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Old 03-01-2009, 09:23 PM   #1
marx404
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Default 2500 - the magic number

I am still playing around on my 45 min drive to work every day, seeing how I can optimize mpg while not driving like an old granny. I have an automatic so this would apply differently to sticks, I am sure.

I noticed first of all the idle speed seems to be 8K rpm, checked a few Astras found this to be true. At just under 60 mph my rpm is at 2500 rpm. Using my Instant Fuel Mileage on the BCM it says I am getting at or above 30 mpg. When I go above 60mph, I am higher than 2500 rpm and my mpg is sequentially lowered.

So, from this I have deducted that easy on the throttle from 0-30 mph, then step on it (not floor it) till 60mph and I can maintain a healthy average of 30 mpg and still have fun on my way daily drive! 2500 is the magic number for my automatic.

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Old 03-01-2009, 11:32 PM   #2
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Default Re: 2500 - the magic number

Quote:
Originally Posted by marx404 View Post
I noticed first of all the idle speed seems to be 8K rpm, checked a few Astras found this to be true.
.


8000 rpm idle seems rather high. you might want to get that checked out. maybe it's just an automatic thing though.

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Old 03-01-2009, 11:41 PM   #3
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Default Re: 2500 - the magic number

Quote:
Originally Posted by mdcclxxvi View Post
8000 rpm idle seems rather high. you might want to get that checked out. maybe it's just an automatic thing though.
lol, im guessing he means 800.

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Old 03-02-2009, 12:43 AM   #4
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Default Re: 2500 - the magic number

yes, I meant 800. my bad, one too many zeros.

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Old 03-02-2009, 03:58 PM   #5
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Default Re: 2500 - the magic number

At 8k, putting the car into drive would be wild.

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Old 03-02-2009, 08:28 PM   #6
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Default Re: 2500 - the magic number

Quote:
Originally Posted by marx404 View Post
I am still playing around on my 45 min drive to work every day, seeing how I can optimize mpg while not driving like an old granny. I have an automatic so this would apply differently to sticks, I am sure.

I noticed first of all the idle speed seems to be 8K rpm, checked a few Astras found this to be true. At just under 60 mph my rpm is at 2500 rpm. Using my Instant Fuel Mileage on the BCM it says I am getting at or above 30 mpg. When I go above 60mph, I am higher than 2500 rpm and my mpg is sequentially lowered.

So, from this I have deducted that easy on the throttle from 0-30 mph, then step on it (not floor it) till 60mph and I can maintain a healthy average of 30 mpg and still have fun on my way daily drive! 2500 is the magic number for my automatic.
The auto trans on the astra, or at least as I have noticed with my driving, rarely rev at higher than 2500 rpm anyways. Most Ive noticedit is around the 3000's range but is usually consistantly in the mid 2000's. You are right tho the mid 2000's range seems to be the best on fuel consumption, I have noticed this myself. Starting easy on throttle is the way to go, since your not guzzling gas with a heavy foot, and the gears move early in, rather than a heavy foot, wasted consumption and no benefit

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Old 03-02-2009, 09:27 PM   #7
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Default Re: 2500 - the magic number

this goes for every car, 2500 is the magic number for most cars out there.

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Old 03-02-2009, 10:12 PM   #8
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Default Re: 2500 - the magic number

Quote:
Originally Posted by marx404 View Post
I am still playing around on my 45 min drive to work every day, seeing how I can optimize mpg while not driving like an old granny. I have an automatic so this would apply differently to sticks, I am sure.

I noticed first of all the idle speed seems to be 8K rpm, checked a few Astras found this to be true. At just under 60 mph my rpm is at 2500 rpm. Using my Instant Fuel Mileage on the BCM it says I am getting at or above 30 mpg. When I go above 60mph, I am higher than 2500 rpm and my mpg is sequentially lowered.

