From personal experience with several cars, you can apply enough pressure to snap the brake pedal in two and the car will barely slow down. This wasn’t an issue with older cars that had small diameter disks at the front and drums at the rear. The brake pedal would become stiffer but it was still possible to stop the car.
Modern cars have huge brakes that require a massive amount of force. My little Citroen C4 has 308mm rotors at the front. 15-20 years ago you’d find brakes that big only on a Porsche or a Ferrari. The Alfa Romeo Mito, a newer car at about the same size as my Citroen has even bigger brakes: 320mm, with four pot calipers. Try stopping that with no vacuum assist
I have no experience with Citroens, but on every car I’ve owned (admittedly not a huge number) the unboosted brake effort was no big deal - not remotely close to what would be needed to snap a brake pedal. I currently own a full-size Ford van with very substantial brakes: without vacuum boost the pedal force goes from something like 10 pounds to something like 50.
I watched someone deliberately over-rev a 4cyl engine with intent to destroy it and they punched a piston sized hole in the side of the block.
If it were me, I would brake the car down to a manageable speed and slowly turn the ignition key until the engine quit. Keep in mind that by doing this you will definitely load the exhaust system with fuel in a carbureted car (and possibly with a fuel injected car). Restarting it immediately will create an explosion which can blow the muffler apart. I had this happen with an ignition that cut off and then came back on.
This really depends on what vehicle you’re writing about.
My '07 Elantra will let me rev to at least 7000 RPM in such cases, while my '02 Sable would limit RPM to no more than 4000 RPM.
You can run an engine with a 7000 RPM redline like the sable at 4000 RPM for quite some time without inflicting damage.
If you’ve got a diesel, generally there will be a competent rev limiter and this is a non-issue.
Cars made in the last 40 years or so won’t allow you to turn the key to lock unless the shifter is in park. For that matter, part of the purpose of “lock” is to keep the shifter in park.
This is really the opposite of how it works. Larger brake rotors allow you to put more torque on the wheels with a given force. My sport bike has rather large rotors for a motorcycle (obviously without power assist) and if you’re not careful, it’ll throw you over the handlebars. It also keeps the rotors cooler, reducing brake fade. Other things come into play though, such as the weight of the vehicle. When the power brakes started crapping out on my F250, I had to hammer on the brake pedal with both feet to get moderate stopping power.
