They do ron ron ron they do ron ron

I'm bored lol

Actually, in case the youngsters reading this don't know what the difference is between 2,3,4,5 star petrol - it was the octane level which I think it was largely the amount of lead in it. What star petrol you needed was mostly down to the compression  ratio of your engine. The lower the star, the less lead and hence the easier the engine would suffer from pinking (or I think it's called pinging if you are in USA). Pinking is where the fuel/air mixture ignites too quickly and can cause damage to engine over time. The lead slows down the burning of the fuel/air mixture (we are only talking very small fractions of a second). The lead also lubricated the valves.  Hence cars that were designed before unleaded petrol came along did suffer from using unleaded petrol. eg. The Mk2 Fiesta 1.1L I had at the time. It was horrendous on unleaded. The ignition timing had to be retarded (yes youngsters you could adjust your ignition timing by undoing a bolt and turning the distributor round) to stop them pinking but that reduced power and acceleration. And then valves would suffer over time as no lead to lubricate them. 

Hope I got that right but I am sure there are other oldies on here who will say if I got the technical bits wrong. And there may be no youngsters reading this who care anyway. 

4 minutes ago, isetta said:

 

Hope I got that right but I am sure there are other oldies on here who will say if I got the technical bits wrong. And there may be no youngsters reading this who care anyway. 

Seems a fair summary to me😀. By the time unleaded came in, a lot of cars were already being manufactured with hardened valve seats, so no problem there with the lack of lead. The issue in a lot of cases was that the unleaded came in just one grade, equivalent to 3 star, which caused problems if you had something that needed better stuff. My Vauxhall at the time had a little plug in the wiring loom which you had to remove, then replace in its socket the other way round to use unleaded. Effectively it just knocked the ignition back a few degrees, but the driveability was ruined. So I stuck with the leaded until I went diesel.