I am curious, has anyone used 87 or 90 octane gas?

And again 87 or 90 with the 10% ethanol gas?

 

is that Imperial?

 

I got 28.9 MPG (full tank, drove till fuel warning light and checked miles against fuel used) in my 2008 with manual 6-speed. The drive was from Ma to PA (Carlisle.) Can't wait to own a C7.

 

Nope, that's 37.0 miles per US gallon, as shown on the DIC. I've double checked my DIC to a hand calculation and it's right on the money for me.

 

I'm averaging 18 MPG but I'm also averaging 25 MPH. I'm in stop-n-go traffic at least 70% of the time.

 

I'm averaging about 19 with 2700 miles, same all around as my '08 Z06. At 70 mph my rpm and mileage figures are almost identical. Put me on the list for Eco delete with the associated weight savings.

 

 

Figuring mpg by gas station fillups is the only valid measure. The DIC is very optimistic based on my experience with my G8GT. I’ve seen 30mpg+ on the DIC, but that NEVER happens on a fillup where I’m usually averaging about 22mpg. Don

 

Hand-figuring accurate MPG is almost impossible from any practical standpoint. You may be able to get a pretty good "averaging in" over many fill-ups and lots of miles traveled, but you are unlikely to be able to report an accurate mpg rating for "highway economy" or any such limited-use reading.

Variables include gas tank expansion/contraction in different temperatures (surprisingly large and significant!), differing fuel densities and efficiencies between fill ups, inability to accurately fill to the same fill point each time, and differing vapor recovery losses in different temperatures and driving conditions.

That said, car computer MPG readings are also notoriously unpinned from any real world usage accuracy. They look at the amount of fuel sprayed through the injectors, which does not accurately line up with gross fuel levels in the tank. Amount of fuel going through the injectors doesn't account for any other losses in the process (evaporation, vapor purge, etc). So the cynical posters are correct that the computer numbers are typically higher than hand calculations.

It's a lose-lose situation. First order of business is to disregard all reported digits to the right of the decimal point! Second is to recognize that any reading (computer or manual) probably has a "truth" margin of error of anywhere up to 4 mpg.

In my earlier post, I just reported the DIC readings for convenience (including those silly decimal points). I'm comfortable that they are within a general order of magnitude corresponding to reality, but that's about it.

Whether you look at hand calculations or computer display, any given trip is likely to be swayed significantly by temperature, air density, direction and speed of wind, road surface, tire inflation, windows open/closed, and actual vehicle weight on the road while you're driving. Single-trip figures are for entertainment purposes only!

 

If everyone here compares their own DIC readings with other people's DIC readings it should still give an idea if you are getting better or worse than others. So even if the DIC is off by 5% (which I doubt it's that bad) it's still useful.

 

I hear ya, but as others stated the DIC maybe more on the C7 with DI.

Also I imagine a Z51 will have slightly lower mpg than a non Z51 that has lower numerical gearing either in the trans (M7) or diff (A6) on the highway.

 

hubby used to criticize me that I wasn't driving my 02Z "economically". Now that he has sold his C6 (auto)and waiting for C7, he is driving my car. Boy he sure doesn't drive economically!! Sticks are just too much fun. Your mileage will probably get better when the newness wears off. Besides Vettes are for driving like Vettes and not prius!!

 

One guy ask me about the mileage. My response. " I have no idea. I'm sure it's terrible because I just love to keep my foot on the floor going thru the gears in track mode."

 

 

Thank you! Finally some responses worthy of this delicious creation.

As great as it is that this car can get 25+ MPG... I am SO not even trying. That would suck the soul right out of this thing. Love to hear mine shrieking & spitting all day long.

 

I will go through the gears and drive it like I stole it.

But if I'm in crappy traffic where there's no option to drive it like I'd like, why would I not at least make the best of the situation and put on Eco mode?

 

I run a tank a weak through mine dic always reads couple mpg higher than hand figure. 380-420 miles and always takes @16 gallons to fill give or take .5 gallon. will turn 200k on Monday. best tank by hand figure was 31.7 Wallace ID- Portland OR

 

Just got back from a 2373 mile trip. Best MPG over 25 miles was about 31MPG (according to DIC). Average for the trip down was about 28MPG, in a Z51, A6 running in ECO mode for the majority of the trip, never used cruise control. Trip back was about the same, only the first half back was almost entirely in cruise control. Both trips were running ~80-85MPH, although DIC says average speed was ~60MPH not sure what is up with that. On the trip down, we stopped for the night in a hotel, and it did idle for ~10 minutes in the parking lot the next morning before we left, I suspect that played a factor in the MPH average. On the trip back, we didn't stop at all, and the MPG didn't change significantly.

I can only conclude that any reports of >31 MPG is done in a car significantly slower than 80 MPH, isn't a Z51, isn't an A6, is done while traveling entirely downhill, has a tornado pushing the car the entire way, or my car just burns more gas because it likes to. I'm happy with 28-30MPG in any case.

Onstar reports 24MPH for the entire trip, including a large number of short runs back and forth through town, through the dragon's tail, and the snake where I'm sure the MPG was very very bad.

 

80-85 MPH? 28 MPG sounds right.

I'm getting better than that, but I hardly cruise over 75 MPH. Most of the time, if I'm cruising, I'm averaging about 29-31 MPG.

If I can get the car on a long road trip, I'll know for sure.

BTW, my car is a Z51 7-speed.

 

I have only 500 miles and have averaged around 26 MPG, the mode have been 80% TR and 20% W, yet to use Eco.

BTW:I'm from East Taunton and car meetings scheduled in the spring?