The answer is both. It takes more gas to make more power. At higher RPM, the engine has much more internal friction to overcome, which takes more gas, but you can also lose efficiency running the engine too slow, since it's most efficient in the mid-range. There's no simple answer.

9.3 MPG is ridiculous. If you're sure that you're correct in your measurements, I'd start looking for technical issues, maybe starting with that lead foot

 

I really can't get my head around you guys attitudes to driving at 30 and 40MPH with the RPM at 1200-2000 in high gears, on a dead flat road you may just get away with it being relatively economical, but under most circumstances its going to cost you MPG and wear on the engine.
Any engine has a best working RPM for a given gear ratio, different types will be slightly different, IE a high reving Honda V-tech will need to be reved to achieve good power delivery and economy as it peak torque will be a lot higher up the RPM range, whereas a big V8 will make a lot of torque at a much lower RPM, but even that big torquey V8 will have an ideal RMP to get ratio.

The VQ35DE engine has similar characteristics to a V8, in that it makes good torque at relatively low RPM, BUT the 6MT and the autobox are still designed to be on the sporty side, in that they should be revved to get the best from the engine in both power delivery and economy.

I just don't know why you buy a sport GT coupe and then drive it like miss Daisy.

 

Just cause it's a 6MT doesn't make daily drives into a race. It's just a different way to drive, but hey, that's just my opinion

 

I would cry if I got 8mpg in the city. I get better mileage in the city than I do going 75 down the freeway. It's all about how you drive your car

 

Same here. I like to drive economically when I'm just using the car like an appliance to get from point A to point B, but when I want to have fun, I go all out (and get significantly less than OP's 9.3 MPG). I recently averaged ~28mpg over a 6800 mile drive, which was mostly highway and maybe 200 city miles, but I've also gotten 7mpg putting down faster lap times than poorly driven Ferrari 430's at the track with my G sedan

 

No-one said anything about racing... Coasting up to lights uses more fuel than using your gears and doing 40 in 6th

 

NEVER ride the clutch this will just wear it out quicker and cost you $000 in the long run.

You should take each gear 1,2,3 up to about 2000rpm until you get to the speed you want. Why shift into neutral at all?? All this does is you loose engine braking and the engine has to put fuel in to keep it ticking over. If it was in gear no fuel is injected to keep it turning over- this is costing you mileage with your petrol!!

YES you should stay in 4th alot more at 40-50mph, maybe even 5th going down hill. This way the engine is hardly straining to maintain a constant speed. You can easily get 25mpg out of these cars!!!!! If you were in 6th gear at this speed the car would be "bogged down" trying to turn to higher gear at such a low speed. It's unneccessary strain on the engine.

Try and see it as this for day to day driving:
1st gear= 10mph
2nd= 20mph
3rd= 30mph
4th= 40mph
5th= 50mph +
6th to maintain 130+mph , or just cruise at 60mph all day long.

Try and leave dipping the clutch until the last minute when approaching a junction. The car will not stall unless your in a stupidly high gear. You can then select 2nd gear with a little rolling momentum and pull away fine.

If you need to overtake something this is where you would drop it down a cog say form 4th to 3rd. Get all the poke out in 3rd it'll easily do over 60mph in 3rd gear..

Have you actually learnt to drive in a manual car? As all the above should be covered in lessons etc

These car don't need an overdrive function (unless maybe auto) but then these have sport mode surley? No one should ever be in 6th gear at 30-40mph. It'll break your engine and coke it up in the longrun.

The only faulty bit here is the driver using the wrong gear. Don't bother trying the 6th gear wonder mpg idea. It isn't. It will only make you look a dick when the car breaks I would love to come over there and show you guys how to get the most out of your cars. You would be shocked....

For the record i've driven a manual for 10yrs (UK and all my driving life) the past few have been in a 420bhp skyline which i can get to return 26mpg on a long trip. Round town this drops to 15-20mpg and at the Nurburgring it went down to 7mpg, yeh thats right 7 Our gallon of fuel now costs us £6+ which is like nearly $8 so were looking at $75-$80 to fill our cars up. When driving them properly i can get about 180-230 miles out of a full tank (traffic depending). So every bit counts!!

 

Unless you put the pedal to the floor every time the light turns green, it seems like something might be wrong with your car...

 

Which car? It's all got confusing lol......

There's nothing wrong with the Infinity G35. It's just the very poor driving style and understanding of using the correct gear for speed thats killing the mpg.

There basically a 350Z (what we get over here in uk) with a different badge and 2 more seats. If they did 8 or 9 miles to gallon i don't think many would sell over here due to the cost of fuel

 

I meant OP's car, not the G35 in general. My bad lol.

 

Also the quality of fuel will impact on mpg. The lower MON rating you guys use, is it 93, 95, 98 over there?? The better the fuel like super unleaded plus the smoother and more economical your car should be... You don't see Athletes eating a McDonalds when there training do you?lol. What you put in affects what you get out.

I use shell V-Power only as it's the best we can get over here (98-99RON) and it's what the car was set upon. It will run on other super unleaded fuels but i don't reckon there as good...

Whats OP's user name can't seem to find it-unless it's in the signiture bit haha....

 

thats like v10 numbers....

 

^^^Whats like V10 numbers??

 

You'll have to excuse us americans, apparently we don't know how to properly address a post we wish to reply to lmao.

I think theo was referring to the OP, as 8mpg could be considered mileage for a larger displacement v10.

Towards the OP, you should be shifting at about 2.5. If really trying to conserve gas, its possible to wind up to like 2.1. The main thing is the keep these cars over 1k. Obviously you would still bog if you mashed the gas, but even at 1.2k you dont have to feather the throttle. I live in a relatively small town with like 11k people, with a mostly highway commute @ 45mph. I get into 6th as fast as possible and just cruise the the CC. The traffic lights on my commute are fairly spread out, and by knowing the length of them I can just downshift to the correct gear I know will engine brake me down with out having to use any brakes. Of course if you cannot drive correctly, don't bother because by missing a downshift by even a couple hundred RPM is far worse $$$ wise than using the brakes.

 

Still sounds to me like you guys are driving the wrong cars, you need Toyota Prius
Driving like that is just a waste of a capable car,I still drive my 350GT/G35 without regard for fuel prices (about double yours)
i would rather leave it parked than drive it like that.