The debate is still ongoing and depending on who is interpreting the ruling. See the quote below from the EPA....when you give the government the ability to pick and chose what it enforces we are swirling the drain. I have dealt with the EPA/CARB and there is very little outside the box thinking once rules are written. What about the guy that drives his Miata to and from track days, maybe he has modified his exhaust...He is at the mercy of the EPA to enforce or not enforce the Clean Air Act. What about the guy that has modified his Raptor to do some desert racing....See where I am going with this...this stuff needs to be taken very seriously.
EPA response to Road and Track:
"This clarification does not affect EPA's enforcement authority. It is still illegal to tamper with or defeat the emission control systems of motor vehicles. In the course of selecting cases for enforcement, the EPA has and will continue to consider whether the tampered vehicle is used exclusively for competition. The EPA remains primarily concerned with cases where the tampered vehicle is used on public roads, and more specifically with aftermarket manufacturers who sell devices that defeat emission control systems on vehicles used on public roads."
SEMA's response to Snopes:
Although your article claims that it is “false” that the EPA is banning road-to-race car conversions, the language that the EPA is adding to the regulations (below) literally makes it illegal to make any changes to the “emission control devices” of a “certified motor vehicle” (i.e., any vehicle that was originally sold as complying with emissions standards for street use) even if the vehicle is being converted for racing and will never again be used on public roads. The EPA considers “emission control devices” to include the engine, the computer that runs the engine, the intake and the exhaust, so any changes to these components would be prohibited. The fact that the EPA says that they don't plan on enforcing it does not change the fact that they are adding it to the regulations. SEMA also disagrees with the EPA's position that this was already the law because the Clean Air Act, as written and amended by Congress, was never intended to extend to racing vehicles.
“Certified motor vehicles and motor vehicle engines and their emission control devices must remain in their certified configuration even if they are used solely for competition or if they become nonroad vehicles or engines.” 80 Fed. Reg. 40138, 40565 (July 13, 2015).