dmuellenberg

Agreed, but the only way to make sure all factors are consistent is to immediately turn around and make the same trip back. But I'm not going to do that just to back it up. Even then, since it is a 5 hour trip it still isn't going to be the same as it would be a different time of the day, winds can change during that time, etc. I'm not saying I get 33 mpg all the time, I'm just saying this particular trip I got that while I normally get 29-30.

On the return trip I got 29.8, but of course it was a different day and I had a 15-20 mph head wind versus no wind on the way out. Also, it is very flat going across central MN and eastern SD.

dmuellenberg

Actually the more I think about it, gasoline expansion doesn't make sense as far as the DIC calculation. It does make sense if you are manually calculating your mpg because when you refill the tank, it is going to indicate that you used less gas than actually used because it doesn't take the expansion into consideration.

But the computer calculates mpg based on the actual amount of gas consumed, not what is left in the tank. So while gas expansion would explain you being able to go farther on a tank of gas, it really shouldn't affect the mpg calculation (since if the gas expands then you have more gas in the tank).

For illustration purposes only, let's say you have a 20 gallon tank which you fill up. As you drive and use gas, the gas heats up and expands another gallon over the course of the trip. At the end of the trip you fill up and it takes 15 gallons, which really means that you used 16 gallons because of the extra gallon of expansion. If you manually calculate your mpg, your going to use 15 gallons so your mpg will be higher. But the computer calculates it based on the actual 16 gallons used so that calculation will be more accurate.

Does that make sense or am I off base here?

myvette_99

I agree 100% with you OP. Everyone else here is forgetting the biggest factor of the OP's awesome mpg....he was going 65 mph. Some of you are saying he could not have gotten that because you only get 28-29 or whatever, well you state that you are going 75 mph, that is the difference right there. Plus the OP said the winds were calm and the trip it pretty flat, again both of thoes factors play a huge role in the mpg of a trip!

JoesC5

The 18 city MPG and the 24 highway MPG(your numbers) are not absolutes as you seem to believe. If you were to take the time to read what GM printed on the windshield sticker(my Z06 has 15/24), you would see that it also says for my Z06 (under the city MPG 15).... Expected range for most drivers 12 to 18 MPG and (under the highway MPG 24).....Expected range for most drivers 19 to 29 MPG. Those are the numbers GM printed on the windshield sticker for my 09 Z06 in addition to the large 15/24.

So, the 28-29 MPG that get on the highway with my Z06 is within the spread that GM says is expected for most drivers.

Turbooo2u

I take issue with the OPs claim of 33.6 mpg on an extended trip. Just can't buy it, my friend's Aveo doesn't do that well...something doesn't add up. 28mpg in 6th gear under perfect conditions..I can buy that.

Chris Arnold

Some people just can't drive. I'm reading this because I'm considering a Z06 for my next car. I wouldn't expect a 427 to get the mileage that a C5 does, but with the cruise set at 65, the OP is pretty close. My C5 got a best of 38.8 (not a typo) real mpg (odometer/pump calculation) and 36 mpg (DIC) on a 12 hour drive from FL to OH, which is uphill, and the hills of KY and TN should have brought the mileage down. I believe it all comes down to cruising speed and technique.

Here's how to do it, in order of importance:
1. The single greatest factor for increasing mileage = speed. Stay below 55 mph and run in your highest gear. When hypermiling, I keep the vette at 50mph and give myself a + or - 5mph window to stay in. The ideal RPM would be as low as possible without lugging the car.
2. If you have a really sensitive foot, you can beat the cruise control, particularly in hilly areas. Plan ahead to coast down to speed for traffic, exits, turns, etc... Minimize brake usage. On the highway, you should avoid engine braking, and try to keep power to the wheels to maintain speed. If gravity is capable of maintaining or accelerating you, then pull the car out of gear or engage the clutch and coast. Use DFCO (deceleration fuel cut-off) only to regulate speed, because coasting and maintaining speed is more efficient.
3. Use the vents, not the A/C. Keep the windows up and let the air from the fans cool you, if the external temps are low enough to keep you comfortable. Use the a/c instead of the windows at highway speed, but only if you have to.
4. Tire pressure - hyper-milers say to run them at max recommended pressure. I don't trust that, and I think you'd end up wearing the centers out of the tires, plus the ride becomes more jarring. So I prefer to keep my pressure at around 32-35 psi warm. Tire pressure can make a huge difference if you are running low pressures. The difference between 35 and the 44 psi max, for example, is not as significant a difference as the difference between 21 and 30 psi.
5. Headlights off. Though this probably doesn't apply to C6s... The C5's pop-up lights are essentially air brakes and in my observations cost right around 2 mpg.

So before any of the douchebags chime in to say that 38mpg isn't possible in a C5, go out and do the things I just laid out and report back. Frankly, due to my lack of discipline and several extra stops along the way, I'm certain I could push the car over 40mpg in an all out effort to produce a high mileage number. So 33mpg out of a Z06? I say, sure. It's definitely plausible.

z51vett

On trip to Orlando Fla from Atlanta Ga pulled out on superslab set dic to zero and ran at 80 mile per hour and got 28 on the dic.
z51vett
Got 25 to gal in 96 impala ss using basic math method.

Turbooo2u

I thought the EPA used a very controlled enviroment for testing. I just can't see getting a 50% increase over the ratings. Even setting the cruise at 55mph in 6th on a flat surface with the a/c off. I've tried it and maybe saw a 2-3mph increase. The variations can't be that great between stock Vette engines.

JoesC5

He did say he normally gets around 29 MPG driving the same route. Under ideal conditions, I think he could get 33 MPG. But under normal conditions, the 29 MPG he claims is more realistic.

