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Old 09-09-2008, 08:05 AM   #1
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Air Conditioning, DFCO, and non-DFCO engine braking

I noticed something useful while watching fuel rate in my VW. Of course, using A/C + DFCO during braking is great, since you're otherwise just discarding that energy into friction brakes anyway. What I found, though, is that even when you aren't in DFCO, you can still get some benefit by being in gear at just above idle RPM with your foot off the throttle.

I saw that I was using fuel at the non-A/C rate with my A/C on when I was rolling along in gear at ~900rpm. I wasn't braking at the time, and I was going just fast enough that the car was pushing the engine slightly, rather than the engine at idle speed pushing the car.
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Old 09-09-2008, 01:30 PM   #2
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Thanks. I've thought about that, but never bothered to play with watching the fuel rate on SG that much. I'm always looking for an economical opportunity to run the a/c though. I love my a/c. I guess this is a variation of "A/c only downhill) but with a little wider parameter.

-Jay
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Old 09-10-2008, 09:47 AM   #3
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Doesn't A/C use drop your RPMs by "stealing" engine power, thus DFCO will last a shorter time?

I've actually found sometimes I'd rather be in Neutral than in-gear-non-DFCO because I don't want to stall out and the engine braking isn't allowing me to accelerate down a steep hill. I'd always prefer DFCO mode though, but I shift down 1 or 2 gears in order to induce DFCO when the RPMs are too low.
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Old 09-10-2008, 10:53 AM   #4
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Quote:
Originally Posted by FLAteam View Post
Doesn't A/C use drop your RPMs by "stealing" engine power, thus DFCO will last a shorter time?
My observation was specifically about non-DFCO.

Quote:
I've actually found sometimes I'd rather be in Neutral than in-gear-non-DFCO because I don't want to stall out and the engine braking isn't allowing me to accelerate down a steep hill.
The engine won't stall if you're in gear and going ~60% of idle speed in that gear. Also, if you're interested in building speed then certainly coasting down the hill is better...I was just looking at conditions requiring steady speed or slowing.
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