Real MPG

[Panzer Leader]

Ran a little test today. I had filled the tank to the brim, and ran it for 220 miles combined city/highway with mostly the AC on. I refilled the tank back to the brim. It took 10 gallons to fill. Using the age old method of simplemath, divided the Miles driven by number of gallons. Average turned out to be 22 MPG (all this without a calculator) I compared this number to the DIC which showed 19.3 average MPG. So do I assume that there is almost a 20% error rate? If there is, when I am on the road and the DIC is showing 27 MPG, do I assume I can add apprx 3 miles to that number? If so, then I am getting damn close to 30 MPG at 70 MPH with AC on AUTO at 75 degrees.:huh:

[WickedMom]

I did a similar test and got 25mpg with 430rwhp. So did I really get 28mpg? I will have to try this one and see. I used to keep up really well on my MPGTune.com mileage log, but gave up once I hit about 15k miles, my car seemed to be pretty close to the actual.
The gears in our cars like highway driving.

There are specifications/tolerances for gauge readings and I believe it is +/- 3 or 4 for the speedometer (thats why the digital and analog gauges are different). I guess the same would apply to other measuring devices.

['02 ws6]

On our trip to Colorado earlier this yr I did this same form of equating. On two it was in the 25.x range, and the last time was in 23.x (mountains a result).

Throughout I saw the DIC was about .5 - .8 mpgs off each time with the first two undervalued and the last stop it was overvalued. this could've been attributed to a number of things.

One being the fill level as I may have not filled it up to the neck like previous times or vise versa. I imagine they're pretty accurate basing it on real time fuel consumption l/hr (viewable in engineering mode) and distance traveled mph. Let us not discount human error and filled fuel level variables as there will undoubtedly be inconsistencies between each equation if not done the same way each time. Good that you maxed it out each time. I may have not done that.

At least it gives you a decent ballpark figure for those that are too lazy to do it the traditional way. : )

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[texn884]

The best I have got was 29 mpg running all highway miles from Ft. Stockton, TX to El Paso which includes mountains flat road and high altitude also. I was running 75 using cruise.
I am taking a trip from Oklahoma City to Fond du Lac, WI. and then back from Fond du Lac to Helotes, TX. I will report on each fill up. On average I get a good 25-26 and the car seems to get better mileage around 75-80 mph which I run 87 octane and it loves 93 octane so I switch off depending on cost.

[cwhite]

I always question the computer, since it's hard to say if it's a direct calculation, a weighted average, a moving buffer, etc...

I like this way of looking at it (too bad MPG is so trenched in our society, I don't ever think it'll go away). Pretty cool.

http://blogan.net/blog/2008/06/23/mpg-or-gpm/

[majesticix]

interesting article

[Panzer Leader]

Interesting video but no comment.

[caretaker]

Whenever I calculate actual miles per gallon used I usually get
about 1.5 to 2.5 MPG more than the DIC says,

[Panzer Leader]

Whenever I calculate actual miles per gallon used I usually get
about 1.5 to 2.5 MPG more than the DIC says,

That is what I thought, anywhere from a 10 to 20 % error rate. I wonder if the odometers have a similar error rate. Honda had a similar problem as well. Hate to think I will loose my outstanding GM warranty sooner than expected.

[Slyther83]

My guess is that the car's MPG calculator is about as on point as the tire pressure sensor... which isn't particularly on point at all, but gives you a close idea of what you're at.

[dblott]

Tire size and wear are a big part of speedometer/odometer calibration. I haven't done the math on ours yet, but if everybody is getting better than the DIC numbers, my 26.7-27.3 on our river road is really looking good. The one thing I did find out was at our first oil change the dealer looked at the info and said that we didn't require the expensive oil, (mobile 1), so we got the budget job. Our mileage for the same route dropped to 24.3 almost instantly. Thanks to you guys for the past discussion on oil, I decided at oil change #2, to go with M1. Instantly the mileage was back to 26.7 -27.3.

[johnh]

I've tested it a few times and found the DIC to be pretty accurate--within .5 mpg or so. I haven't tested in a while though.

[chuckie669]

my computer always seemed questionable. We took a road trip once and I filled it til the first click and then put another 30 cents to round the total. Showed I got 25.7-8 for the trip and was almost identical to the mpg calculation I did when refilling back to the first click.

[hflores3]

I did a similar test and got 25mpg with 430rwhp. So did I really get 28mpg? I will have to try this one and see. I used to keep up really well on my MPGTune.com mileage log, but gave up once I hit about 15k miles, my car seemed to be pretty close to the actual.
The gears in our cars like highway driving.

There are specifications/tolerances for gauge readings and I believe it is +/- 3 or 4 for the speedometer (thats why the digital and analog gauges are different). I guess the same would apply to other measuring devices.

I "really" need to set this thing on a dyno! I'm only averaging 18.9 mpg after the Maggie install. On the other hand (to be fair), Patrick G. simply loaded a tune (no dyno) to get me on the road! He should be able to find a "sweeter spot" once up on the dyno.

[WickedMom]

My average is about 18 with the LS9 injectors & moderate romping...


