This may or may not be a repost...

Per Pontiac Performance magazine (Fall 2007) p. 14

Start saving up for gas haha
just kidding

23mpg sounds a little low. Yeah, start saving for gas.

I get around 26-27mpg on the Interstate in my M6 GTO. I would think that the MPG would increase on a car with a better gearing, decent final drive ratios in the A6 and active Fuel Management.

23mpg sounds a little low. Yeah, start saving for gas.

I get around 26-27mpg on the Interstate in my M6 GTO. I would think that the MPG would increase on a car with a better gearing, decent final drive ratios in the A6 and active Fuel Management. Don't forget the numbers are the new EPA testing, so they may be a bit low. Our other car gets much higher than the rated 20mpg highway (we consistently get 25 to 26mpg highway at a good clip) and that is under the old system, but City was always under what the old system rated.

Well the Goat M6 gets 15/23 via the 08 EPA ratings. This sounds about right honestly, considering the GTO's M6 should cruise at a lower RPM (right?) with a lighter car, albeit with a more gas hungry motor.

Sounds right to me. And I get a max of 22-23mpg on the highway with Goat, cruising at ~80mph.

It's not low, as someone already pointed out this car and all 2008 vehicles are tested with the EPA's new method. It's also about the same as other V8 cars of it's size at different prices.

G8s are not a car you buy for fuel consumption.

I get this same thing with people who have BMW 5 series of Chevrolet Corvettes, people saying their V8 cars are getting mid 20s in highway mileage. I've driven many, many V8 cars before, and none of them achieve mid twenties unless you drive like a grandma (a grandma's grandma at that).

When lighter, V6 powered cars are getting low thirties, I dont think we need to be lying about this guys, ok? My parents, in their old age, are trying to be "hip" (their word, not mine) and search car forums for info on real gas mileage and what not, and my dad actually bought an Impala SS (the FWD version we have in the US) because people were saying that they got mid twenties highway mileage. It still beat his old truck, but he is getting 22 or so on the highway, and is pissed at me for ever introducing him to these internets. Lets stop the :gr_devil: speak, ok?

I get this same thing with people who have BMW 5 series of Chevrolet Corvettes, people saying their V8 cars are getting mid 20s in highway mileage. I've driven many, many V8 cars before, and none of them achieve mid twenties unless you drive like a grandma (a grandma's grandma at that).

When lighter, V6 powered cars are getting low thirties, I dont think we need to be lying about this guys, ok? My parents, in their old age, are trying to be "hip" (their word, not mine) and search car forums for info on real gas mileage and what not, and my dad actually bought an Impala SS (the FWD version we have in the US) because people were saying that they got mid twenties highway mileage. It still beat his old truck, but he is getting 22 or so on the highway, and is pissed at me for ever introducing him to these internets. Lets stop the :gr_devil: speak, ok?

I now have over 16,000 miles on my V8 – a 2007 Corvette w/A6 trans.
It is my only car & I use mine as a Daily Driver, commuter, etc.
Driven each work day ( perhaps 75% of my driving ) in & out of MidTown Atlanta, my driving typically includes some 70 to 80 mph cruising on the way in, at 6AM, and a 20+ minute ‘slog’ in very slow, bumper-to-bumper traffic moving at 0 to 15 MPH each afternoon.

My overall fuel mileage ( Excel = almost identical to DIC ) currently stands at 22.38 MPG.

I use the full 400 lb/ft of torque most every time I drive. Though typically not for more than short bursts – as I have no interest in annoying the LEOs.

In typical Interstate Highway style driving, I see 28 to 30 MPG in the ‘Vette, setting the cruise control at 75 to 80 MPH. I have recorded 3 full tanks ( primarily highway, with some light back road driving thrown in ) at over 28 MPG – one, with my Daughter & a long weekend worth of luggage calculated 29.04 MPG = 467 miles & 16.08 gallons.

Previous 8 cylinder Sport Sedans I have purchased were typically capable of 25+, when cruising at or below the posted speed limits.

