My friend and I are in and endless debate on whether engine braking wastes gas or not. Anybody have a definative answer for this?

 

So your downshifting to slow you down which in turn raises RPMs, which takes more fuel. My son used to do it just because he liked to hear the engine rev.

 

revving engine = wasting gas

 

Im on the side that thinks it wastes gas..Any physicists here know how this mechanically works?

 

It wastes gas, of course, but it slows the car down, meaning your brakes don't work as hard and will last longer, or so I've heard.

 

Depends. on my car for example (mk3 supra with maft pro piggyback).. when I downshift and decell, my AFR's spike to 22.3, which means it cut the injectors of their fuel. And actually saves me gas compared to throwing it in neutral and letting the car idle as I brake.

 

Here's some simple logic..... Commercial drivers in their 20,000 pound tractor trailers do this. They drive for a living.
The pennies it costs you to downshift is cheaper than brakes.

 

A lot of cars will go "full lean" at 0% throttle

 

the wasting gas is only during the initial point of when you must press on the gas to match engine speed..but while its in gear and your slowing down you are not wasting gas the high rpms is just the engine speed but your foot is not on the gas so therefore it would just be as if you were idling.

 

They use something called a J-brake, where the tractor slows down when they let off the gas.

 

Definitely saves gas.... Mixture goes full lean, and associated EGT drops quickly. Idle circuit then engages around 1200-1400rpm. If you're decelerating in gear from around 2500rpm down to 1800rpm, your injector duty is zero. There is no fuel being used at this point in time. You're also saving brakes, but perhaps creating a touch more clutch wear.

 

yea your brakes will last longer but the clutch wont. id rather replace my brakes any day then have to get another clutch

 

but doesn't down shifting put more wear on the engine as it has to work at higher rpms even if your foot was off the gas pedal?

and if u had a turbo its no good for a turbo either correct?

 

Injectors cycle to "0" (or really close to it) when the throttle is closed.


/thread

 

from what ive been researching.. Engine braking used lil to virtually no fuel at all.. the only reason why the car "revs" up that high is because of the tires spinning and lower gear. also the higher rev sound comes from the cylinders pumping faster. but using lil to less fuel. the car's ecu will cut fuel n yea.. zero fuel usage...

the onlydownside from what ive read is... when revs go up.. more engine wear is present... so its a trade off i guess..

but ive always wondered... what about auto tranny?