If I rev (for example) a small 1.5L 4 cylinder engine up to 4000 rpm in neutral then let off the accelerator (gas) pedal completely, how much torque will the engine produce as it slows down? How long will it produce that torque? For example if had it in gear and immediately let the clutch out while it was slowing down from 4000 rpm, how much engine force would I transfer to the wheels while the engine was slowing down?
I don't know about modern computer-controlled ignition cars, I guess it depends on their programming, which is adjustable in some cars. some drag racers tamper with the computer.
In the old carburetor cars if you let go of the gas pedal the flow of gas to the carburetor stops and its flap closes. The engine turns into an air pump producing negative torque.
The flow of power reverses, meaning the power from the wheels turns the engine. In diesel trucks, this engine break is used to protect the brakes from overheating.