I actually had a 2005 Grand Prix GXP ( Pontiac version of the Impala SS you mention ) and drove that car in essentially the same way I drive the Corvette. Even with DoD I would typically see 23 to 24 in the same highway mode where I see 28 to 30 in the Corvette. The Corvette is ( clearly ) lower & has less frontal area – and it is more aerodynamic - an issue at 75+ MPH. It also is geared to turn that 6.0L V8 slower \ at lower RPM than the 5.3L in the SS & GXP at the same speeds. As I posted elsewhere, my experience was that if you kept the 5.3L V8 cars running below about 65 MPH, they did return decent mileage = roughly the EPA Hwy rating of 27. At 75 to 80 MPH, where I find myself settling in on a long run outside urban areas ( speed limits 65 to 70 ), I’d see that 23 MPG to maybe 24 in the GXP.

And I have never posted anything but what I observe & calculate.

In fact, here is a very old GXP MPG Internet post of mine:

http://townhall-talk.edmunds.com/WebX?14@@.f0e0678/700!keywords=allin%3Amsgtext%20limit%3A.f0e0678%20 rayainsw

- Ray
Just one ‘data point’.. .. ..

I'm slightly surprised by these numbers. I mean, yes, it's a performance car. I just hoped the AFM and tuning it would balance out with the new EPA method and the resulting numbers would be like the GTO M6 numbers. So something like 17/25. I guess 15/23 is close. Just somehow the highway number going below 25 feels significant in my mind.

At this point I really want to know what the heck Pontiac plans to do with the manual. Is it coming? Ever? If so, when? And when it does, are the MPG numbers going to get better, worse, or stay the same. I will be driving this thing to work every day, and usually there's enough traffic that I can't drive like a bat out of hell. Work commute will be "grannie" driving. So I'm curious to know whether the A6 or M6 will result in better MPG in real life.

Amen Ray - fact of the matter is good gas mileage + big, powerful V8 is possible with the right gear ratios AND a light car. Vettes weigh 3100-3200 lb. The Goat is 3725 and the G8 is near 4000. That is a HUGE difference.

I'm thinking of trading to a used C6 down the road, this 17 MPG lifetime after is terrible!

uvaeeman - the GTO was rated 17/25 in the pre-08 ratings. The 08 EPA ratings put the GTO M6 at 13/22 or something like that, which frankly is pretty accurate.

Amen Ray - fact of the matter is good gas mileage + big, powerful V8 is possible with the right gear ratios AND a light car. Vettes weigh 3100-3200 lb. The Goat is 3725 and the G8 is near 4000. That is a HUGE difference.

I'm thinking of trading to a used C6 down the road, this 17 MPG lifetime after is terrible!

uvaeeman - the GTO was rated 17/25 in the pre-08 ratings. The 08 EPA ratings put the GTO M6 at 13/22 or something like that, which frankly is pretty accurate.


Damn, I didn't know it got spanked so bad with the new ratings. That makes the 15/23 seem better by comparison.

How could a car with better engine management, more MPG friendly rear gearing and a 6 speed auto get worse mileage? I'm talking about actual mileage. Not a number someone pulls out of their butt. Are they pulling a boat or going up a mountain? Those numbers sound so screwed. I averaged 27mpg highway with my V8 92 Camaro.

I have every receipt for fuel since the car was new. 16 mpg city and 26+ going 75MPH on the interstate is what my car gets. I bet I could pick up 1-2 mpg with a tune.

I get this same thing with people who have BMW 5 series of Chevrolet Corvettes, people saying their V8 cars are getting mid 20s in highway mileage. I've driven many, many V8 cars before, and none of them achieve mid twenties unless you drive like a grandma (a grandma's grandma at that).

89 Chevrolet Caprice Classic with a 305 TBI and an A4 would knock down 26mpg all day.

How could a car with better engine management, more MPG friendly rear gearing and a 6 speed auto get worse mileage? I'm talking about actual mileage. Not a number someone pulls out of their butt. Are they pulling a boat or going up a mountain? Those numbers sound so screwed. I averaged 27mpg highway with my V8 92 Camaro.

I have every receipt for fuel since the car was new. 16 mpg city and 26+ going 75MPH on the interstate is what my car gets. I bet I could pick up 1-2 mpg with a tune.
Automatic = more drivetrain loss - fact of the matter is, a 6-speed auto does more for closer gear ratios than it does cruising RPM.

Your 92 Camaro weighed ~3200 lb - I know, we have one. You simply can't fight weight - this thing is friggin' two tons!!

Automatic = more drivetrain loss - fact of the matter is, a 6-speed auto does more for closer gear ratios than it does cruising RPM.

