dddude55

The engine does not keep stoich on engine braking. Anyone that looks at an a/f gauge while engine braking will see that it will probably read "--" which means the condition is too lean for you wideband to sense. If the engine was maintaining stoich then it would read around 14.7.

You save gas by using the natural force of the engine to slow it down. I downshift all the time, it is a personal choice. It is always good to keep in mind that brake pads will always be cheaper than a transmission.

njsharkracer

you got that post right ddude55. my scangauge reports a 16.3 a/f ratio which must be the upper limit of the narrowband senor our tibs use when the ecu shuts off the injectors.

As for the wearing out your clutch while downshifting, i have no problem doing it quickly. the slight reverse slipping keeps the clutch clean and "deglazed".

dddude55

I just went and took a snapshot of a portion of one of my logging sessions:

Top graph is engine speed(rpm)
Middle graph is narrowband stock primary O2
Bottom graph is tps %



You can see when the rpms gradually drop the o2 sensor bottoms out on it's voltage. That means it is in a lean condition. Now tell me again dtn that the engine tried to maintain stoich

njsharkracer

you know dtn didn't pay attention to the whole scenerio.

what were you doing in that graph? doing 80mph and just coasting down in 5th gear for that big run with the injectors off then downshifting through each gear? that's what it looks like.

HyundaiKitCoupe

it's a kick in the cake if you ask me. to save pad life? you save like .000000003mm's of pad per 4 years, and you waste 4 years of extra stress on your engine. you waste gas, and use the car up more than if you put it in neutral and just coast with the power that you already have made... with traffic patterns, it's not your car that will decide what time you will arrive or how. all that downshifting engine work just to be stuck behind a granny on her phone who isn't turning?

downshifting is used to save pad life in racing like formula 1 where speeds and brake temperatures get extremely high and pads have to be conserved in order to win a race, they reach 16,000 degrees fahrenheit on a single rotor to be exact. in a sh*tbox hyundai commuting to walgreens in traffic to pick up some bayer ultrastrength, you're nowhere near those extremes. haha



why not conserve the engine and transmission life by using neutral as much as possible? all that stoich talk but what about rpm, how would you be saving more gas? pads don't have a single functioning object, they don't get my choice to be saved.

dddude55

Thought I would add the same section of the log but with injector 1:



hkc: engine braking saves gas in the way that if you use your brakes, all that energy your gas put into getting you to that speed is now gone just like that.

njsharkracer

hkc i don't downshift to save pad wear, it's a learned behavior from driving a tractor trailer. the concept is to always be in a gear instead of neutral so you can get back on the gas instantly if a traffic situation comes up that you need to accelerate out of harms way. it takes another half second at least to get the transmission back in gear and the clutch released before you can start hitting the gas again in an emergency.

radu_rd2

ddd, post the injector duty cycle graph too!
edit: nevermind, I didn't saw the second graph, I fail!
It looks like it uses a tiny bit more fuel at higher rpm, but still very little

HyundaiKitCoupe

ah sure in that case yes i agree if you see cars accelerating in front then yes it would be proper. the other thing is if you coast into a 90 degree turn, why not just coast, and then throw it in the best lowest possible gear? i noticed that if i'm turning a right angle and leave it in gear then the car hops around back and fourth before and after accelerating with that loosened throttle. i've decided that it can't be good for the transmission.

does that "getting back the power" really make so much of a difference? i'd say it's no more than 1-2k rpm difference of recovery.

that makes sense.

Stocker

I'm a big fan of not rebuilding engines prematurely due to higher than necessary operating speeds. Put it in neutral and use the brakes. Brakes are cheap and easy. Rings are not.

On the other hand, these engines are known to last several hundred thousands of miles before 1st overhaul, so drive how you want!