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Old 12-04-2009, 11:52 AM   #1 (permalink)
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Acceleration slow or fast? 2003 Chevy Impala

Hi everyone, I just heard about hypermiling a few days ago and thought it would be a fun thing to try. I've read up a bunch, but there's one thing I can't seem to find a good answer about.

Wikipedia says 75-100% throttle is most effecient for acceleration, while multiple other sources say as slow as possible, and a few say inbetween. I read a couple good threads on this forum and different drivers seemed to get different results between different vehicles.

My question:
Does anyone know or have an educated guess for what will work best for a 2003 Chevy Impala? It's a mid-size car with an automatic v6 and no rpm gauge, unfortunately.

Tips on easy effective mods would appreciated as well.

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Old 12-04-2009, 12:00 PM   #2 (permalink)
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Welcome to the site justjohn. Good to see a fellow Wisconsinite.

Slow acceleration is a good general starters tip. If you slowly accelerate you build up less momentum that you may waste by braking during light to light city driving. However, there are more advanced driving techniques.

75-80% is ideal. You want to keep your rpms low, but engine load high. Unfortunately, with an automatic you get one or the other since you can't control engine rpm, just load. Low load means low rpms and vise versa. So, you have to compromise. Usually, moderate acceleration is what I have found to be best. The exact engine load will differ between vehicle as they are designed differently. That is one area where a scangauge would help out.
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Old 12-04-2009, 12:06 PM   #3 (permalink)
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Thanks for the quick reply! I've gotten fairly good at anticipating in just a couple days so (hopefully) that will be somewhat of a non-issue.

As an update, I just found this article which seems to advocate full throttle acceleration, though I haven't finished it yet. Thoughts?
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Old 12-04-2009, 12:10 PM   #4 (permalink)
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If you look at a lot of the bsfc maps (we have a bunch in our wiki), you'll notice an increase in bsfc (bad) at very high loads. This is most likely due to open loop operation of engines where air/fuel ratios are enriched to avoid pinging. That is why the 75-80% load rule came around.
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Old 12-04-2009, 12:21 PM   #5 (permalink)
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Ah, that makes sense I think. Is there an audio cue to tell when you hit open loop?

Also, when you say high load would that equate more with high throttle, high rpm, or something else? (I did notice the drop in eff at high rpm)
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Old 12-04-2009, 12:28 PM   #6 (permalink)
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Some of us use the Scangauge to tell us whether the loop is open or closed.
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Old 12-04-2009, 12:31 PM   #7 (permalink)
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load = throttle basically

As 99metro said, the scangauge is the best way to monitor open/closed loop that I know of. Autospeed does have an article on a "closed loop monitor". I built one a while back and found the scangauge to be much more accurate.
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Old 12-04-2009, 12:40 PM   #8 (permalink)
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Awesome. Thanks for helping me get started!
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Old 12-04-2009, 01:18 PM   #9 (permalink)
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If you can tell what your shift points are, then you've got a good start. My take on it is when you're under 35 or whenever your TCC kicks in, take it easy. Pushing it harder just churns more fluid and is more wasteful. But once your TCC kicks in probably right after it goes into 3rd gear at 35 or so, push it a little harder to get it up to 45-50 and into OD. Just dont push it hard enough to downshift or your gains are lost for the moment.
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Old 12-04-2009, 02:10 PM   #10 (permalink)
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justjohn-

When you're accelerating from a dead stop, remember that the greatest amount of friction occurs when you are starting from a stop. Moderate acceleration from a dead stop is a good way to eat up tires and gas. It's better to take your foot off the brake to allow the car to move forward a little and slowly apply gas until you're in 2nd gear. Remember 1st gear is the least efficient. Once you're in 2nd gear, you can apply a little more gas to achieve your moderate acceleration.

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