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85 mph puts it at 2400 rpm in 6th gear, or 3100 in 5th.
 

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Hmm. Good to know, I think I've reached that speed twice in 2 years do never got time to look
 

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Yay math!
 

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I just bought a 2005 LS 4 door automatic with 31k miles from the estate of a lady that passed away. I checked the "information center" and it indicated that she was averaging 33.8 mpg. Not sure about her driving habits.
 

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i get 30 on the highway, i am a lead foot though, its almost always to the floor lol. only thing that slightly helps is the new K&N filter i put in recently. i want to get a CAI for it.
 

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Im getting 21mpg out of my 09 SS/TC sedan but I usually find myself in a quick race atleast once every full tank lol I drive about 10 miles thru the city to get to the highway and then it's 27 miles to work on the highway.
I don't get on it otherwise, I cruise at 75-80 on the highway and 40- 55 thru city. I feel as if that is rather low for my MPG.
 

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21 is a pretty poor number for an LNF, but it's understandable since you're more or less expected to get on it every so often lol. If you can short shift and cruise at 55 (harder than it sounds), you'll be golden.

My Eclipse averages about that much, that's with a truck engine (3.8 MIVEC) and the weight of a small moon to drag around lol
 

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When I left today I looked at the avg mpg and it is saying 23.4. But my own trip meter.. per full tank I get about 260 before I fill back up and that's when low fuel comes on. Ik I could go another 20-30 like that so let's say I'm getting 290 per tank. That's driving 75-80 for 216 miles.. just going to work and home on the highway

---------- Post added at 07:46 PM ---------- Previous post was at 07:45 PM ----------

Highway speed limit here is 75
 

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My 2005 4 Door Base Automatic gets only 26, but thats most likely due to the constant stop and go town i live in and the frequent hills i find myself climbing daily.

also i'm sure the hole in my bumper is causing some drag
 

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The extra gas you burn going uphill you save going downhill unless you use your brakes instead of down shifting.
 

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The extra gas you burn going uphill you save going downhill unless you use your brakes instead of down shifting.
Or even better, coasting and using the extra speed to help you up the next hill, if there is one - or even if it's flat, that's just a longer time before you need to touch the pedal to maintain speed.

That's assuming there aren't cops, that is.
 

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Kinda hard to downshift in an automatic with no manual mode lol. Do autos have DFCO too?
Yup. You can drop into I just fine and it'll engine brake.
 

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Nah, it's fine. It's no different than if it downshifted on its own. I do it all the time.
 

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The extra gas you burn going uphill you save going downhill unless you use your brakes instead of down shifting.
Interesting write-up, from the internet:

What's the most fuel-efficient way to go over hills?
Say I want to go over a series of hills in the most fuel efficient way. Should I accelerate downhills and use the momentum to go uphills (rpm variable)? Or should I just turn on the cruise control and not bother (rpm constant)?
Can somebody explain the physics involved here?

Eddie Xue, Honda Prelude driver
• Upvoted by Stephan Hoyer, Physics Ph.D, UC Berkeley

Most hypermilers have adopted a constant-throttle technique / driving with load (using a constant rate of fuel consumption) which gives a constant speed on flat ground, deceleration/using momentum on uphills, and acceleration on downhills back to your original speed. Basically you try to keep the engine and car as a system in its most efficient zone: avoid wasting energy on the downhill, avoid excessively high speeds that increase wind resistance, and avoid extracting maximum power from the engine (not the most efficient zone).

You need to optimize for the entire system, not taking the engine as a black box (which is especially untrue for gasoline drivetrains).

Essentially if you try to keep a cruise control, there will be a lot of wasted energy on the downhill: You will either let off the throttle all the way and use engine braking (possibly with downshifting) to slow down/maintain the speed, which throws energy away, or putting your foot on the brake pedal (frictional braking). If the hill is extremely slight, you may even need some gas to continue on the downhill with cruise control (you can avoid this by coasting downhill in neutral, since fuel consumption at idle is almost always less than the amount you have to give to continue accelerating).

