Watching Your CARBS

The 4-1-1 on REALLY “Street Legal” exhaust components

Frank Bohanan - August 09, 2012 10:00 AM


Vehicles subject to emissions regulations (PCMVs) can have quite a bit of emission-related “plumbing” which must be retained for true legality. Here we see everything from a PCV breather tube at the throttle body to various components of the air injection system.


Due to compromises necessary for mass production and cost, factory headers tend to be far from optimal designs for performance. It’s easy to see why these Hedman headers will perform better: The bends are smooth, there are no notches for fastener clearance, the larger tubes are more equal in length, and there is a more efficient design where the tubes merge.


Note the much larger and smoother entry into each tube versus the small, stepped, and abrupt entry of the stock parts. The Hedman parts also have a sealing bead and a stronger flange.


While the sealing beads on the Hedman headers will greatly reduce the likelihood of exhaust leaks, the use of a proper gasket and the correct bolt torque are most critical. These OEM “grafoil” gaskets don’t require retightening after first use and hold up well. Be sure to check the gasket openings are larger than the ports if you’ve enlarged them.


To improve access for tightening, Hedman provides these smaller diameter fasteners with their headers. They’re not only easier to get to but their looks also hold up better. It’s a good idea to use anti-seize compound on all the fasteners to ensure easier removal.


The Hedman headers really are completely legal in all 50 states, plus they significantly improve performance and probably even fuel economy (at least a little). After some minor bending even the oil dipstick/bracket fit fine. We decided to wrap the clutch cable and bend its bracket back a bit to avoid problems.


Always be sure to secure any parts that are loose enough to possibly make contact with the headers while driving, etc. We had to remove the OEM support bracket for the air injection tube so we secured it with a zip tie (wire could also be used if it gets too hot).


This 50 state legal crosspipe from Magnaflow has larger tubes, smoother bends and less restrictive converters for much better performance versus the OEM H-pipe. It’s made of stainless steel for durability and uses a three-piece design for much easier installation. It provides for the oxygen sensors and air tube while also being lighter and smaller for better packaging. The crosspipe design also provides a more unique sound.


CARB’s new regulations for catalytic converters require they be permanently marked with their EO number so technicians/inspectors can easily see they’re legal for the vehicle they’re on. They also have to meet much stricter efficiency and durability requirements.


When reconnecting the air injection tube to the mid-pipe’s crossover tube it’s best to only tighten it until it’s just tight enough to seal but not so tight it will be hard to remove. The special design of the OEM clamp helps avoid such issues but care is still needed.


The finished installation looks great and doesn’t hang down any lower than the OEM H-pipe. The rear outlets are in the same position as on the OEM pipe so any cat-back system, OEM or aftermarket, intended for this vehicle will fit just fine and likely be legal.


With only a few rare exceptions, cat-back systems are mostly free from regulation in terms of emission compliance. Of greater relevance are state vehicle code requirements and local sound limits, which may somewhat restrict what you can possibly install.

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A lot of parts manufacturers, as well as many in the media, state some aftermarket parts are “street legal” when they really are not.

While not intentional, this still can end up costing the purchaser of these products dearly if they are fined, fail mandatory emissions tests, and/orhave to replace these parts with something else. The applicable rules are very complex on the national level and can be further complicated at the state level. While greatly varying levels of enforcement allow some to get away with just about anything, others in California and the many “green” states which have adopted California’s emission standards are far less able to do so. At least legally.

Since exhaust systems are often the area that’s most in conflict with the applicable regulations, we’ll go through a typical exhaust system and try to better explain what may or may not be possible in terms of modifications. We clearly can’t go into every detail or be specific for every vehicle in the space available, but we can provide some general guidelines to help you stay on the right side of the law, especially if you’re in a strict enforcement area.


The Basics

All 1966 and later domestic passenger cars and light trucks originally sold in California are “pollution-controlled motor vehicles” (PCMVs), and thus are subject to the applicable emission requirements. For imported vehicles and those originally sold in the rest of the country, the starting model year is 1968. What this means, in the most simple terms, is that whatever emission controls came on the vehicle when it was new must remain on the vehicle unless the vehicle is being used for racing or some other “exempted” purpose such as parades, etc.

Fortunately, there is a process for allowing legal removal of many of these parts and replacing them with something else if the proper procedures are followed. We’ll get into that in a bit. The bottom line is it is against federal law, in ANY state, to “remove, disconnect, or otherwise render inoperative a required emission control device” UNLESS the car is specially registered (historic/collector/show vehicle or similar, in most states), is being used for an exempted purpose such as racing, and/or is not being driven on public roads.

If the vehicle is not specifically exempted from this requirement by virtue of how it is registered and it is driven on public roads, you can still be in violation of federal law and can also be cited in many states, even if the vehicle isn’t required to undergo mandatory emission testing. Technically, that’s the law. Practical enforcement of it in the real world greatly varies.