Your 92 Camaro weighed ~3200 lb - I know, we have one. You simply can't fight weight - this thing is friggin' two tons!! We've got a 4860lb SUV that is a brick with a 311hp V8 with a 6spd auto, it is rated at 20mpg highway (old rating, new rating is 19mpg), but we constantly get 25 - 26mpg on the highway at 70 +, so, I'm thinking the G8 GT will do the same, and get better highway than published (other owners get similar higher milage on the highway). The SUV is an aerodynamic brick and a pig at 4860lbs, the VE has to do better.

This would be welcomed over my Trailblazer SS, rated 12city/16highway. Thanks in large part due to a 6sp vs. my 4sp trans, as well as a lower final drive ratio (why they put a 4.10 rear end in this truck is a bit beyond me), combined with the lower weight and Cd, as others have posted, seeing 25+ on a highway trip is likely very feasible

Some guys here in OZ have hit 8-9 Litres per 100km on the highway... (6.0L)

This is with the non DOD engines.

Say roughly 28mpg i think?

Some guys here in OZ have hit 8-9 Litres per 100km on the highway... (6.0L)

This is with the non DOD engines.

Say roughly 28mpg i think?

9 would be just over 26 MPG
8 would be 29.4 -
and I'd be impressed with THAT !!!

Here is the official numbers.

http://www.fueleconomy.gov/feg/compx2008f.jsp?year=2008&make=Pontiac&model=G8&hiddenField=Findacar

So 15 \ 24
Hmmm - not bad, actually ( IMHO )
Though I notice:
Premium Gasoline
Top center.....?????

Here is the context I see for these ( now ‘official’ ) EPA numbers:

G8 A6 = 15 \ 24 [ 2008 ]

Corvette A6 = 15 \ 25 [ 2008 ]
Corvette A6 [ 2007 ] WAS 17 \ 27
Would have been 15 \ 25 under the new \ 2008 EPA scheme

So.

I happened to fill my Corvette ( 2007 with essentially the same A6 trans. as the G8 GT \ V8 will have ) with gas on Wednesday morning & drove from where I live, northeast of Atlanta, to Macon & back. As I was approaching Atlanta on the return leg – after approx. 185 miles, the Driver Information Center AVG MPG read just over 31. This was driving ‘with traffic’ – mostly 65 to 75 MPH on the highway portions, with 10 or 15 miles of in-town traffic driving thrown in. Looking at the both the run down & back cancels out any effect of elevation change.

Thus, if the EPA highway rating for the G8 is accurate, I could expect roughly 30 MPG, in an identical run.

That’d be OK with me . . .

- Ray
We’ll see what owners report in the real world . . .

Plus these numbers are on 87 octane which saves you what $.25 to $.30 per gallon. That figures to about 25-26 mpg if you were paying for premium fuel.

That make any sense?

That may be a little high. running 87 in a premium recommended car will hit you for about 3% lower fuel economy. At least thats what it is in the LS2. so 1mpg roughly

Plus these numbers are on 87 octane which saves you what $.25 to $.30 per gallon. That figures to about 25-26 mpg if you were paying for premium fuel.

That make any sense?

It actually says 'Premium Gasoline" here:

http://www.fueleconomy.gov/feg/compx2008f.jsp?year=2008&make=Pontiac&model=G8&hiddenField=Findacar

Here is the context I see for these ( now ‘official’ ) EPA numbers:

Thus, if the EPA highway rating for the G8 is accurate, I could expect roughly 30 MPG, in an identical run.

That’d be OK with me . . .

- Ray
We’ll see what owners report in the real world . . .

It's getting deep in here. No way the G8 will ever get close to 30MPG. It weighs about 750 pounds more and is less aerodynamic than the beloved Corvette.

It actually says 'Premium Gasoline" here:

http://www.fueleconomy.gov/feg/compx2008f.jsp?year=2008&make=Pontiac&model=G8&hiddenField=Findacar

ah-ha. So by running 87, you'd lose ~1mpg off of that 24.

And Jerminator has a good point. An extra 750 pounds + a much higher Cd is gonna keep the G8 from anywhere near Corvette FE numbers

It's getting deep in here. No way the G8 will ever get close to 30MPG. It weighs about 750 pounds more and is less aerodynamic than the beloved Corvette.

I am well aware of the weight difference.
And I see that reflected largely in the ‘City’ number.
The frontal area is clearly larger than the Corvette – but I do not know what the Cd is . . .

And I could certainly be wrong.
As I wrote – we’ll see.

