My car is ignorant of aerodynamics.
 

I have been driving in the fast lane at 70-75 MPH significantly more because I have college in the morning the day after I have night classes and I like to get more than 4 hours of sleep. I expected to take my lumps and get 33 MPG, but noooo, at 38.7 MPG, my car insists on getting the best fuel economy I have seen without any mods or P&G.
I find this odd since my fuel economy doesn't seem to increase much when I drive 50 or 55. I guess I should check my tire pressure to see if it has anything to do with it.
Ooops. I forgot a word from the poll. I must be more tired than I thought.

I'd be curious to know what your engine's BSFC chart looks like compared to a HP/speed load chart for your car. If I had to guess, I'd say you're managing to land on or close to that "island of efficiency" that occurs with a thus-and-such torque load at so-and-so speed, and that just happens to be at 75mph.

Grab it and growl, man. Laugh all the way to the bank at high speed.

There are rare cases of BSFC being low enough to overcome the additional power required to go faster. I've really only seen one on paper and that was a ~1997 Celica and it got like 1-2 mpg more at 60 vs 55.

well thats easy
 

my whole project was built around this concept.
It is called re-engineering, if your car was designed for initially another market or target buyer it has been purposly drawn away from its true capabillity. The engine creates best power and economy at a point determined by cam, timing, exhaust flow, injector flow and patterns, load etc. etc.
Long and short is gearing or final drive ratio possibly from tire dimension etc. etc. Is in a certin rpm. your car doesnt defy physics it simply is purpose built to that speed. If you know its sweet spot then you could drop tire diameter slightly and get it into perhaps 67 zone where laws of physics are not punishing the economy. Ill bet you get +8 mpg with that if you really are looking to save fuel. Or do you enjoy watching for the cops so much at current speeds of your life.
I hope you understood all this muck well enough.
My project by the way was reversed Im trying to lower RPM into 67 - 69 zone and stay in peak powerband of engine...
Thanks for posting this alot of people never see this side of eco modding they just do this or that and get lucky of not.
This part takes real finess unless you are rockett scientist type.
Or worked on race cars etc.

i've seen a few instances of this happening before. when it comes to recent vehicles, i seem to remember at least one chysler product that peaked around 80MPH.

This is an interesting one from the aspect that you haven't done anything to the car...it just seems to be that way from the factory. My only question would be: are you now driving with traffic? In that maybe its the fact that you are driving in the wakes of other cars who would normally pass you. Driving slower seems to keep me in "fresh" air a lot more than I ever was when I drove 65-75mph.

If you did mods, this next story might mean more but it has the same lesson to be learned - lower RPM doesn't always burn less gas. So my Monte Carlo SS came from the factory with a 305 engine and 3.73:1 rear gears. When it was my only car I wanted to get better mileage than the 15 I was getting because I had a summer job coming up that was going to require a lot of highway driving. I found a rear out of a Malibu with 2.29:1 gears in it (probably didn't have an OD trans) and swapped in the whole rear. Did some math and found that something crazy like 1600RPM was 65MPH. I drove the first 2 tanks at theoretical 65mph and get like 10mpg. Did some reading and found the Monte engine is more efficient in the neighborhood of 2 - 2500 rpm. Started driving faster to get into the "ecoband" of the engine and my economy shot up 25mpg. After doing the some more fuzzy math I figure that I was doing a little north of 75mph but that the car "felt best" a little north of 80mph...either way, I was passing everyone and getting 25mpg with an engine that never got better than 15 for me. I think they were rated at 21 from the factory... Sometimes it doesn't make sense but I wasn't about to complain about getting places faster and burning less gas doing it :)

has the length of your commute changed / getting fewer cold starts per tank now?

the only way i've ever found to get better mileage by going faster is by pacing other vehicles after they pass you, but its only worth a few mph, varying by the vehicle youre following

I'm running a .815 fith gear, a 3.73 final drive if the order code on the trunk is to be believed, and tires that run my car 10% faster than stock. My timing might be a degree past stock. I do accelerate at 80% throttle using the 3000-4000 rpm range and glide with the engine on in 0 net power requirement situations (downhill, rolling up to a light,) but that is normal for me. I'm surprised because I normally see my fuel economy drop like a rock at high speed. I need to get around to installing my MPGuino to figure out what is going on.
Working off this chart (the previous engine is the 7a-fe or 4a-fe) my lowest BSFC is still quite high.
http://ecomodder.com/wiki/images/6/6...1zzfe_bsfc.JPG
My commute hasn't changed, I actually have to deal with more traffic now vs the spring.

what spif said.

i do better at 60ish, in line with a semi or other traffic than i do on my own at 55.

I think Toyota 4 cylinders like to rev higher. I noticed it in my '02 Corolla (1zz-fe engine, the same as the earlier BSFC chart), shifting at higher RPM gave me better fuel economy, and faster acceleration to boot. Didn't have Torque yet, so couldn't monitor engine parameters. With my Yaris, I've noticed the same thing. I've been shifting at low RPM because the Yaris seems to have a better low end torque vs vehicle weight ratio, thinking it would give me better MPG, but need to break the habit because shifting at higher RPM gives me the same or better momentary fuel economy, as measured by Torque, but gets me up to speed and into high efficiency cruising faster, so I use less fuel to get to speed and increase my average FE. I've found Torque to be accurate but a little low when it comes to MPG measurements; my long term average on Torque is 36.8, while my calculated is 36.9. I also see little change in momentary FE going 60 mph vs 70 mph, hell, I even still get about 40 mpg going 80 mph.