Decent Highway Gas Mileage...
 

I think I got pretty good mileage on my 100+ mile trip from Colorado Springs back to Longmont.

http://i.imgur.com/B6UEG.jpg
45.9, got as high as 46.4 but the hills and stop lights kept running it down. Take off the 1-2 for the computer inaccuracies and its about 45 MPG.

This includes the several miles out to the high way with stop lights, climbing monument hill, a stop at Ikea, and several miles from the high way back home. Had the air conditioner on low for half the time and the head light on the other half.

This was to prove to a friend... "Its not what you drive, its how you drive it". Next trip will be back down at 30 mpg because its a hell of a lot more fun.

Whoa, going 45-55mph the whole time I assume? Takes some discipline to refuse to go faster than that in most cars haha.

Ha, that was 60-75, on roads with a speed limit varying from 55-75.

Its driving like my dad would, not fast not super slow...(in the slow lane with all the semis)

Damn you call that decent? Thats excellent mileage.

Wow that's actually really impressive. Maybe being in Colorado helps, theoretically holding 60mph at sea level will barely get you 45mpg or so. I think the air up there is like down 17% in density or something, that would be worth about 10% more fuel economy or so.

Could you see your reflection in the rear bumper of the 18 wheeler you were tailgating? ;)

(drafting can get you unreal mpg!)

Ive got a calculated 26+ mpg on my first few tanks in mixed driving. Then last tank I got 30! I haven't been afraid of revving it out either. Can't wait to see what it would do on the highway.

Dude you'd have to be drafting hardcore and going downhill the entire time to make this happen...

Sent from my Galaxy Nexus

You can't trust the mpg shown, since they tend to be off when calculating the average mpg (since they may not account for when the car idles, as it shows a blank "--.-" reading in those instances rather than 0 mpg, which is what is really what you get at that instant).

The best way to do it is to go by filling up the tank, driving, then calculating the mpg by taking the miles driven divided by the quantity of gas used to fill up the tank again. (It may not always be 100% accurate, but any variances will more or less get evened out.)

It's hard to tell, if the ECU could adjust perfectly it should be the same. Maybe the thinner air sits in a higher efficiency point of the FA20 for some reason. Would have to get a wide band o2 sensor to see if the ECU can get the AFR right.

The thinner air has less drag too, not that that is a big player on the twins cause of the .28 drag coefficient.

This is with a MT too, I wonder how well I could do with the AT gear ratio.

I would gladly trade whatever the high altitude affect is on MPG for the 34 HP it steals...:(

You're right, I had only used just over 2 gallons at this point and didn't want to refill up just to check MPG. The dash reading on mine has always been off +.5-2 MPG. (I still could tomorrow...)

Keep in mind the car may be more accurate than you think, gas stations are only legally required to be withing +/-10% on what they give you for gas. Since crooked corporations design the pump I would assume it always make it give you less gas than it says. There is no easy perfect way to measure MPG.

Toyota/Subaru have to be accounting for some of the idle time, because when you sit at a stop light, even though the dash says --.- MPG on the instantaneous screen, the average screen will decrease very slowly.

Sorry, but that's not true at all. That is a HUGE margin of error to begin with. And if that were really the case, people would notice with random tanks of gas being really terrible one week and really awesome another week but with the exact same driving patterns.

I actually have documented every tank of gas I've put into my car since I bought it, and I'd notice if there were something wrong.

The ECU does adjust. When the air is thinner, you lose power so you need a bigger throttle opening = less pumping loss. In a more abstract setting, having a lower starting pressure increases the maximum possible theoretical thermodynamic efficiency by increasing your "pressure ratio" although there's way too many things affected to say how this really affects the engine.

If the cruising power requirement were exactly the same you could expect maybe a couple percent efficiency increase. Since the air being thinner also reduces your aerodynamic drag (0.28 is pretty low for a production car but drag power is still pretty high at highway speeds) by 17%, your engine load just dropped like 9% (obviously depends on speed, which determines the ratio of aero drag to tire resistance). Since your thinner air is robbing more potential power from the engine than your cruising load has decreasing by, I think ~10% is probably a good estimate.

I remember some over sensationalist dateline stories about gas stations saying that it could be off by +/-10%, but after some random googling it looks like they are checked to ~0.5% every pump once a year. Looks like >90% of pumps are accurate when tested. So maybe .2 MPG variation...

1 internet point to you.

I have also wondered how accurate the pump auto click off point is, I have had random occasions where the pump would click off after 2 or 3 gallons even though I was on an empty tank.