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Old 05-19-2010, 11:34 PM   #1 (permalink)
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Accelrate tech-1/4 throttle vs 3/4 = same result

I should start by asking how accurate is a scan gauge on on very short distances? (under 1 mile)

My theory is that the faster you can get to 40 (desired speed to maintain) the sooner you will be in the optimal gear for cruising most efficiently. This only works out if you can maintain the cruising speed for at least 1/4 mile.

I know it sounds backwards, I always assumed you should accelerate as slow as possible, but the readings I've been getting from the scan gauge are saying otherwise. Scan gauges don't lie, or do they?

This is based on an 01 automatic corolla

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Old 05-20-2010, 03:05 AM   #2 (permalink)
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Quote:
Originally Posted by Rockstock View Post
I know it sounds backwards, I always assumed you should accelerate as slow as possible, but the readings I've been getting from the scan gauge are saying otherwise.
You are right on with getting to speed ASAP. The rule here is accelerating with 70%-80% throttle. Of course, if your criusing distance will only be 1/4 mile, or any other short distance (stop sign, red light, etc.), then it's better to accelerate to a lower speed and then coast. The extra 1-2 seconds it takes to get there are well worth the fuel saved, especially if you have to slow down or stop anyway.
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Scan gauges don't lie, or do they?
Only people lie. But a SGII may not tell the whole truth. Make sure it's calibrated, verify it with a few tanks, and everything should be OK.
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Old 05-20-2010, 06:39 AM   #3 (permalink)
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This is true. More throttle generally puts the engine in a more efficient portion of its load curve, so it takes less fuel to get the same total work output, just over a shorter period of time. Of course, with an automatic, there's a point above which gassing it harder only makes it shift way too late, bringing FE back down. The challenge is finding the sweet spot. With a stick, you can run 70% throttle and still shift early, giving more benefit from this.
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Old 05-20-2010, 07:24 AM   #4 (permalink)
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Best efficiency will be at just below 0 manifold vacuum, without enough throttle application to cause full load enrichment. This can be at 25% throttle position, so I like to use manifold vacuum instead of throttle position, since it is a much more precise measurement of actual load on the engine. Engine load can change dramatically with grade changes, without any difference in throttle position.

In my VX, if manifold vacuum is above 6 inches, then lean burn is working, which can reduce the fuel component of the air fuel mixture from 14.6 to 1 to 22+ to 1. This may make it more effective for me to accelerate in lean burn since my consumption is reduced by close to 33% if I can use the lean burn on acceleration.

In normal non lean burn engines the 70-80% throttle position is probably your best bet for acceleration, but if your manifold vacuum is below 2 inches and your throttle position is not high enough to bring on full load enrichment then it really is not much of a difference.

If you are using higher gears for your acceleration, increasing the throttle position beyond a certain point may not give you an increase in acceleration unless you downshift. That is where the choice becomes potentially significant. Longer in the higher gear at the same load, or shorter in the lower gear at the same load. If the time in the higher gear is a lot longer than the time in the lower gear then the lower gear would be better. As the difference in time between the two gears becomes less then the benefits of shorter pulse to speed versus increased consumption during that pulse will switch from the lower gear choice to the higher gear choice.

Not sure if that explanation makes any sense .

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Old 05-20-2010, 08:40 AM   #5 (permalink)
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What about getting back up to cruising speed after slowing down if you're still in top gear? Like maybe from 30 to 50 MPH.
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Old 05-20-2010, 09:57 AM   #6 (permalink)
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Use about 3/4 throttle in 5th gear. If it's too low at 30, you might start in 4th and shift somewhere along the way.

With the rpm that low, you're not accelerating like crazy. What you're doing is opening the throttle valve so the engine can breathe its best.

Autospeed - BSFC article

The Scangauge will be correct, up to the point where the ECU goes into Open Loop. If you press the gas pedal too much, it ignores the exhaust oxygen sensor and just dumps extra fuel in to avoid a lean mix. The Scangauge has no way of knowing how much extra fuel, since it's not reported to the OBD system. As long as you avoid full-throttle open loop, it'll be accurate.
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Last edited by PaleMelanesian; 05-21-2010 at 08:52 AM..
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Old 05-23-2010, 12:13 AM   #7 (permalink)
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Each car is different, however the only time heavier acceleration may have no
ill effect is when one plans to cruise for a long period of time, such as entering
an Interstate.

I just don't foresee it in local traffic, all it takes is that next traffic light to turn yellow...
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Old 05-23-2010, 05:07 PM   #8 (permalink)
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In traffic, you have to accelerate a little slower, but you just get off the gas at a lower speed.
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Old 05-28-2010, 08:28 PM   #9 (permalink)
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and when you are at 60 kmh , and youre in 5th gear . is it better to downshift to 4th gear if you go uphill or the 5th gear is good ( in my commute , I can do it in 5th without WOT )

what is most efficient?
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Old 06-02-2010, 10:37 AM   #10 (permalink)
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Lower rpm is better. 5th gear is better, until the point where you cannot maintain the speed needed.

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