Similarly, on uphills you will also be less efficient with cruise control by forcing the engine to operate in a usually less efficient range in order to produce more power (which will soon be wasted) e.g. downshifting a gear or two and seeing even higher RPMs in order to keep up the speed.

However in the name of safety and also to avoid reduced mileage from wind resistance, you may want to just let off the throttle on the downhill. If you do so, and you don't care about maximum speed, it will be more efficient to do so in neutral since in the vast majority of cases the engine braking effect will waste more energy than the reduce fuel consumption from deceleration fuel cutoff.

The reason why you don't want to slow excessively (to almost 0) near the tops of hills is because as your speed drops to 0, your fuel efficiency also drops. Most cars on flat ground peak from 35-55MPH * see graph at end.

Also on the uphills with constant load (deceleration), you will get lower speeds than the typical freeway 70MPH which will improve efficiency. Meanwhile, excessively speeding in valleys (accelerating too much on downhills) can hurt mileage by increasing your drag since air resistance is roughly proportional to the cube of speed, so 90MPH vs. 70MPH will have more than double the slowing force.

There is definitely an empirical observation and the exact characteristics will take into account individual cars' drivetrain, gear ratio, losses at each part of the vehicle transmission, drag coefficient, weight, the exact elevation profile of the hill, etc. it's very hard to say.

Example: On a short hill with a super torquey V8 motor (Camaro, Corvette) it may be beset to just accelerate up, since the efficiency range can handle that amount of torque. Meanwhile, with a weaker 4-cylinder Honda Civic you'd want to actively employ the "drive with load" method and lose speed on the uphill.
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For big trucks and RVs

The driving challenge: fuel-efficient hill climbs
When it comes to driving a truck up a hill technique is everything. How you drive can make a big difference to fuel consumption.
“Often drivers will attempt to increase speed while climbing the hill, and this is very inefficient,” says Andrew Low, Driver Development Manager, Volvo Trucks. “It requires a lot of more fuel, and in most cases it will only save you a second or two. Ideally you should hold a steady speed, in the highest gear possible, and then use the weight and momentum of the truck to push you over the top and down the other side.”
The key is to build up speed and momentum before you reach the hill, and then allow the weight of the truck to propel forwards on the downhill.
“The aim is to turn the hill into a flat line,” adds Low. “Of course we need to use more fuel driving uphill compared to keeping the truck moving on a flat road, but going down the other side we don’t need to burn fuel unnecessarily. We want to cover the same distance using the lowest amount of fuel possible, while also achieving an efficient speed.”
1. Anticipation
Climbing a hill obviously requires more speed and power. However the best time to pick up speed isn’t when you reach the hill – it’s on the flat as you approach the hill. When you see a hill approaching, begin to pick up speed so that you go into the hill with as much momentum as possible.
2. Avoid downshifts
Once you begin climbing the hill, you want to use the highest gear possible in order to use your engine to full efficiency. Try to carry a good speed but avoid accelerating. If your truck is equipped with I-Shift, then you can use it to lock the gears if you believe you can make it to the top without a downshift.
3. Roll over the top
As you reach the crest of the hill, release the throttle and allow the weight and momentum of the truck to push you over. The temptation will be to accelerate, but it’s far more efficient to allow the truck to roll over.
4. Coasting downhill
On the downhill, the momentum behind the truck should naturally propel you forwards. Use this to pick up speed, while consuming virtually no fuel. However, also read the road ahead and anticipate any obstacles. If you see a curve, it is better to reduce speed earlier, than wait and brake hard when you reach it.
5. Roll as far as possible
The heavier the truck, the more weight you have behind you and can use to push you forward. On the downhill, use this weight to roll as far as possible, and only accelerate when you begin to lose speed. Next time you’re driving downhill, try it. Once you’re up to speed, you’ll be surprised how far you can coast without even using the engine.
 
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