Why do Cars in the USA produce less visible polluti

[KiltyCol]

Why do cars in the USA produce less visible pollution? In the UK, it is not unusual to follow a vehicle producing visible and smelly (Carcinogenic) exhaust clouds. A quick dash for the ventilation or recirc control to exclude the clouds.
This visible pollution is very unusual in the USA, as they seem to have much stricter exhaust controls on the annual check (MOT type test). Why don't we introduce this here (in the UK), as we are tired of hearing about invisible, odourless, non-carcinogenic CO2 and totally ignoring the cancer causing stink.

[ZiaAries]

In the city I live in, we have to pass an emissions test on all vehicles we own in order to renew that vehicle registration. This is performed once a year. I can't remember seeing or smelling exhaust from a car in a long time. The police would probably pull the driver over if it were happening, but that might not be the case either. Actually, I haven't even thought about such until I read this thread. Maybe that means the emissions testing is working.

If any vehicle doesn't pass the emissions testing, the car must be modified before it can receive license renewal.

[Exodus]

Thats simple, the US has many more pollution laws then most countries. In many states, you are required to pass emission testing, or your plates can be suspended. Many states also have laws where you are not even allowed to alter the emission system or a car, which means no aftermarket mufflers, cat-converters, header, etc.

Most cars that come from over seas, are adjusted for US use in terms of fule-mapping and emissions. For example, the Toyota Supra Twin-Turbo that is made in Japan. In Japan, with their settings, the car is about 290hp. Yet, with the US adjustments and emission settings, the car becomes 320hp.

[Usquanigo]

Thats simple, the US has many more pollution laws then most countries. In many states, you are required to pass emission testing, or your plates can be suspended. Many states also have laws where you are not even allowed to alter the emission system or a car, which means no aftermarket mufflers, cat-converters, header, etc.

Most cars that come from over seas, are adjusted for US use in terms of fule-mapping and emissions. For example, the Toyota Supra Twin-Turbo that is made in Japan. In Japan, with their settings, the car is about 290hp. Yet, with the US adjustments and emission settings, the car becomes 320hp.

US Spec cars have "more power" because the market demands it, and because there is no 'gentlemen's agreement' to keep power down. In Japan everything is UNDER-rated. That may be changing with the new GTR, but for years and years and years, the hotter cars all produced way more than they claimed in the JDM spec.

[Qwynn]

Probably the cars in the UK which have more visible pollution are diesel cars, which are very rare in the US. Diesels tend to run rich on full throttle and produce a lot of smoke.

[KiltyCol]

I've noticed in the UK now that most road fuel stations in the UK have and equal number of regular diesel and regular petrol nozzles / pumps and a often lesser number for Super fuels. On my visits to the USA, there are usually several pumps with 3 grades of gas at each and then the odd diesel pump hidden round the back, although one station had recently changed to 2 grades of gas and one of diesel at every pump. This ties in with your comment Qwynn.