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[todds87ss]

I "really" need to set this thing on a dyno! I'm only averaging 18.9 mpg after the Maggie install. On the other hand (to be fair), Patrick G. simply loaded a tune (no dyno) to get me on the road! He should be able to find a "sweeter spot" once up on the dyno.

might also be the "testing" of the maggie...

[metoo]

I've only done this test once. My car is 100% stock. From full tank to fill-up, I went 247.74 miles. The computer said 16.1mpg, which means I spent 15.38 gallons. I filled up with 15.65 gallons for a calculation of 15.83mpg.

I've started a log to check the accuracy.

[SS DAVE]

have you guys checked your speedo accuracy against a gps?my car was out 4 klm per hour when new and stock ,so it mucks up the actual mpg ,since the mods ive done and had the speedo tuned to accurate [gps] the computer is also very accurate with mpg

[edmanet]

On the way to the track the dic said I was getting 23.8mpg. When I left the track [6 runs] the dic fell to 5.6mpg.......LOL

[WickedMom]

Lol. Limp DIC syndrome? Haha!

Yesterday I got 26mpg going to haddad Motorsports. After there I met up with some buddies for a canyon run and the mpg fell to like 14mpg... :(


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[BLKG8]

I use a andriod app called Mileage. It calculates mpg and cost of fuel..maint also. Oil change too. Avreges out fuel cost and mpg up to date of use....my low has been 8.2 ..high 28...car is stock..and wife drives it SLOW!..

Sent from my Galaxy S™...

[piecesparts]

I really must be doing it all wrong. I see a lot of 21 to 22 MPG and at times 23+ MPG. I drive on a lot of open highways with some city driving and I do run at speeds around 75 MPH as an average. I actually think that I get lower mileage at speeds less than 70 MPH.

09 GT Sport
Vararam air intake
MF axleback muffs
MF X-Pipe
computer tune for shift points and fuel map optimized

[Napalm]

Interesting. I just bought mine last night (yes used) so I am curious. Coming from a GTO I was wondering about this. The GTO was dead nuts accurate, especially after tunes. I never did any heavy engine mods. But I figured it would be close.

.

[texn884]

Not to brag but this was yesterday run of 440 miles running 73 MPH. I have the AFM in place and a great Patrick G Tune with the mods listed below. On average i get 24-26 on the highway depending where I am going but I love it when I can put these numbers down.

I get the same results sometimes at lower speeds like Piecessparts. 73 is a good speed for good MPG's but sometimes 75-80 I can knock down some good MPG's also. Nice warm weather helps a ton I feel.
http://i871.photobucket.com/albums/ab271/texn884/6199e4e4.jpg

[Napalm]

I can't even get mine above 21. I started a new thread here: link (http://forum.grrrr8.net/showthread.php?t=23974&goto=newpost#post353784)

But I think I put it in the wrong place.

[metoo]

I would love to know how the car calculated mileage. It's VERY FAR from the right way, whatever that may be.

Pre-modification (312whp), here are some examples of my stated mileage vs my actual mileage:
16.1/15.83
14.3/13.0
16.9/16.47 36.7mph
19.4/18.14 37.3mph
14.8/14.40 25mph
on a long trip to the tuner with modifcations in place but being very gentle since there was no tune = 26mpg stated

Post modification: Turbos (551whp) and 20" wheels (tires stock outer diameter, but wheels a bit heavier)
On the long trip back, tuned, being less gentle, but still not really getting on it = 29mpg stated.

Since then:
21.7/15.71 39.7mph
21.7/15.46 36.1mph
....and that trend continues. My actual is coming out around 25% less than the car states.

[todds87ss]

Don't know if it is a contributor, but I recently ran a test where I reset the DIC, ran 100 miles (work and back) with AC on. then did the same run after resetting the DIC again and ran windows down. Wind direction and speed was similiar to the first day. Windows down got 23.7mpg. AC on got 21.8 mpg. Almost 2 mpg by turning off AC. This might be effecting some of your tests.

[Chewy]

I drive 4 lane everyday with a bit of in town to get there and I average nearly 21 with an average speed around 45. My car reads high 19's, but my app reads high 20's.

[texn884]

I think a lot of that the dash reads verses when you fill up and caculate your fuel mileage will be different. I find that if I get a pump that can pump slow so I can get it all the way full to where I can see the gas in the filler hole. In this case my mileage will be less becasue I put in more gas becasue I wanted to becasue I have a long drive ahead of me and that extra gallon or two will get me farther down the road verses stopping someplace that has shit holes for gas stations.

I am easy on my car and yet it still puts out HP. It is no problem for me to get 25 mpg or better and now that it is summer I get to drive home in good head winds of 15-25 mph and I still can get 24-25 mpg. I am running 93 octane and Partick G. tuned my car for 87 but I find the Black Rat runs a lot better on it than 87 octane. I think the engine and transmission tune I got from Patrick G. has helped me save a lot of money on gas and makes putting expensive gas in the tank a bit easier on me since I put in a good $230+ per week in the tank and drive at least 1300-1500 miles a week. My week is 4 days and most of the time Friday is the cars day of wash and detail time since it gets the hell beat out of it from all the shit on the road and stones hitting my car.

