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Old 04-05-2012, 11:24 AM   #1 (permalink)
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Default Best acceleration technique

My question about the best acceleration technique to use is driven by an article I read in Road & Track at least 30 years ago (but definitely post-Arab Oil Embargo) about some research that BMW had done on the subject.

The result of BMW's test was a somewhat counter-intuitive recommendation: the most efficient way to accelerate an ICE was *not* to adopt a slow, gradual increase up to your cruising speed but, rather, to pretty much "get on it" with a very brisk acceleration (but, they were clear, not wide-open throttle) to get to your cruising speed quickly and then back off. The explanation was that barely part-throttle operation was not efficient at all...and that the "sweet spot" for the efficiency of the ICE under acceleration was an almost-full throttle opening.

So, with that as set-up, what have owners of the first-gen Insight (esp. the hypermilers) found is the case with our car? I should add that I'm not talking about stop-and-go driving, where you're pulling away from a red light and already know that you're going to get caught by the red at the next intersection. This is more along the lines of accelerating from a stop onto a boulevard that's going to run for some miles and allow you to maintain a mileage-friendly speed of something like 45 mph.

Dave
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Old 04-05-2012, 12:06 PM   #2 (permalink)
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I accelerate with alacrity, not WOT or anything like it, usually showing from 3-8 bars on the Assist gauge, then pulse-and-glide forthwith. Seems to work best for my CVT (55.9 LMPG @ 71.5K, AC always on Econ @ 72 setting when warm weather comes, which is 10 months out of the year for us)...
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Old 04-05-2012, 03:55 PM   #3 (permalink)
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While monitoring my OBDII C&C gauge, I shoot for 90% load and go 1st, 2nd, 3rd, then 5th at around 33 mph and let the terrain determine speed from there.
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Old 04-05-2012, 04:47 PM   #4 (permalink)
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Quote:
Originally Posted by xqqqme View Post
the most efficient way to accelerate an ICE was *not* to adopt a slow, gradual increase up to your cruising speed but, rather, to pretty much "get on it" with a very brisk acceleration (but, they were clear, not wide-open throttle) to get to your cruising speed quickly and then back off. The explanation was that barely part-throttle operation was not efficient at all...and that the "sweet spot" for the efficiency of the ICE under acceleration was an almost-full throttle opening.

Dave
I've always believed this and it's worked best for me. My best mileage tanks have come with this style of acceleration and keeping all cruising speeds below 65 mph. Even better if you can stay in the 50's.

I tried it for a whole tank a couple times but "driving like Grandma" never got me any better results. One viable exception is when your are gaining speed on a long downhill grade take as much momentum from gravity as you can get. If the downhill grade is .3-.4 of a mile time it so your at desired speed or even a few mph high when you get to the bottom. Let gravity do the work.

This is an interesting point that has come up once before since I've been visiting the forum.
Thanks - Brian
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Old 04-05-2012, 08:31 PM   #5 (permalink)
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My theory:
Engines are most efficient at "0" in of vacumn.

Install a "vacumn gauge" and use it for accelertaion and obtaining the best mpg.

(Been doing that for years.)

HTh
Willie
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Old 04-05-2012, 09:21 PM   #6 (permalink)
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Do you have a manual or cvt? On my cvt there is a sweet spot on the throttle. If you baby it too much you get no assist and use a lot of gas/take a long time to get up to speed. Just a little more throttle and you get a little assist and the fcd shows about 25 mpg while accelerating. In between these two, difficult to master, you can get about 3 or 4 bars of assist while maintaining 35-40 mpg on the fcd. As a side note I never can do this when the outside temp is under about 60 degrees f, even with the engine warmed up.
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Old 04-06-2012, 01:35 AM   #7 (permalink)
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Personally, I subscribe to the "vertical throttle butterfly" series of methodologies. Sure, it reduces your fuel economy. But it sure as hell is a lot more fun.

I did a test a while back comparing full throttle acceleration to very slow acceleration. It certainly resulted in a MPG benefit, but my average speed dropped by like 10mph and I was glad no drivers behind me owned guns. I wouldn't be able to drive like that all the time.

I got 60mpg zooming around town all day today. Saw redline probably 20-30 times.

I suppose this may seem silly to some, considering it seems that in a lot of discussion I go for maximum MPG. I suppose that should also include maximum MPG while having fun doing it.
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Old 04-06-2012, 09:07 AM   #8 (permalink)
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I like 70% LOD on the C&C gauge, with a slight modification. In first gear, I usually try to start off with no assist and accelerate up to 3000RPM moderately briskly - don't know the LOD. I do this because in my suburban traffic I want to take the most efficient way to a "reasonable" road speed. This phase probably isn't the "best" from a FE viewpoint. Then I try to accelerate in 2nd, 3rd, and 4th at rates just short of assist. I try to use assist as little as possible because I believe the process to be inefficient - I just don't know how much. In my very early days, I was counseled by Rightlandcruiser, a very competitive hypermiler, of this opinion. There is a sweet spot on my car where I can accelerate just short of assist and still pull 60-70% LOD. That is my spot. My FE strategy is to get to lean burn ASAP with a minimum of assist. Traffic conditions mitigate against a fixed plan of course. And, there are always the special situations where the acceleration is downhill or uphill.

There is some crossover point between Granny style acceleration at different LOD and full throttle acceleration, and the point moves around because of the lean burn capability of the car. The Gen 1 isn't like the BMW and early magaine test objects. THEY DIDN'T HAVE LEAN BURN. We have a lot more complicated situation.

On the one hand you have WOT acceleration and high revs, where the power peak resides. On the other hand you have something like 60-70 LOD, partial acceleration with the objective of reaching lean burn in the most effiient way.

In the first case, actually both cases, F=MA (force, mass, acceleration). Mass is fixed so the other two are directly proportional. Hard acceleration = Lots of force and lots of fuel. Through a bunch of conversions acceleration pretty much translates into fuel used. The more acceleration the more fuel - we all pretty much know this, but OTOH one gets to lean burn and cruising speed quicker. With moderate acceleration, say 60% load, one can avoid assist (inefficient) and eventually reach the same lean burn cruising speed.These two approaches both represent some kind of consumption curve and I strongly suspect tha those curves cross at some optimum point - I just know the shape or parameters of the curves.

I propose a test, and maybe I'll do it myself. Find an isolated Level section of road and do two tests.
1. Test one, on level ground, use acceleration of around 60-70%, but always out of assist, to reach 50 mph and lean burn. Reverse direction and repeat the same test over same road section. Average.
2. Test two, on same course, use WOT to get to 50mph, then drive at lean burn 50 mph for the same distance. Reverse direction and repeat. Average.

If I've thought this through carefully, the answer we want is provided by the tests-though the fine resolution of the curve crossover is still not know. More testing at different LOD for test 1 migh find the point.
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Old 04-06-2012, 12:44 PM   #9 (permalink)
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Default Best acceleration technique

Need4Speed, I have a 5M...but we have also owned 2 Priuses (just got our 3rd last week) and I am familiar with the technique when driving a CVT.
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Old 04-06-2012, 11:01 PM   #10 (permalink)
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Quote:
Originally Posted by xqqqme View Post
Need4Speed, I have a 5M...but we have also owned 2 Priuses (just got our 3rd last week) and I am familiar with the technique when driving a CVT.
I know just what you're talking about. With my Prius, there is that fine line between between accelerating and putting the max amount into the pack and keeping from drawing juice from the pack.
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