Is it legal to remove emissions equipment from old cars?

I know laws vary by state, and that there are federal laws.

My '66 MGB does not have smog equipment, and the engine puts out 95 horsepower (book value). By the time the last MGBs rolled out of Abingdon in 1980, the smog pump and other emissions controls only left (IIRC) 67 horsepower to drive the car. A Facebook group I’m in shows people who remove their emissions control equipment from their later-model cars.

ISTR in California that cars of a certain age were exempt from smog testing. (This was a long time ago, so it may have changed.) Given that there aren’t that many 40- to 50-year-old cars on the roads, is it, generally speaking legal to remove smog equipment?

Smog requirements are: California is 1975 or older. Washington is 25 years (so 1993).

Yes, they vary by the state.

But also consider this: in 1966, published official horsepower figures were SAE gross numbers. In 1971 and forward, the horsepower was SAE net HP. This accounts for a lot of the “loss” of power too. I dare say the actual net rating of the 1966 car was closer to the high 70s. With the 1980 car with an A.I.R. pump and catalytic converter does rob power, no doubt, and I’d do the same, but really wouldn’t expect a night and day difference, as the smog era engine is likely saddled with milder camshaft timing and more restrictive head design in deference to lower emissions.

Yes, I’ve heard the engines were ‘de-tuned’. If I had a 1980 MGB I’d put in a cross-flow alloy cylinder head, Weber carburettor, manifold, etc., and a ‘fast road’ camshaft.

But I don’t have one and I’m not getting one. The performance parts, and MGB people talking about removing emissions equipment, inspired the general question though.

I vaguely recall having a discussion with someone at EPA who became quite excited about “tampering with an emitting device”, so it may not just be state rules.

I’m old enough to remember when emissions control was added to cars. Removing that stuff was a profitable side line business for mechanics.

It didn’t last long. The increased performance didn’t justify the expense. The car was considered illegal and warranty voided. Getting any service at a dealership was problematic.

People accepted emission control within a few years. I don’t think a modern car will run without it.

I’ve wondered how many vintage cars get sold with the emission control missing? There must be a few survivors out there that got modified.

As I understand it, the Federal law in question here is the Federal Clean Air Act. While many states do not actually test emissions on cars older than a certain age (typically 25 years), it is illegal under the Clean Air Act to remove the pollution controls on cars that were manufactured with them in place.

If you have an antique car that is exempt from emissions inspections (I have a 74 Super Beetle, for example), the chances of you ever getting caught are pretty darn slim, but it’s still technically illegal.

This might just be rumors, but I have heard that federal inspectors will sometimes go to old car shows to look for people violating the law. Some folks who want to remove their catalytic converter will replace it with an empty shell instead of a straight piece of pipe just so that anyone doing a quick visual inspection won’t notice anything wrong. Again, technically illegal, even if you do have almost no chance of getting caught.

Many also don’t test many newer cars on the road. Of the three states I’ve registered cars in none have statewide testing requirements. Ohio and Indiana test in a limited number of counties, 7 and 2 respectively. Michigan has no emissions testing. I have never had a car tested.

Marijuana is also against federal law but there are a number of states where that’s not much of a limitation.

I suspect that if they ever did this they stopped decades ago. If you go to any car show featuring 1960 and 70s muscle cars you have zero chance of finding any emissions equipment. They could ticket the entire show. Except for someone with a “survivor” car. In those classes the originality of every single part is counted. People will carefully cut open a muffler and replace the stuffing so it sounds good, and reweld it to avoid changing out the muffler. An original muffler from an old Ferrari might be worth $10,000.

Plus, classic cars can usually get special plates in most states. This limits their driving to occasional use such as car shows. Perhaps this category of car is excluding from an emission laws anyway?


One possible workaround is to get an Antique Automobile registration, then go ahead and yoink the smog crap.

My understanding is that this doesn’t exclude you from the emissions laws. Obviously a Model T can’t be expected to pass a modern emissions test, but if your antique car had a catalytic converter it is technically illegal for you to remove it. The vehicle has to be equipped with whatever emissions it was built with.

Pennsylvania (where I live) has Classic plates and Antique plates. Classic plates are for vehicles more than 15 years old, and they have to have a yearly safety inspection, but they do not need a yearly emissions inspection (PA requires yearly safety and emissions inspections for all regular vehicles). Antique plates are for vehicles more than 25 years old, and antique vehicles do not need a safety inspection or an emissions inspection.