So, from this I have deducted that easy on the throttle from 0-30 mph, then step on it (not floor it) till 60mph and I can maintain a healthy average of 30 mpg and still have fun on my way daily drive! 2500 is the magic number for my automatic.
An engine going at higher RPMs is consuming more gas, it just appears to be higher at 2500 in particular because you are checking at cruising speed (which happens to be when the Astra reaches that point) and at such speed, there is no higher speed to go into that would further reduce the RPMs. Plus, at highway speeds, the faster you drive, the more the engine will drink, due to having to fight increasing air drag (which is exponential with speed, meaning going 10% faster means 21% more air drag). If you could go into a higher speed that would make the engine turn at 2000 RPMs at 60 MPH, you'd get even better fuel economy, at the expense of acceleration, that is (in part) what they did with the Cobalt XFE to get class-leading fuel economy. That's also why the Impala, built to be a highway cruiser, turns at about 1500 RPM at 60 MPH, so that even with a relatively old V6, its highway fuel economy would be pretty good.

I have a manual ION and an aftermarket tool to show instantaneous gas mileage, I'm very aware of the importance of RPMs in fuel economy. With an automatic, since the car decides by itself what speed to select, your control is limited, but here's what I have observed:

-If you kick down on the gas pedal, the car will usually downshift (increasing RPMs), even if you let it go a bit, it's going to hold on to that gear for a bit more (to avoid seeking gears).
-If you let go off the gas pedal for a second, the car will go into the highest gear its programming will allow it to go at that speed, if you start back on the pedal slowly, it will keep into that gear until you demand too much out of it and it will downshift.

Consider the gas pedal in an automatic as if you're "demanding" power to the car, as the gas pedal is in fact deciding not only how much gas to let through the throttle, but what gear you are going to be into. If you want to help your fuel economy, you'll have to be watching your RPMs and try to ask indirectly the car to upshift a bit sooner by carefully choosing the pressure to put on the gas pedal.

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Old 03-02-2009, 10:48 PM   #9
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Default Re: 2500 - the magic number

Quote:
Originally Posted by Sival View Post

-If you kick down on the gas pedal, the car will usually downshift (increasing RPMs), even if you let it go a bit, it's going to hold on to that gear for a bit more (to avoid seeking gears).
-If you let go off the gas pedal for a second, the car will go into the highest gear its programming will allow it to go at that speed, if you start back on the pedal slowly, it will keep into that gear until you demand too much out of it and it will downshift.

Consider the gas pedal in an automatic as if you're "demanding" power to the car, as the gas pedal is in fact deciding not only how much gas to let through the throttle, but what gear you are going to be into. If you want to help your fuel economy, you'll have to be watching your RPMs and try to ask indirectly the car to upshift a bit sooner by carefully choosing the pressure to put on the gas pedal.
good way to put it(Y)

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Old 03-03-2009, 06:12 AM   #10
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Default Re: 2500 - the magic number

By the time I reach 2500 things start get really interesting and very uneconomical

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Old 03-03-2009, 11:20 AM   #11
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Default Re: 2500 - the magic number

Once warmed up, I shift at 3000 - 4000 and follow the advice from a friend many years ago, about driving a standard:
"Always be in a gear you can accelerate in."

I like to be around 3000 rpm and mostly use 3rd and 4th as top gear around city streets.
Only when I get on an arterial highway where they have at least an 80Km/Hr speed limit, do I use 5th.

You can drive a 1.8 16-valve at 4000 RPM until hell freezes over, it's not a tractor for god's sake.

I realize this is not the optimum gas-mileage way to drive, but it seems to match the performance of the car/engine, which is more important to me than mileage.

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Old 03-03-2009, 11:27 AM   #12
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Default Re: 2500 - the magic number

I can get an instantaneous mpg of less than 10 at 2,500 in D4 (under moderate but not WOT acceleration) so I don't see any particular "magic" about that rpm taken alone as a single data point. There are some good mpg increasing tips in this thread but it also has a lot of evidence by implication that these cars need at least one more ratio in the automatic transmission to optimize high speed cruising mpg. By high speed cruising I mean neo-legal (won't get a ticket) speeds on great plains Interstate Highways (80 mph or a little over). To say you will get the best mileage if you stay at or under 2,500 is also to say stay at or under XX mph. I can probably get the best mileage in D4 at the "magic" speed of about 38- 42 mph but on the Interstate it would be illegal and I would get a lot of horns and fingers! ;>)

I just don't see how a car from a German company doesn't have a gear for efficient cruising at or around (or just over) 80 mph. But then I do realize we are hamstrung by the one engine with only two possible transmissions and the Opel and Vauxhall's do have more options -- we just don't.