I've gotten my Z06 up to speed on the Interstate, then reset the DIC AVG and I can see 32-33 average MPG for 60 miles.

Winds are what will fool you. You can't feel it if you have a 5 MPH head wind vs a 5 MPH tail wind, but a 5 MPH wind will affect the MPG at 70 MPH on the Interstate by a couple of MPG.

In the early 90's I had a 1990 Sedan De Ville with the 4.5L V8. I could drive from Springfield, MO to Bartlesville, OK and get 28 MPG. On the return trip I would get 32 MPG. This was pretty consistent on every trip I made. But, there was always a wind blowing from west to east across Oklahoma and my gas mileage reflected it.

I was driving my Z06 west towards Oklahoma on I-44 and I could feel the head wind. Don't know what it measured but it was pretty strong. I was only getting around 24 MPG, where I normally get around 28-29 MPG.

Mr. Gizmo

I did a 200 mile round trip in my Z. The DIC said 27.3 When I did the math and re-topped off my car at the same filling station and at the same fuel pump, letting the pump click off by itself on each refuel and divided the gallons by 200 miles, It was 28.7 mpg.

During the trip, I had a couple of 2nd, 3rd gear bursts to safely get around some large trucks going up steep hills

My car is 100% stock.


I would tend to think the DIC was more accurate in my Z06 then the fuel pump or my solar powered calculator.

GMuffley

Whatever figure you have observed on a trip, we can all agree that the Z's fuel economy is astounding for a supercar.

CGZO6

My DIC MPG always goes way up after a couple of days at a road course track, then goes back to normal after a few days.

dmuellenberg

The highway rating on my 06 is 26 (not 24), so 33 mpg is only 30% above rating, not 50%. I've heard that EPA ratings are conservative, and the fact that I consistently get 29-30 mpg on the highway proves that. This is the first time I've ever seen it above 31.5 so it was probably a fluke due to ideal conditions. But I don't know why you find it so hard to believe that it could hit 33 mpg - it's not that outrageous.

JoesC5

The 2006 & 2007 Z06 26 MPG ratings were based on the old 55 MPH highway speed limit. In 2008, they changed the rating to reflect the current 70 MPH highway speed limits, thus the 24 MPG listing on the window sticker.

dmuellenberg

This is from my window sticker:

Actual mileage will vary with options, driving conditions, driving habits and vehicles condition. Results reported to EPA indicate that the majority of vehicles with these estimates will achieve between 13 and 19 mpg in the city and between 22 and 30 mpg on the highway.

Also from the Fuel Economy Guide:

EPA miles-per-gallon (MPG) estimates are based on lab testing
and are adjusted downward by about 15% to better reflect realworld
driving conditions for an average U.S. motorist.

ch47d1sg

recent trip in mine (1000 miles) average 28mpg at 80 MPH
Saw 30s when speeds were reduced to 65pmh

Despite the naysayers, it is poosible and plausible.

At the end of the day, congrats to the OP and everyone else believe what you read on the internet,,, ITS ALL TRUE

fly a Z06

Buying Chevron 91 at several stations and always using the gizmo for fasting filling I find that the pumps mostly click off when I need about 15 gallons. Sometimes they click off at 7 gallons and I turn the nozzle upside down and it will add the other 8 gallons.

For this thread is it possible that some station's pumps when clicking off are not actually filling the tank up completely which makes the math method inaccurate?

Trivia notation: After 5 1/2 years my 07Z just turned 59,000 trouble free miles and I've numbered every fill up receipt which is now at # 223. Lowest: $2.739 in Rolla. MO 8/07. Highest: $4.639 in Palmdale, CA 5/12.

Joel

Bill Dearborn

The problem with doing the math is you can't determine when the tank is full. Each time you fill the car you will get it full to a different level depending on the pump you are using, the temperature, the position of the car when the tank is being filled and how well you work to get the tank full. The tank has an expansion area above the spot where the filler pipe enters the tank. That area can handle quite a few gallons of gas. If the car is leaning toward the passenger side you can get more gas in the tank and if it is leaning toward the driver side you will get less gas in the tank. If the pump automatic shut off is too sensitive it will shut off too soon compared to other pumps that will let you run a few more gallons in. If the pump is running too fast due to having a clean filter it is hard to get more gas in because it burps back out at you. If the pump is slow due to a dirty filter you can ease more gas in by pumping it very slowly. Since we only have a 19 gallon tank the variance of one or two gallons on each fillup due to these issues can drastically affect the gas mileage numbers you calculate if you do it at every fill up. For the math to work out you need to take an average over 6 or 7 fillups to get close to the correct mpg number. Once you do that you see it approach the DIC avg reading.

Bill

Chris Arnold

In order to improve consistency and accuracy, I fill until there is standing fuel in the nozzle insert. I can actually see the fuel level at the top of the pipe.

why1504

IMO the DIC is as accurate as calculating the mileage using a calculator due to the above comments.

I have access to gas that has no ethanol in it. 91 octane. Car sounds better and "feels" like it runs better, pulls harder. It definitely gets better mileage. We find the best blended gas in our area to be Shell followed by BP and Chevron. If we are traveling we find the quality of the Shell to not be quite as good as our local Shell. This has been consistent with the Harley and the other vehicles we own.

On Sunday we drove 350 miles 85% was interstate. Average speed was 85MPH. I had multiple pulls above 100 an 2 runs over 100 for 5 minutes.

DIC reported 25MPG. Any way you cut it even at 20 MPG that is amazing. We have a 2007 Acura TL-S. It is quite comfortable above 100 mph. At these speeds it would not have gotten better fuel economy.