i got about 450 to a tank with the cruize set to 80 from florida to illinois, and there are quite a few hills on that drive.

i think that is the biggest thing to get the most out of your gas is to use the cruize control.

 

Get to about 50 MPGs and then throw it into Neutral and just Cruise.

 

Thats not exactly accurate if you're car is running, lol. Thats the WORSE MPG

Seriously though, AT's can get around 30mpg if you put it on cruise control around 62 mph. Not sure about manuals but i would assume you could put her in 6th gear and cruise.

 

So driving from CO to AZ and finally here in CA.
Update.

Granny shifting at 2k rpm.
Both in 6th gear.
Driving around 80mph Avg. got about 25 MPG
Driving around 60-70mph Avg. got around 27 MPG

This is filling the car to a full tank then getting my miles and dividing and having a full car with luggage in it.

-Heading from CO to AZ almost hit an elk. Those guys are huge...
Was going about 80 and had to swerve to miss it.

-Going from AZ to CA Didn't know the highway got so close to the border.
Border police is funny. Its irony that border patrol were Mexican ^.^

Pics from my camera phone.
13337 miles at 69 mph fun with numbers..


Guess why I got pulled over!

He pulled me over for no front license plate >.<

Navi showing my "top speed"

 

This isn't a direct answer to your question, but it may help you pick a speed. I have a '03 6MT. I set my cruise control at 69 and I regularly get 30.3. I have gone well over 500 miles on a tank of gas with a few gallons to spare. I like to monitor my mileage so I usually fill up right at the entrance ramp to the freeway. I watch the average mileage on the Nav system. After a mile or two it shows about 28.5 mpg, then gradually creeps up after about 100 miles of driving, almost always maxing out at 29.9 to 30.3 at around 200 miles of driving. I'm guessing the slow increase in mileage is due to the car getting lighter as I burn off fuel and maybe the tire pressure increasing slightly as the tires warm up is a factor too. but I can't prove it. Just some seemingly obvious potential causes.

In really bad Philadelphia driving I can get between 19.5 and 21.5 mpg if I really baby the car, but not so much that I'm getting in the way of traffic. I only get 14-16 mpg from a tank full, if I drive the way we all like to drive our G's. By the way, my average speed in town is about 20-23 mph over a complete tank according to my Nav system.

I posted a tread about it a while back. It doesn't really answer your question, but you might find some useful information there. Here's the link.
https://g35driver.com/forums/g-spot/...ml#post3361670

 

I drive like I don't care about MPG and I can get ~400 on a tank...

Beyond that, I am not really concerned with squeezing the BEST I can out of it. It's a sports car, not a Prius.

 

50mph gives me best MPG... Downhill from there. Really downhill past 80.

 

I got 366.7 miles from fillup to low fuel light. I've been doing basically all highway driving, from home to work and back. The trip is 33 miles there and 33 miles back. Give and take a little bit of morning and afternoon traffic, I drove average 60-70 mph. I never floored it, and I did try to drive very passively. Don't reckon I revved it past 3.5k RPM's ever. And with all this pent up leadfoot envy, I raced a Ferrari 360 Modena on I-95 today after a fillup, little did I know he wasn't racing me.

 

Bump
Got 602 miles on one tank on my 2003 6MT sedan. All freeway. 30.7 mpg showing on the Navi. Average speed 64mph. Put 19.25 gallons in. WHEW! That last 50 miles was tense. Interestingly, my mileage started getting consistently better when the odometer hit about 50k miles. I guess it's broken in. I'm doing a little better in the city too. I used to get 12-14. Now I'm getting 14-16. Of course, I can do a little half-hearted hyper-milling and sometimes get around 18 mpg city, 22 if I drive like grandma. Living in Center City Philly is not good for my G. Burns up clutches, brakes, tires and costs a lot to operate. It's great on the road. Any hybrid would be really good for me since I do most of my driving in stop and go city traffic. There just aren't many hybrids that a self respecting G owner could even consider. New stuff is coming out all the time. I hope Infiniti has an offering akin to what Lexus has done. Put an electric motor on a big, honkin' V6 or V8 and call it a hybrid. If I could get 22-24 city I would be ok. I must confess, I'm getting more and more interested in the forthcoming Tesla Model S all electric sedan due in 2012. Costs pennies to operate, zero tailpipe emissions. Even counting the carbon generated at the power plant for the electricity you put in the car, it's about 1/10th. Tesla has a program where you can set up your own solar charging system and actually make a little money by selling your extra electricity back to your utility. the car looks good, can go up to 300 miles per charge (depending on battery option) and does 0-60 in 5.6 sec. There is no tranny, just a motor that turns 14k rpm coupled to a 10-1 reduction gear and 100% torque available at 0 RPM. It blasts off like a rocket. It costs 50K (after $4700 federal tax rebate). When you figure it is virtually maintenance free, it's equivalent to buying a $35k car, just about what I paid for my 2003 G35. I have loved my G but unless Infiniti gets in the hybrid/electric game I'm going to have to go elsewhere for my next car. I've never been a tree-hugger before and I'm still not one really, but the Tesla Model S looks tempting. By the way, the motor is between the rear wheels and the battery is the flat bottom of the car so you have storage in the back, and under the huge hood. You can carry almost as much stuff as an SUV! Their $100k Roadster sports car has been a hit. It's a sweet little ride that eats supercars that cost 2 to 10 times as much. But I digress. Sorry. A G with a 6MT can go far on 20 gallons without too much trouble.

 

52mph

 

6th gear cruising at 45-50 MPH on the long streets here in the San Fernando Valley (SoCal)

Unfortunately, SoCal freeways are either really fast (non rush-hour hours) or realllyyy slow (rush hour). My MPG takes a dump from there.

 

so OP you're the person who is driving in front of me in the fast lane going 60.. i see

 

Use your cruise control set at about 70-72 and you'll get over 25-30 mpg on flat ground all day in it. My best trip was a 5 hour trip to pa and I got 28mpg doing that.

 

It's not a "sports car". It's more of a "sporty luxury car".

"Sports cars" are much faster and handle much better.

I don't think it's unreasonable for someone to try and squeeze the most MPG out of it on a long higway trip.

 

On my way home from picking up my 06 last weekend I had the cruise set at 75-80 and got 29-30 MPG going north on I65 from Bowling Green KY to IN.

I don't look at gas mileage like I use to. I have had an 04 STi and an 08 STi and both of them were crap for mileage. I was excited to see those numbers. And I use gas mileage to tell me if the car is in good health too, you can get a good idea of how your car is doing just by checking your mileage at every fill up.