Yet, with the V8 tuned for a bit less peak HP ( compared to my Corvette ) and with DoD ( now called something else, strangely = AFM ) and with a target customer that likely has MPG as a higher priority than the typical Corvette buyer – I see the highway number as potentially achievable. It appears that ( for example ) the G8 V8 will turn 10% lower RPM at highway speeds than the Dodge Charger Hemi.

You don’t believe 30. That’s fine – just my “guesstimate”.

So ( as Maxwell Smart might say ) “Would you believe 29?”

I am just going by the only published ‘official’ numbers we have right now.

My point is that is there if a reasonably close correlation between my Corvette’s EPA highway MPG and real world highway MPG and the G8 GT’s EPA vs real world highway MPG, I’d expect to lose something, but not a lot . . . In that specific scenario I described.

- Ray
Happy to accept loan of a G8 V8 - to test my ‘hypothesis’ . . .

IMO - the EPA highway number wasn't broke, if anything it was on the low side, in our last 4 cars, they all consistently got better gas millage (3-5mpg more) than the EPA rating, all highway driving was in congested areas, and with lots of hills (when driving on LI with no traffic, as rare as that is, I would get even better due to the flat terrain).

I am no light foot, if anything, I like quick brisk acceleration and quick passes, I am definitely not the one to feather the gas.

I would think we could easily get over 27mpg on the G8 based on 24 EPA (especially now that it is lower).

But - only time will tell, and this is all conjecture now!

Don't forget the numbers are the new EPA testing, so they may be a bit low. Our other car gets much higher than the rated 20mpg highway (we consistently get 25 to 26mpg highway at a good clip) and that is under the old system, but City was always under what the old system rated.

need4spd: For comparison, what is your other car?

Even though its an aging thread....I still will comment..

Getting over the rated MPG means that you would have to drive exclusively on the highway. Mixed driving will never compute to 27MPG for the G8, just as it does not compute to 32 for my G6 thats rated at 29.

If you drive exclusively on the highway from fill up to fill up, meaning you fill up at a highway side station (on some highways at a rest-stop; on the I-81 through VA to NY for example) then you might see some impressive numbers. But don't count on it. I barely got to 32 in my G6, and I had to drive VERY conservatively. Limited my speed to 70MPH, didn't rush to pass, never put the pedal down hard.

And I calculated based on actual callons and distance travelled; the DIC figure said I was getting 40MPG when all was said and done. 8MPG off.... Imagine, that after 400 gallons of burning pleasure, at 40MPG my calculation would be WAY off. The odometer tells the truth. The DIC...in most circumstances...lies.

The DIC...in most circumstances...lies.
Hence it's name, DIC.

Even though its an aging thread....I still will comment..

Getting over the rated MPG means that you would have to drive exclusively on the highway. Mixed driving will never compute to 27MPG for the G8, just as it does not compute to 32 for my G6 thats rated at 29.

If you drive exclusively on the highway from fill up to fill up, meaning you fill up at a highway side station (on some highways at a rest-stop; on the I-81 through VA to NY for example) then you might see some impressive numbers. But don't count on it. I barely got to 32 in my G6, and I had to drive VERY conservatively. Limited my speed to 70MPH, didn't rush to pass, never put the pedal down hard.

And I calculated based on actual callons and distance travelled; the DIC figure said I was getting 40MPG when all was said and done. 8MPG off.... Imagine, that after 400 gallons of burning pleasure, at 40MPG my calculation would be WAY off. The odometer tells the truth. The DIC...in most circumstances...lies.

My DIC has proven ( through 20,000+ miles ) to be very accurate.
Always within 0.5 MPG, compared to odometer \ gallons & Excel.
And typically within 0.1 or 0.2 MPG.

As I stated previously, my basis for suggesting the MPG possible . .

ON AN EXTENDED & PRIMARILY HIGHWAY RUN [ Refer to my post #21 above. ]

. .could approach 30, is my current LS2 powered, 6L80 trans, Corvette EPA & actual MPG, the G8’s EPA MPG with L76 ( w/AFM ), & my expectation that a G8 GT’s “tuning” would likely lean somewhat more toward fuel efficiency that the Corvette.

