Back in the old days when cars were equipped with drum brakes, cars had very long stopping distances. It was therefore typical for drivers to shift into a lower gear, ease out the clutch, and use the internal friction of the engine to help decelerate the car. That’s no longer necessary today because disc brakes are incredibly powerful. The change to disc brakes not only shortened stopping distances, but according to Kevin Clemens in “Motor Oil for a Car Guy’s Soul”, disc brakes are the reason why people now drive with so little respect for each other.
Despite the demise of drum-brakes, engine-braking is still useful today. When going down a long descent, using some engine-braking prevents your brakes from overheating. Also, if your car is relatively new, it probably has DFC (deceleration fuel cut-off) which stops fuel going to your injectors if you are decelerating in gear. So engine-braking can save you gas.
Unlike the street, there is really no use for engine-braking on track. Your brakes should be set up so that the fronts start sliding just before the rears. If you add engine-braking to a FWD car, your braking distance will become longer and braking in a corner will see you understeering off track. If you add engine-braking to a RWD car, your stopping distance is longer and you can spin even when braking in a straight line.
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