual inspection, such as internal engine mods or ECU upgrades. The mods that are the most likely to fail are turbo kits and exhaust modifications, because they really can't be hidden in any way. For the most part, if it can't be seen by looking, you won't have trouble with the Visual.

Another major option is to buy upgrades that are approved by CARB. Aftermarket companies, if they pay money and go through state testing, can ask CARB to approve their products for street use. Unfortunately, there aren't many CARB approved products. Some of the ones that are available suck (IMO), so that's no good either. Generally, it is rare to find one that is CARB approved and useful. It's all a big racket really, it's another method for the state to rubber stamp stuff by extorting money from the aftermarket.

The last thing I will mention is a dirty trick you can pull (if you are lucky). I am not endorsing this method, but it may work. You can find the little CARB approval badge which comes with approved aftermarket parts. If you take this badge and duplicate it, you can apply it to your current parts setup. This will fake out the police, but it will not get you past CA smog refs.

Artifex · 09-20-2006, 08:27 PM

OBD2 Compliance
The 2nd big domain is OBD2 compliance. If your Honda is younger than 1996, this doesn't apply to you. This is a concern in many states, and the number of states adopting OBD2 testing grows every year. If you don't have to get OBD2 tested this year, you may end up needing this next year, so don't discount OBD2 automatically. OBD2 is a technology mandated by the government, to improve the early detection of electrical and mechanical problems in the car. The Engine Control Unit (ECU) provides this feature. Overall, this technology is very useful, but it presents issues for the performance aftermarket.

This is a problem, because any real aftermarket ECU for Hondas don't provide OBD2 compliance. The most popular ECU mod is a conversion to OBD1 (which is programmable), which clearly means that OBD2 capability is lost. Other high quality standalones (AEM EMS, Autronic) don't support it, and have no intention of supporting it. Therefore, this is a big concern when upgrading the ECU.

There are some ECU upgrades which keep your original ECU, and these are known as piggybacks. These devices generally make less power, but they are easier for end users to install. Using one means you can preserve the OBD2 feature of your stock ECU. It is also worth adding here that there used to be a lot of discussion here about the "OBD2 workaround" (the original text was taken down). It is important to note that the workaround is not reccomended anymore, because it messes with the LTFT settings. The "workaround" also messes up the driving cycle, which is a test that the ECU does after it has been reset. The driving cycle is a small period of time it takes for the ECU to measure all the sensors, and set all the ready codes. On the Prelude ECU, this takes about an hour. Not hard to do for an annual inspection.

The basic premise of OBD2 testing is that officials will plug in special scanning equipment into the OBD2 port of your car. They will read out information stored in the ECU, and make sure the ECU doesn't indicate any error conditions or warnings. For the most part, the emissions techs rely exclusively on the data coming back from the ECU. If the ECU says everything is kosher, the tech will sign off.

So the real question is: how to we provide an OBD2 data port for the techs? There are 2 ways to do this. The first is not common, so I'll only mention it briefly. You can run a newer OBD2 ECU, which are programmable (Flash-based). This only applies to cars newer than 01, so it usually won't apply. One solution I haven't yet seen is to adapt a newer 01+ ECU to run an older motor. Theoretically it can be done, but I haven't seen this yet. The other more feasible solution is to run the original ECU during the short time the car is in for smog testing. This works, but you have to be very careful about how you do it.

For an N/A car, it's relatively easy. Even with some extensive N/A mods, the car will run on the stock ECU. The stock ECU will control injectors up to 20% larger with the proper learning. The key factor here is to keep the care in closed-loop when driving. On a Prelude ECU, this means keeping the throttle under 33% open, and keeping the RPMs under 4000. This forces the ECU to use the O2 sensor to keep the AFRs around stoich, which will mean the ECU will compensate for any intake/exhaust flow differences (or anything else).

For F/I cars, this can still work. The biggest issue is how to handle the fuel system. If your injectors are more than 25% larger (nearly always true), then the stock ECU won't be able to handle them. The simplest solution is to put back the OEM injectors to get smogged. Make sure to install the original ECU at the same time. The second key to making this work is to keep the car out of boost. For turbo cars, this means forcing the wastegate open all the time. This can be done with a length of bailing wire, available at Home Depot. Just wire the wastegate arm all the way open, and the turbo should stay off boost. For external wastegate, there should be a way to do it, but I don't know it offhand. For a supercharger, there should be a way to force the bypass valve open all the time. If that isn't practical, you can also take the drive belt off.

The last thing to remember is to complete the driving cycle.

Artifex · 09-20-2006, 08:27 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.

Phat8186 · 09-20-2006, 09:01 PM

Very good information to know thanks
Ken

TwizT · 09-21-2006, 12:00 PM

Good work

This should be stickied or FAQ'd