I do not know what RPM your G6 turns at those highway speeds, but I’m guessing that at 70+ MPH you are turning somewhat higher RPM, compared to my calculations for the G8 GT. And beginning to ‘strain’ a 3.5L V6 - with 200 HP & 221 TQ ( 2006 numbers, I believe). The Corvette really seems to be ‘loafing’ at 70 – 75 MPH.

And the G6 rated at 29 Highway appears to have the ( relatively antique, now ) 4-speed automatic trans. Not exactly a paragon of efficiency, and ( in my driving ) subject to TCC unlock ( rev, gas guzzle ) at the slightest provocation. Not a criticism of your choice – just looking at the comparison.

“Mixed driving will never compute to 27MPG for the G8”

I do not understand where this comes from.

The ‘mixed’ EPA number for the G8 GT is: 18.

I agree that the G8 GT will not achieve 27 in mixed driving.
But I never said ( wrote ) anything like that – and I don’t recall anyone else posting an expectation remotely like that.

I typically refrain from discussing ‘city’ MPG, because there are way too many variables in the real world traffic situations and in what different drivers consider ‘normal’ in such driving. I typically confine my comments to reasonably well defined ex-urban \ freeway type cruising. Where the variables are fewer & I believe many drivers come closer to driving like the EPA tests.

If you can run at something like 70 to 75, preferably with the cruise control on (where safe - of course), and the highway is relatively level, with minimal traffic, I expect that one ought to be able to exceed the EPA highway number.

Looking at the trace ( MPH and acceleration ) for the newest version of the EPA’s test, I think steady highway runs of over 50 miles or so ought to allow one to approach 30 MPG.

Still, no member of the ( non-Press ) general public has even driven one around the block, let alone driven a well broken-in example for a trip of a few hundred miles.

So – I may be proven wrong. It has happened before.

But that is the logical basis for my ** GUESS**.

- Ray
Still in ‘wait & speculate’ mode . . .

You think your that important that I was commenting solely on your comment? ;)

All jokes aside, I was simply leveling my opinion that 27MPG wouldn't be so "easily" achieved as Mr. need4spd said. What I call mixed driving is not statistical 50/50. It can be 90/10, 80/20, 20/80, 10/100 (Hwy/city)... And besides, the G6 4 Speed is rated according to what the 4 Speed can accomplish. But strangely enough, its rated better than the 08 with a 6 Speed...

I drove a Grand Prix that was rated to 30, and never exceeded that 30MPG by more than 1-2MPG as hard as I tried. The DIC in that car happened to be a bit more accurate, though losing accuracy as MPG went up, but only slightly.

Add a V8 into the question and already MPG suffers. A good 6 speed helps, but when you've got over 700 pounds more "fat" than the Corvette, its going to show. This ain't a corvette. Sure, maybe some people will get close to 27MPG, but the word "easy" signifies that it would be capable of considerably more.

When I look at all the statistics, and how little pedal work it takes to subtract the MPGs at the top end of the scale, I believe that the 24MPG would be closer to the truth. I only achieved near 32 once. But in the same exact conditions, all it took was 10 miles to subtract 4.5MPG from that figure.

I am approaching it from a realistic driving standpoint; in which people are not going to be very often able to drive exclusively on the highways. However, in exclusive highway ideal conditions, 27MPG should be achievable or at least approachable. But I wouldn't bet my next paycheck on it.

And make no mistake, I would surely LOVE to be wrong.

"You think your that important that I was commenting solely on your comment? "

Hardly....
More later.
- Ray

Well I was just joking ;), but I thought I deleted that :p

That seems to be happening to me alot lately... :p

DIC for president!

need4spd: For comparison, what is your other car?Higgledy, it is a brick as stated in some posts before, a non-aerodynamic SUV Volvo XC90 V8, although it is a Yamaha engine, we have been impressed with the fuel economy (25-26mpg with a rating of 20mpg) with the 6spd auto on the highway (around town it is a pig, getting 13-14mpg though).

For the XC90, the V8 gets better highway fuel economy than the three variants of 6 cyl they put in it over the years (even the one with a 6spd auto also). Many other owners report the same thing on volvo forums.

Again, no one knows till we start driving the G8 to see what it will get. DOD could be a funny dog on this car.

I'm hoping the optimists are right. I'm no pessimist, I tend to hang around the center towards the "realist" sector.

But sometimes, I am surprised.... But I still don't think many people are gonna see a lot higher than 24. Lets face it, how much exclusive highway driving does anybody do?

