If you drive a naturally aspirated car hard for a good 10 minutes (red line every few minutes), is it bad to turn the car off straight away? Should you drive calm for a while, or let it idle for some time? If so, which, and for how long?
There is no need to continue to run a naturally aspirated car after hard driving. Just shut it off an let it cool down. It is suggested you do this with turbocharged vehicles to give the turbo a chance to spin down and cool down which will help with its longevity. There's nothing in a naturally aspirated engine which needs this type of care.
On track, it is typical to take a cool down lap to allow the brakes and drive components to cool down. On the road, I doubt you can get things hot enough to warrant driving a few extra minutes of calm driving however, here is what I do after going out for a spirited drive:
- Turn on to my home street (or whatever destination)
- Turn the heater on (acts as a second radiator fan)
- Coast as much as possible in neutral or use higher gears
- Avoid downshifting/engine braking
- Once parked, if the radiator fan is on, wait for it to cool down enough (with the heater/fan still helping) to switch itself off, and only then turn the engine off.
This is all most likely excessive but helps me feel better after thrashing on my car. Remember that when you shut the engine off, the coolant will circulate as it cools down. Some newer cars even have electric water pumps to continue pumping coolant after the engine is shut off.