Using the state of California as an example, say you have a ’69 muscle car that came with an air pump and it’s registered for use on public roads. It’s not a race car, not specially registered in any way. This car is not required to go to the state’s mandatory “Smog Check” emission testing program because it’s a 1975 or older model year vehicle. It used to be a “rolling” 30-year exemption from testing in California, and it still is a rolling (25 model years or so) cut-off in many states. The point is that even though the vehicle isn’t required to be tested, you still can get in trouble if you remove the required emission controls and/or the car is what’s called a “Gross Polluter” (a relatively high emitter but not necessarily a car that smokes).

In California and some other states there are roadside “remote sensing devices” (RSDs), which can actually sample your tailpipe emissions as you drive by them. They even take a picture of your license plate so you can be contacted later. In some places it’s just for “educational” purposes (i.e., you’ve got a really dirty exhaust and they’d really appreciate it if you’d fix the vehicle so it’s cleaner). In other places this data is used for enforcement in that if you pass by any RSD and show high enough emissions often enough, you may be required to take an emission test even if you’re not required to yet, or ever (known as an “out of cycle” test). If you fail the emission test then you may not be able to register/drive the vehicle until you get it fixed and pass the test.

For newer cars it can get even more sophisticated. If your car’s “OBD” (On Board Diagnostic) system (which operates the “check engine” light on the dash) detects a “problem” and sets a “DTC” (Diagnostic Trouble Code) or fails to set a “readiness monitor”, then you can also fail the emission test even if they only plug into your OBD connector and don’t even do a tailpipe emission test.

It’s already possible with systems such as OnStar to obtain this information remotely (and continuously), such that the status of your OBD system (as well as other monitored parameters like vehicle speed, etc.) can be accessed for either repair/maintenance purposes or, someday, potentially for enforcement purposes as well. The technology is there; just look at the insurance companies that offer a discount if you agree to let them monitor your driving via a device you plug into the OBD port.

GM monitors your data so it can contact you if there’s a DTC/problem or you’re coming up on a scheduled maintenance, etc. There are those in various state legislatures (such as California) who view access to this data as a more efficient and effective way of keeping cars clean than by trying to snag the polluters with RSDs or regular emission tests. Fortunately, privacy concerns have stopped this, so far.

Lastly, some states (such as California) authorize any “peace officer” (which is much more than just the local police and the highway patrol) to issue a citation if they determine you’re not in compliance with state law. Say you get pulled over for a burned out taillight (or whatever) and the officer thinks the car is too loud so he/she bangs on your catalytic converter can and determines it’s empty; you’ve hollowed it out. Or you let him/her check under the hood and they find stuff that’s supposed to be there is missing and/or stuff that’s not supposed to be there (such as a non-exempted power adder) is there.

And, yes, they actually do train them for this. California alone has spent millions of dollars to teach officers what to look for so they can give you a ticket and make their investment pay off. You can get some pretty heavy fines for such things and the manufacturers of the parts can really get slammed as well; some already have, to the tune of millions of dollars.

What’s legal and what’s not?

First, you don’t remove any required emission controls (just look at the underhood “Vehicle Emission Control Information” label or a service manual, etc., to see what’s required for your car) UNLESS you’re either going to replace them with what is legally considered to be a “direct replacement” (functionally identical), “consolidated”/universal (functionally equivalent), or exempted “add-on/modified” part (basically everything else that’s been shown to not increase emissions).

If a part isn’t a replacement or consolidated part, the best thing to do is to see if the part has a CARB (California Air Resources Board) “EO” (Executive Order) number. If it does, you’re good to go in any state since the U.S. EPA also accepts EOs as proof of compliance with federal requirements. If a product doesn’t have an EO then it may only be acceptable/legal in states other than California and the “green” states (mostly in the Northeast such as New Jersey, New York, etc.) with California emission standards.

How closely what’s technically legal relates to what’s possible/practical in the real world is a matter of many factors, such as the level of enforcement where you are and what types of special vehicle registrations may be possible. The bottom line is you generally can’t go wrong with a product that has a valid CARB EO and which is being properly used on a vehicle application covered by the EO. Other products may also be fine depending upon your specific situation, but you’ll still have to worry about a technician/inspector getting it wrong even though the product really is OK. Either way, bring documentation.

To help make this more clear, we’ve included some photos of exhaust system parts along with some additional notes related to them. Starting at the cylinder head, it’s generally possible to put some form of header in most cars, especially if they’re older. Shorty and even some mid-length designs are usually fine and many have EO numbers. Long tube designs, on the other hand, are almost never really legal on vehicles that have catalytic converters.

The reason for this is, by design, they move the oxygen sensor(s) further away from the head and allow more heat loss before the converter, thus reducing its efficiency. While it’s not impossible to make a legal long-tube header, it is generally too costly to do so and CARB has very strict requirements for them. Just because a long header has catalytic converters does not mean it’s really legal, especially in California and green states. You may be able to get away with it if enforcement is lax but it’s still illegal.

Only if the header (long, short, or otherwise) makes provisions for all of the required emission controls (oxygen sensors, air tubes, etc.) AND can be shown to not adversely affect the warm-up and function of the OEM catalytic converter does it have the possibility of being legal. If it uses non-OEM cats which have not been exempted and/ordoesn’t make provisions for use of the required sensors (MIL eliminators are NEVER legal for street use on a PCMV), and/or has no EO, it’s not “street legal”, at least not technically.