Most of my driving is interstate. I work from home when I'm not on the road. My office is 150 miles one way.
I'd say I'm 85 percent hiway.
At home I can use the wifes Escape for around town.

Most of my driving is interstate. I work from home when I'm not on the road. My office is 150 miles one way.
I'd say I'm 85 percent hiway.
At home I can use the wifes Escape for around town.

That 15% will be enough to hurt your gas milage considerably. Just 10 miles city vs 250 hwy, and mine lost 4 MPG to 28, where it hit 32 in that same distance, where as with 249.8 Miles Hw2, .2 miles "on/off ramp" I scored near 32.

I stand behind my predictions. :)

I'm not going to argue your prediction. I'm not buying it for the fuel mileage. I just spend most of my time on the interstates.
At least thats the question I thought I was answering.

Well I don't want to argue... debating is more like it :p

Debates don't always have to be inflammatory pain hehehe...

Car and Driver averaged 16mpg overall in their G8 GT. This is not a car you buy if frugal fuel consumption is a high priority.

I expect people to get an average of 18-20MPG, since in reality they were pressing it. If you're gonna muscle it, 15MPG will be your likely figure.

If you take it easy in a mix I'd say 20.. If you take it to the highway mostly, I'd expect 21-22MPG... I don't expect many people to pass 24MPG.

Basically though, as stated above, I don't know who buys a car like this expecting fuel economy....

In retrospect, I don't even know why its being discussed with a V8 hehehe.....

...or debating it? :popcorn2:

Ave. mpg mixed should be 19 based on the stated numbers.

I believe the car will produce in excess of 19 mpg during most daily commutes with mixed driving.

However, if I do purchase one, I expect the first year to be below average. ;)

The first 500-1000 will be above average, then after that average, then after that 15... :p

One of the recent reviews i read.. stated that they used premium gas but that 87 was recommended.


Does anyone know why they would do that? If its recommended to run 87 why put in 93 etc?

Is'nt the HP rated at the 87 octane?

Would putting in 93 raise the HP number?

I was under the impression that Pontiac recommended 93 for better performance.

http://www.edmunds.com/insideline/do/Drives/FullTests/articleId=124876/pageId=136042#

"With that tank topped off with premium (GM recommends regular but says premium maximizes performance), our scales say 51.4 percent of the G8's weight is carried by its front tires. Pontiac says that evens out to a 50/50 split when there's a driver and a passenger aboard. We flogged it with an empty right seat and found the G8's balance to be ideal. There's good turn-in, slight understeer at the limit and power oversteer when you want it."


this is the exact statement. So how does it preform better? More HP when you add the premium stuff?

Was going to ask if Commodore owners reported a mystery power increase after so many miles like the GTO/Monaro. Since this car has a different OS, I guess the answer is wait and see. I assumed it was purposely programmed in on the GTO's.

Usually, it means more efficient combustion.

If the car is tuned for 87 octane, 91-93 isn't going to do anything for it.

Usually, a car like this has a computer with multiple tables.

Usually, a car like this has a computer with multiple tables.

Usually a car like this has two tables, a high-octane table and a low-octane table. The vehicle normally runs on the high-octane table unless bad gas (or low-octane fuel, in the case of vehicles requiring 91-93 octane) is put into the vehicle, at which time it drops to the low-octane table, preventing detonation.

I would be amazed if this vehicle had more than the normal two tables, including one that went unused unless the driver pumped in 91-93. Pleasantly surprised, but amazed nonetheless.

2 is more than one, so I called it multiple.

2 is more than one, so I called it multiple.

2 = 1 normal and 1 low, no allowance for higher than rated fuel.

Two tables means 2. Its a computer, it can be programmed for whatever the engineers see fit. If they wanted to put in a table for 96 octane fuel they could. Its not black and white.

Even though its an aging thread....I still will comment..

Getting over the rated MPG means that you would have to drive exclusively on the highway. Mixed driving will never compute to 27MPG for the G8, just as it does not compute to 32 for my G6 thats rated at 29.

If you drive exclusively on the highway from fill up to fill up, meaning you fill up at a highway side station (on some highways at a rest-stop; on the I-81 through VA to NY for example) then you might see some impressive numbers. But don't count on it. I barely got to 32 in my G6, and I had to drive VERY conservatively. Limited my speed to 70MPH, didn't rush to pass, never put the pedal down hard.

