"Modern" is a quite vague here. Direct injection (usually coupled with turbocharging) is a key rule of thumb. If your car has a direct injection, turbocharged e

"Modern" is a quite vague here. Direct injection (usually coupled with turbocharging) is a key rule of thumb. If your car has a direct injection, turbocharged engine AND it requires ("recommending" is cheap) high-octane, pay for it. Otherwise, it is probably an overkill.