Mid-pipes and catalytic converters are another area where there is a lot of misunderstanding and misinformation. First of all, it is illegal, under federal law, to use ANYTHING but the OEM catalytic converters as a replacement for at least the first 50,000 miles; in many cases even more. Period. It depends on what emission standards the vehicle was certified to when new as far as the minimum mileage required. Even after you’ve accumulated the needed mileage you may only, technically, use something other than the OEM converter(s) if the original converters get damaged, plugged, or otherwise fail.

Then you can use somebody else’s converter(s), as long as they are properly approved/exempted. Again, just because you have cats doesn’t make them street legal, they have to be the right type of cats for the circumstances. For non-OBDII vehicles (most ’95 model year and earlier) things are not too bad; there are quite a few options for most popular vehicles. For OBDII-compliant vehicles (some ’94s and ’95s plus virtually all ’96 and later model years), however, things are a lot tougher.

Effective January 1, 2009, CARB implemented new regulations for aftermarket catalytic converters, mainly for OBDII-compliant vehicles. To get an EO for such products, manufacturers now have to do much more extensive (and expensive) testing not only for conversion efficiency, but for durability, etc. CARB’s new requirements mandated significantly improved efficiencies with approximately twice the required durability. While still not quite up to levels required for OEMs, this was a challenge for most manufacturers. As a result, there are not nearly as many options available for newer cars as there are for older ones. At least not yet.

In addition to more stringent requirements that basically affected the converter substrate, there was also a requirement to label the converter cans so a technician could readily determine if the converter had an EO or not. This, coupled with significantly increased covert “sting” operations by the regulators, makes it far more likely a technician/inspector will fail you on the visual test if you don’t have truly legal components; even if the vehicle passes the tailpipe emissions test and “blows clean.”

Another requirement in effect from January 1, 2009 is that any replacement exhaust component such as a mid-pipe MUST have the same number of catalytic converters, in basically the same places and of similar size, to the original/OEM component. Previously, manufacturers were allowed to reduce the size/number of converter “cans” by using multiple, smaller substrates in a single can.

This reduced cost, saved weight, and made packaging the converters easier (gave more room for other parts), but it also was usually detrimental to both the efficiency and the durability of the converters. An example would be where ’87-’93 5.0L Mustangs came with an H-pipe with four catalytic converters in four cans from the factory (two up near the OEM manifolds and another two underbody). Most aftermarket H-pipes eliminated the two cans near the manifolds and only had two slightly larger underbody cans that contained two substrates each.

These H-pipes were a lot less expensive and weighed less than the production parts but were also not as likely to pass an emission test, especially as they got older and the emission tests have become more stringent. You may still be able to legally get away with such a set-up in some areas but, for California at least, if you want to buy an H- or crosspipe for one of these Mustangs now you’ll have to get one that has four converter cans like the OEM part. The good news is that the technology and design has improved such that the new parts are not that much more expensive than the old ones, don’t weigh a whole lot more, can actually be easier to install (some come in three pieces instead of one big one), and are far more likely to help your higher-mileage vehicle pass an emission test than the older products.

As far as the cat-back system behind the mid-pipe (or whatever) goes, pretty much anything is fine in terms of emissions, although local vehicle codes and sound laws may determine how much you get hassled. There are a very small number of much older vehicles which used what’s known as a “back pressure EGR” system where a lower restriction/back pressure system could negatively affect emissions. If you have one of these vehicles then you would, technically, have to be more careful about what exhaust components you choose to use. Realistically, however, these vehicles are pretty rare and the likelihood of anyone realizing they are a special situation is minimal. As long as you can pass the tailpipe emissions test and “blow clean enough” it’s highly unlikely you’ll have to worry about failing a visual or function test of the exhaust components you have.

Other than adding a small amount of weight, extra complexity, and taking up more space there usually isn’t much real performance loss on a street-driven vehicle if you leave the emission controls on and then otherwise make improvements and/or compensate for them. Most older emission controls don’t even work under wide open throttle and things like air pumps are mainly used only during cold starts so, again, they don’t really do much other than maybe add a little parasitic drag to the engine.

Things like EGR can actually improve fuel economy under some highway cruise conditions. Newer vehicles have such sophisticated technology (direct injection, variable valve timing/lift, turbos, etc.) that there is almost no perceivable loss in performance on the street and the improvements in fuel efficiency, emissions, and specific power under virtually all conditions far outweigh it.

The vehicle manufacturers have done such a good job using such technologies to meet mandated regulations that many tuners are now deciding to just leave the OEM emission controls on because they don’t really hurt performance and removing them would cause more tuning and other issues.

In the accompanying photos, we’ll show you some of the things to keep in mind if you want/need to have an exhaust system on a PCMV that really is “street legal” in all 50 states, will not cause you to fail a visual inspection (it’s up to you to make sure you pass the tailpipe test), and will still allow significant performance gains. We’ve used a ’91 5.0L Mustang as an example but the same concepts generally apply to virtually any normally registered PCMV with emission controls that’s used on public roads.