I bought my 74 Super Beetle several years ago. For as long as I have owned it, it has never been inspected by the state in any way, shape, or form. There are rules about how many miles I can drive it in a year, but no one has ever checked its mileage. The car is supposed to be “substantially as manufactured”, but no one has ever checked that either. Old Beetles don’t really have anything in the way of emissions controls on them, so it’s not an issue for me, but technically, if an antique car in PA was made with emissions controls on it, it’s illegal to remove them. From a practical point of view, I could do pretty much anything I want to this or any other antique vehicle and no one from the state or federal government would ever know anything about it.

I suspect that very few Classic and Antique vehicles in PA still have all of their emissions equipment installed.

Incidentally, PA’s emissions inspection is that they plug an OBD-II scanner into it and let that decide if it passes. If the vehicle is older than OBD-II was required (1997, I think) then all they do is a “visual inspection” where basically all they do is look underneath to make sure you haven’t ripped off the catalytic converter. It’s all of 30 seconds or so of work either way, and for that they ream you for $45, most of which goes to the state, not the mechanic.

Right. 42 USC 7522(b).

The fines can be thousands of dollars.

This sounds like a ghost story old men tell around the campfire. Look over this list of CAA violations related to engines.

The violators are overwhelmingly importers, manufacturers, or shops that removed emissions equipment. I don’t see any fines for individuals that modified their own cars. I’m guessing that individuals are not an enforcement priority for the EPA.

Even if you owned a car that had its emissions controls removed, the EPA would have to prove you removed it or conspired to remove it (e.g. by paying a shop to remove it). States could fine people who operate cars on public roads without emissions equipment but it’s much easier to catch those cars with annual inspections if states really care. Many states don’t inspect older cars for emissions.

It’s illegal and the EPA will go after shops that do this.

Tons. I’ll bet that many '70s and early '80s models with finicky emissions equipment like air pumps and computer controlled carbs are more likely to be sold today without that equipment than with it. Once it’s gone, few owners will put it back. California is probably the exception because they do annual emissions inspections on even these old models and they visually look for the equipment even if the car passes the emissions test. In other states, it’s easier to get away with driving a car that is not in compliance.

IANAL, but I don’t see anything in the law cited that would make such modification illegal for the ultimate purchaser to perform. Everything there is about modifications made prior to a final sale. So, as long as you never sell the vehicle I don’t see how that law would apply to you.

Of course, if would not surprise me if the resulting vehicle would be illegal to operate on public roads in many states, but that’s beyond the scope of the OP’s question.

I got my citation wrong. It’s paragraph (a)(3)(A), which says it’s illegal:

A 1980 MGB has lowered compression and a single Stromburg Carb and may have a bit of detuned spark advance.
That is the HP loss.
The air injector pump, unless the bearings are seizing, takes nothing appreciable to turn, and the catalyst used on them is just the bare minimum to make the EPA happy, it does not restrict much (nor do much either)

You would not gain anything from de-smogging it really.

The 1980 MGB is also carrying around probably 100 or more extra pounds in those
crash safety big rubber covered steel bumpers.

On cars with a catalytic converter the exhaust can be unbolted from the exhaust manifold and the canister for the cat can be removed, then put the exhaust back together. This is called ‘gutting the cat’. But now you will begin to get error codes set by your car’s PCM due to the new readings from your O2 sensors. So you replace the O2 sensors with O2 simulators. The simulators will tell the PCM that everything is fine, all of the time, even when it s not, and will never set a code. Some error codes may need to be tuned out by some simple reprogramming.

Of course this is illegal but there is really no way for a DEQ inspection to find this unless your car is running crappy. Many DEQ sites have now gone to reading your engine codes via OBD II and a visual inspection, neither will find this. Clearing your error codes before going in for a test doesn’t work because the engine has to go through several cycles to reset the sensors, so DEQ can tell if you have cleared them before you came in to test. Fool the PCM, no codes, no issue. These tests are really not so much at test as just seeing if your car is in good shape.

Sure, a modern car can be made to run without it. This is what aftermarket tuners do in an effort to get more power out of the engine. For gasoline engines, it may go as far as installing an aftermarket ECU that ignores the usual OBD2 diagnostic sensors and allows the user to input custom fuel, ignition, and/or turbo boost maps.

A popular mod among diesel truck owners is the “DPF delete kit,” which facilitates the removal of the diesel particulate filter (which keeps the tailpipe from releasing soot into the environment). Some folks think it robs them of power/economy, or will clog over time or will damage the engine. Things like this are typically labeled “FOR OFFROAD USE ONLY,” which may or may not offer legal protection to the retail seller, even when the vehicle gets used on-road.