My AC is on all the time and even in the winter sometimes becasue here in Texas it gets hot and I will not drive in 100 degree weather to think I am saving money, I want to stay cool and I hate driving with the windows down unless when I am on the last 2 miles before I get home and want to hear the pipes SING. lol

[Sephiroth]

I would love to know how the car calculated mileage. It's VERY FAR from the right way, whatever that may be.

Pre-modification (312whp), here are some examples of my stated mileage vs my actual mileage:
16.1/15.83
14.3/13.0
16.9/16.47 36.7mph
19.4/18.14 37.3mph
14.8/14.40 25mph
on a long trip to the tuner with modifcations in place but being very gentle since there was no tune = 26mpg stated

Post modification: Turbos (551whp) and 20" wheels (tires stock outer diameter, but wheels a bit heavier)
On the long trip back, tuned, being less gentle, but still not really getting on it = 29mpg stated.

Since then:
21.7/15.71 39.7mph
21.7/15.46 36.1mph
....and that trend continues. My actual is coming out around 25% less than the car states.

It's measured off injector pulse width, changing injectors will cause this to become un-reliable without a way to correct it cheaply. Certian gas stations contain more Ethanol than others (usually between 7-10%) which also accounts for a varriance. Considering the amount of difference you're experiencing, I would say it's normal.

the DIC in the A6 is measured off of 100% gas, which is why it's consistiantly off between 7-10% because of the ethanol for example..

that said, the caddy and G8 were always consistiant to within .1 mpg. I try to stick to exxon, as it's the only top tier in the area aside from shell (which is crap)

[Panzer Leader]

On the Tranny thread I posted some interesting data from the other day. Over 32.3 MPG@55MPH @1500RPM, Outside Temp about 92 AC set on AUTO Straight and level road. And the MPG was still climbing.

[texn884]

I use 95% Exxon/Mobil, good stuff.

[texn884]

Here is the fuel mileage I got this week. Drove 1,350 miles bought $197.00 in gas paid and average for 93 premium and got 26.4 MPG running 74 MPH unless I was in some towns in Oklahoma.

[Panzer Leader]

TEXN884, try using non-ethanol and see what the MPG will be. I am planning the route for the National Meet now. I am plotting in as many non-ethanol stations as I can. I only use alchol for drinking, wax removal on car paint and cuts. LOL

[texn884]

When I am in Oklahoma I get 100% gas and the mileage goes up a good 2 mpg.
Here in Texas there are not many places that dont have ethanol. I keep a spread sheet for each week and month and just added a MPG column and the car is just getting broken in at 83,000 miles. I will keep posting my mpg each week and conditions driving in. Seems now even in a good head wind the Black Rat can still get 25+ mpg. I Love it.

How do you find out what stations or cities have pure gas?

I feel my car is a test car for all my fellow forum members. It gets driven and and abused from road debris and keeps getting better and better.

[metoo]

It's measured off injector pulse width, changing injectors will cause this to become un-reliable without a way to correct it cheaply......

That was along the lines of what I was thinking. The computer sees a certain pulse width and assumes a given about of fuel passes. The same pulse for a "larger" injector will pass more fuel, significantly so the more your foots in it. The computer doesn't know that there is a higher flowing injector, so it bases the fuel use on the stock injector parameters. That's the way I believe it works.

[texn884]

Drove to El Paso today and first tank I got 24.5 mpg running 74 and fuled up in Ft. Stockton and got to El Paso and got 30.5 mpg running 74 mph.

http://i871.photobucket.com/albums/ab271/texn884/f8e4ed7c.jpg

[Panzer Leader]

Great numbers.

[texn884]

The Holden keeps impressing me. Screw the little compact coffins, I love my big horse power and comfort.

[Sephiroth]

I only ever got 23.5 in the G8, and that was babying it pretty good, oh how I miss even that number.

the V Managed a smige over 18 on the same trip recently.

[Slizzo]

I only ever got 23.5 in the G8, and that was babying it pretty good, oh how I miss even that number.

the V Managed a smige over 18 on the same trip recently.

Tune probably would have increased your mileage on the G8, maybe the same would improve your mileage on the V? Not sure how soft the car is from the factory.

[Seattle09GT]

If I baby the G8 and stay off the happy pedal, I can get 26-1/2 to 27 MPG highway.

In mixed city/highway I drop down to between 18-1/2 and 21-1/2.

In pure Hell stop and go, urban running, down to 15 MPG.

On track duty I average 5 to 7 MPG.

Overall happy. I'm running AFM disabled, Cortex tune, Volant, Solo, on 91 octane.

[Sephiroth]

Tune probably would have increased your mileage on the G8, maybe the same would improve your mileage on the V? Not sure how soft the car is from the factory.

I'm sure it would have for the G8, the V won't see a tune for a long time though, so I might as well get used to it.

[texn884]

I got 28.3 mpg from Albq. NM to Amarillo, TX with lots of mountain driving to get out of Albq.

[texn884]

I got home last night after a week of work on the road and put on 1,994 miles and got a overall average of 30.38 mpg. I spent $297.00 on gas.