cholmes1

I completely forgot about the weight difference With my IS350 I think it is 3527 which is still well under the IS-F. That would certainly have a sizable affect. I don't have an IS250 and really cannot see that being a fair comparison, but the fact that the IS-F is even close is crazy! With the IS350 being a significant step up from the IS250 I am even more impressed that the IS-F can have more than 100 bhp and still achieve these results on the highway with a controlled right foot.

For the poster who asked what the fun was with trying for 30mpg I would say that the money saved on highway driving can be used towards mods, fuel for racing, or anything else you can imagine. Since the IS-F requires the highest octane level, any money that I can be save is always nice.

Thanks for all of the posts...

ToothDoc

I thought the IS350 also needed premium fuel too. Also, the fuel economy is good for the environment, no gas guzzler tax, and really the fact you don't have to gas up as often. I hear M5s get 10-12 mpg and get something really poor like 150 miles per tank. Just going to the station that often would bother me. I do recall my ML500 being gassed up every three days!!! Weight doesn't have too much to do with MPG on the highway. More aerodynamics, and gearing. I bet if the IS-F had an even taller 8th gear, we could've gotten 30 mpg regularly. Honestly, I'd rather my IS-F's 6th gear be more like 7th gear and 7th gear more like 8th gear and have a super overdrive 8th gear like the Vettes. I notice that I can engage 8th gear at 45 mph but I wish it were closer to 55 mph. Then we can turn 1200-1300 rpm at 60 mph!

lobuxracer

iTrader: (2)

Low rpm != economy. Running in a very efficient part of the powerband to produce enough power to move the car does.

I've never seen north of 28 mpg in my F anywhere except downhill. Maybe there's too much alcohol in Georgia 93 octane.

mugenh22a4

iTrader: (9)

The best I got on any road trip was 28 mpg, cruising at 70. I don't know where these 30+ figures are coming from....maybe they were measured on a downhill?

melbitoast

iTrader: (1)

^^^
That's about the best I've seen as well. I'm going to Dallas for Christmas, so perhaps I'll try to control myself on that trip and get a better gauge on this.

cholmes1

Curious for to see how your trip to Dallas goes in terms of mileage Melbitoast. Keep us posted. Lobuxracer, not sure what the reason would be on why you could not duplicate the results of the other posters. In looking at the previous posts have you ever taken a pure highway trip and then calculated your mileage?

Understanding the efficiency as well as you seem to what do you believe to be the optimal RPM for the IS-F to run at 70mph? In my experience with my now gone 540i the lower the RPM the better...So I am curious why you believe that lowering the RPM during cruising is not the ultimate goal?

mugenh22a4

iTrader: (9)

+1 I definitely think the having the engine run at a lower rpm (as long as it's not luggin of course) has a greater effect on fuel consumption than does running at the engine's most efficient rpm.

Nevertheless, I'm still happy with the fact that my ISF can get to 60mph in under 5 seconds, and still return 26 - 28mpg on the highway.

Silver88

throttle smoothness has a lot to do with optimal MPG rather than specifically rpm. Use the current consumption gauge and smoothly use your throttle and you'll gain a few MPGs.

mugenh22a4

iTrader: (9)

Sure it does, but we're comparing 2 cars, assuming the same driving style in each.

ToothDoc

cruising at 60 mph on a calm day in 8th gear gives 30 mpg. On a cool day, not on a FREEZING day. I also like to have my tires inflated in the high 30s psi which I think gives me a touch less rolling resistance. Also, my car is usually very clean and waxed. Having said that, achieving 30 mpg is a lesson in driving like an old conservative grandma on the highway and something that is rarely achieved by me. I usually net 26-28 mpg because I can't help the occasional burst!

cholmes1

ToothDoc: Completely understandable given the cars power, however, the fact that it is possible is what I was most curious about. If you can do it in Northern IL on our crap roadways I think it can be done most anywhere (assuming the same fuel).

For those with coilovers or aftermarket springs, has anyone tried lowering the car and noticed a gain in MPG's. Obviously not the intention, but certainly would be a pleasant side effect if you knew you were going on a long trip.

Again, thanks to all of you who have posted. Really interesting to hear some of your results and strategies on how to be a fuel miser.

maj75

Unless someone posts a picture of the 30+ tank average display, I'm calling BS.

I know how to drive for mileage and averaged 23 mpg in my C6 w/ 6 speed doing mostly stop and go city driving. My highway mileage would give me 29mpg for a tank average driving 75-80mph with a couple of stops in between. I could get instant mileage of 33 (actual digital display) at 75-80 steady speed. I could go 450 miles on a tank of gas on the highway. The best I got on my GS460 was a tank average of 25mpg.

My 2011 only has 500 miles but I can't get over 23mpg for a tank average and that is mostly highway driving, 75-80mph. I am talking about the digital display of average mileage for current tank, not the BS sliding bar for instant fuel mileage. This is the first car I have owned in which I could not beat the advertised highway mileage by a substantial amount.

mugenh22a4

iTrader: (9)

^^ I wouldn't trust the accuracy of the OBC's mpg display. There's nothing more accurate than calculating the mileage yourself after a fill up.

cholmes1

Absolutely agree with mugen...The most accurate mileage gauge I have seen is in my Mom's prius, most other cars can be off from anywhere from 2-10mpg. For the real value you have to calculate it yourself after a fuel stop. Pretty easy and a guarantee of accuracy. Also a nice way to track your progress...

Joe Z

iTrader: (10)

Yeah especially when you fill up your tank and jump right on the FWY to a set cruising speed..

The MPG display can easily jump to the 30+mpg mark after crusing about 15 mins or more..

Joe Z