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Old 03-03-2009, 12:39 PM   #13
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Default Re: 2500 - the magic number

Quote:
Originally Posted by Sival View Post
If you want to help your fuel economy, you'll have to be watching your RPMs and try to ask indirectly the car to upshift a bit sooner by carefully choosing the pressure to put on the gas pedal.
Simple and very well put. And although the automatic tranny has shortcomings, this alone I find can overcome some of them.

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Old 03-03-2009, 01:30 PM   #14
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Default Re: 2500 - the magic number

Quote:
Originally Posted by BNM449 View Post
Once warmed up, I shift at 3000 - 4000 and follow the advice from a friend many years ago, about driving a standard:
"Always be in a gear you can accelerate in."

I like to be around 3000 rpm and mostly use 3rd and 4th as top gear around city streets.
Only when I get on an arterial highway where they have at least an 80Km/Hr speed limit, do I use 5th.

You can drive a 1.8 16-valve at 4000 RPM until hell freezes over, it's not a tractor for god's sake.

I realize this is not the optimum gas-mileage way to drive, but it seems to match the performance of the car/engine, which is more important to me than mileage.

~N~
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Old 03-03-2009, 01:46 PM   #15
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Default Re: 2500 - the magic number

Quote:
Originally Posted by BNM449 View Post
Once warmed up, I shift at 3000 - 4000 and follow the advice from a friend many years ago, about driving a standard:
"Always be in a gear you can accelerate in."

I like to be around 3000 rpm and mostly use 3rd and 4th as top gear around city streets.
Only when I get on an arterial highway where they have at least an 80Km/Hr speed limit, do I use 5th.

You can drive a 1.8 16-valve at 4000 RPM until hell freezes over, it's not a tractor for god's sake.

I realize this is not the optimum gas-mileage way to drive, but it seems to match the performance of the car/engine, which is more important to me than mileage.

~N~
I'm curious what kind of mileage you're getting with that driving style.

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Old 03-03-2009, 01:50 PM   #16
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Default Re: 2500 - the magic number

thats how i drive ( 5 speeds) and i have 8.3 liters by 100km(around 30 mpg)for 10 000km (7500 miles)

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Old 03-03-2009, 01:59 PM   #17
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Default Re: 2500 - the magic number

http://www.metric-conversions.org/vo...id-gallons.htm

http://www.metric-conversions.org/le...s-to-miles.htm

...but than again as dangerd points out, he has a stick. Sticks will typically get better mileage than an automatic.

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Last edited by marx404; 03-03-2009 at 02:06 PM..

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Old 03-03-2009, 02:11 PM   #18
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Default Re: 2500 - the magic number

If I drive aggressively I get around 27 mpg and that's without using A/C. When I drive to conserve fuel I'm getting 30+ in the same situations.

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Old 03-04-2009, 12:17 PM   #19
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Default Re: 2500 - the magic number

"I'm curious what kind of mileage you're getting with that driving style."

Robor7:

When the car was new last August I started at well over 10 L/100km, as the car broke in I got down to 8.8 L/100Km.

Now with winter ( slippage) and the winter tires, it's back up to dead-on 9L/100Km.

I expect when spring/summer kicks in and I put the original tires back on, I'll get back down to the mid-to-high 8's.

There is another factor too: when my car is loaded down with my band equipment or pellets for my stove, I drive more conservatively but the load's weight affects my average fuel consumption.

~N~

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Old 03-04-2009, 12:40 PM   #20
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Default Re: 2500 - the magic number

Quote:
Originally Posted by Germane German View Post
I can get an instantaneous mpg of less than 10 at 2,500 in D4 (under moderate but not WOT acceleration) so I don't see any particular "magic" about that rpm taken alone as a single data point.
The transmission doesn't lock up the torque converter during acceleration. FWIW, acceleration in any gear is a pig on gas.

For optimal fuel economy (w/ an auto), you want to be in 4th gear, with the torque converter locked up, and going as slowly as possible at a constant speed.

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