when you downshift in order to slow down, do you burn more gas to make the engine rev higher?

Answer 1

By using the engine to brake, you'll burn more gas and put additional wear on "hard parts" of the engine and transmission (that is, parts not designed to wear out and be replaced easily). Each individual instance is not particularly important, but cumulatively (over time) it'll add up to quite a lot of gas, and quite a lot of wear.

Use engine braking to slow the car under the following conditions:

1. You're already near the top of the engine speed range in a particular gear, and will be slowing down briefly before speeding back up again, or holding the slower speed in the same gear -- in this case, lift off the gas and let the engine do the braking.

2. You're going downhill, and so need to use engine braking to keep the car at a constant speed without using the brakes (so that they don't overheat.)

3. In an emergency, along with the parking brake, if you suddenly find the hydraulic brakes in your car have stopped working.

In all other instances, you're better off adjusting your speed with the brake. Your car's brakes are designed to slow the car, and they're a "wear" item; disposable, cheap to replace, and made to withstand the abuse of slowing the car from speed over and over and over.

A lot of people have been taught to use engine braking to avoid wearing out the brakes, but that's a lot like sitting on the arm of a chair to avoid wearing out the seat cushion; all you'll end up with is a worn arm that's a lot more expensive to repair than the cushion. Similarly, some people think they're "saving" the brakes by engine braking on a regular basis, but they're really just setting themselves up for premature "hard part" repairs -- a far more expensive proposition.

So, in short, use engine braking for downhill runs to keep the brakes from overheating, and when adjusting your speed downwards without changing gears -- but that's about it.

Unless you're racing, of course, which is a whole different proposition (and one that I assume doesn't have relevance here.)

Answer 2

A fuel injected car won't burn any more gas than if you used only the break. The key here is that engines last longer than break pads and gas is considerably cheaper more convenient than taking your car to the shop for new brakes. I'm not saying that you will be going through break pads every other day but to strictly answer you question the gas you are burning over the life of your car is about the same as the gas you will need to drive to the auto shop to get your over worked brakes overhauled.

Answer 3

Fuel injected cars don't suffer this strain 'cause they adapt to this abnormal function quickly-less than 1/8th of a second. The real gain here is in driver control of speed and the consequent attitude of interfearence.Control involves driver confidence and speculation. Poor judgement or inexperience is no substitute for a qualified driver. Qualifications must include overcoming previous inefficientcies in an instructial way.Experience will prevail.

Answer 4

No , The engine will just burn more of the unburnt fuel that normally escapes out the exhaust cycle.

Answer 5

Yes by using the engine as a brake you will use more fuel

Answer 6

Not really (not enough that you would really notice anyway).. the throttle is in the closed position.. you are using mainly air for compression breaking...