They're not all that fancy. My dad's 1967 Volvo 122s had two carbs for a four cylinder engine. It always failed the emissions test and I can't say that it ever purred like a cat.

Hard to imagine a 67 on an emissions test, I'd guess that would be grandfathered.

Many cars for fuel efficiency or performance.

In modern fuel injected cars, secondary intake and fuel injection systems get more complex with rpm; typically its about 3500 rpm or 50% throttle position cause a different fuel map, an intake runner flapper, and for the last 30 years, some automatic cam timing adjustment.

yeah, I'm familiar with the modern fuel injection engines - this conversation was about carburretor engines