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Old 06-06-2008, 08:02 AM   #41
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Quote:
Originally Posted by 1993CivicVX View Post
To me the assumption that the fuel savings of DFCO engine on do not outweigh the extra fuel used to make up for the engine braking during the glide.
My own testing and experience have confirmed this for my VW. I suspect it's true for other vehicles too.

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One thing I learned recently is that--at least in my car which is a 5 speed with lean burn--is it's more beneficial to let the revs go a little higher and maintain a gentle foot on the pedal than to be shifting as early as possible and have the pedal near the floor.
It seems that lean burn is better than optimizing for BSFC and reduced pumping losses, and those with cars so equipped maybe should utilize it instead.

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I can only guess that the fuel use is considerably less when 1/4 pressed despite the small difference in power.
Stop guessing. Hook up a meter. The link is in my sig. In my vehicles, at a given RPM, there's barely any difference in fuel usage between 1/4 throttle and WOT at any given RPM. If I'm at 2000rpm with 1/4 throttle, and I go to 1/2 or fullly open throttle, fuel usage barely goes up (except to follow RPM), but power definitely DOES go up.

Oddly, in my VW, 80 or 90% throttle uses MORE fuel than 100%.

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So my hypothesis is that revving to 1500-1800RPM with a low throttle opening instead of always shifting at 1400RPM with the a wider throttle opening is saving me more gas (this flies in the face of Monroe's hypothesis, which I briefly agreed with but am now questioning, that it's better to floor it all the time and be at low RPM as possible.)
Lean burn is the difference.
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Old 06-06-2008, 08:10 AM   #42
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Just read my log. But I only have 3 entries. I have been trying to get the max MPG, but have only started logging my MPG online just recently. I am the slowest guy on the road usually, but I am driving for max MPG. I drive by the Scanguage, and yes it will change the way you drive. You learn so much by it - where the optimal MPG speed is at, how coasting and gliding in neutral saves fuel vice just downshifting or allowing the engine to use compression braking.

It's hard to believe that a device that reads instantaneous MPG readout, along with "current" trip, "today", "previous" and "tank" MPG readouts can actually change the way you drive, but it can. You have to have patience and the willingness to change your habits, as well as the "want" to actually get the best MPG possible.

I am also on ecomodder.com

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Old 06-06-2008, 08:13 AM   #43
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Lean burn is the difference.
As you probably realize, I have lean burn, but what I see is nevertheless very similar to what you described (i.e., with regard to the comparison between light throttle and heavy throttle). So in my view there's still some mystery here, and a need for more testing and data analysis.
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Old 06-06-2008, 08:39 AM   #44
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In my case, it's pretty clear. I've been testing both high and low throttle for accelerating from a stop, over the last several months. No "proper" testing, but daily driving, trying one today and the other tomorrow. All the while, I'm using heavy-throttle P&G once I'm up to speed.

From a stop, lighter throttle is better. Heavy throttle comes into play at higher speeds, in a P&G routine. As I said in another thread, it makes the difference between low 60's mpg for heavy throttle, and upper 60's to low 70's mpg with light throttle.
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Old 06-06-2008, 08:49 AM   #45
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PaleMalenesian: when you say up to speed, how is up to speed?
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Old 06-06-2008, 09:19 AM   #46
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My commute is about 50-50 split with 55 limit and 45 limit. By "up to speed", I mean maybe 40mph in 5th, maybe 45. I use this for the 55-limit segment as well. There are 3 lanes and plenty of room for others to pass. I sometimes go to 40, do a mini-glide to 35, and then PULSE from there to begin my P&G routine.
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Old 06-06-2008, 02:15 PM   #47
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Quote:
Originally Posted by theholycow View Post
Stop guessing. Hook up a meter. The link is in my sig. In my vehicles, at a given RPM, there's barely any difference in fuel usage between 1/4 throttle and WOT at any given RPM. If I'm at 2000rpm with 1/4 throttle, and I go to 1/2 or fullly open throttle, fuel usage barely goes up (except to follow RPM), but power definitely DOES go up.

Lean burn is the difference.
I must be missing something. How can you have more power but "barely use more fuel?"

I know you are using your injector duty cycle gauge ... is the fuel pressure constant or does it vary with throttle angle?

In other words, I could understand small changes in duty cycle contributing to large power changes IF the fuel pressure were also changing accordingly.
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Old 06-06-2008, 04:48 PM   #48
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Well, I was under the impression that fuel ratio pressure is constant.

The thing is, A/F ratio has to remain approximately constant. So, given the same RPM and normal aspiration, it's only going to pull in so much air. As the throttle opens, it doesn't try to get more air; it only gets more air because it's no longer restricted and is pumping more efficiently. The fuel injectors merely follow the amount of air requested.

I may have given the wrong impression. If 1/4 throttle is enough for cruising, 1/2 or 3/4 throttle doesn't throw me back into my seat with my cheeks stretching back behind my head. It just gives me definite acceleration, while usually observing an unexpectedly minor change in injector duty cycle.

Now, the observation that I can't even begin to explain is why WOT actually uses less fuel than 85% throttle while still producing more power. Must be some kind of lean burn. O2 sensor readings aren't as consistent as FI duty cycle readings on this issue, though sometimes they show lean mixture for it. I guess I have to look over the logs more.
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Old 06-06-2008, 05:31 PM   #49
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Generally speaking adding 50% more fuel with throttle at 80& gives you 150% more power.

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Old 06-07-2008, 06:30 AM   #50
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I was just thinking about the WOT remarks and, to me, it makes sense that perhaps at 80% throttle the car is injecting 100% of it's fuel potential, so the injectors are maxed at 80% throttle... WOT would then give you 20% more air to mix that with...? More air = more power, we all know that.

Did I make any sense?
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