And I calculated based on actual callons and distance travelled; the DIC figure said I was getting 40MPG when all was said and done. 8MPG off.... Imagine, that after 400 gallons of burning pleasure, at 40MPG my calculation would be WAY off. The odometer tells the truth. The DIC...in most circumstances...lies.

The DIC is dead on in the C6 Corvettes. It was always optimistic by a mpg or 2 in the C5, but its dead on in the C6. I could not believe it, but was impressed with it.

Well, I would hope so in such an expensive car, wouldn't you? But most of us don't drive Corvettes, and most of these DICs don't seem to be that accurate.... regardless to who makes them. I don't know, I can't explain it. I just do the math :)

Well, I would hope so in such an expensive car, wouldn't you? But most of us don't drive Corvettes, and most of these DICs don't seem to be that accurate.... regardless to who makes them. I don't know, I can't explain it. I just do the math :)

How many GM cars have you had?:huh: Don't state most if you are judging from your car alone. I have had 3 GP's and my DIC was almost dead on, except for the oil life of course.

Usually, it means more efficient combustion.

Ok so what does this mean in real world driving?

Will HP increase? Will it get 2 mpg better driving?
Will it accelerate off the line faster?


For me i liked the fact that i could save some money at the pump by using 87 octane.

Two tables means 2. Its a computer, it can be programmed for whatever the engineers see fit. If they wanted to put in a table for 96 octane fuel they could. Its not black and white.

Actually, it is black and white.

Is there an ignore button on here?

What's your problem, I wasn't disagreeing with you. I was just saying, okay, I said multiple, I know that they use two. But they could put a third one on there if they really wanted to. Computers are not that limited. They can do alot with a chip these days.

Ok so what does this mean in real world driving?

Will HP increase? Will it get 2 mpg better driving?
Will it accelerate off the line faster?


For me i liked the fact that i could save some money at the pump by using 87 octane.

In real life, it doesn't mean a whole heck of alot. I've tried testing the difference in 87 and 93, and the results were too erratic to claim that 93 is going to get you noticable benefits.

The real benefit is that it burns hotter. Whether you're engine is tweaked for it or not, the hotter it burns, the less deposits left over. But not having inspected an engine after such a "test" I can't speak for that either.

So in reality, if its designed for 87, and gets 361 with 87; then there's no real reason to use 93.

How many GM cars have you had?:huh: Don't state most if you are judging from your car alone. I have had 3 GP's and my DIC was almost dead on, except for the oil life of course.

My family has been driving GM cars since long before the DIC was invented. The past 4 cars we've driven had a "DIC" of sorts, and none of them were ever "spot" on. The grand prix was the closest. And at only .5MPG off, I don't consider that bad at all.

But the G6, and the LeSabre both tend to exaggerate the figures. You can doubt me all you want, but from my observations, they aren't all that accurate. Its not difficult to calculate.

When my G6s DIC says 27MPG, I know I'm getting around 24-25MPG... usually somewhere in between. To me that's significant. Because every time I do the math, it ends up being at least 2MPG off, and the higher it reads, the more its off by.

Now its not gonna make me not buy a car... its hardly even worth worrying about. I was just saying, in my experience, they typically lie. *shrug*

I have to agree with you on that one, 2-3mpg is excessive. Since the DIC in the G8 is HUGE, maybe it will be more accurate:p

I hope so :) I personally like it when I can count on the digital display being correct, or at least within an acceptable margin.

on a flat wide cali road....on easter to my brothers..about 100 miles total..i set the cruise control at 65 mph - got passed by everyone...but it said i got 25 mpg the whole trip
thats fair enough for me...im tired of people complaining or arugeing about the gas mileage though..driving around town at lunch i get 14 mpg, so what...its a performance sedan..i didnt buy it for the mileage.......my old bb elcamino got 10mpg and i loved it.sorry im on vicodine..and ranting.going strir crazy at home.. i had eye surgery and cant even drive my new g8 today :(

on a flat wide cali road....on easter to my brothers..about 100 miles total..i set the cruise control at 65 mph - got passed by everyone...but it said i got 25 mpg the whole trip
thats fair enough for me...
i had eye surgery and cant even drive my new g8 today :(

Thanks for posting this.
What you describe ( everyone passing you ) is ** EXACTLY ** why I am curious about steady cruise MPG at a more common highway speed.
Meaning:
75 +\-.
Really am curious if AFM \ DoD will still function ( well \ at all ) at 70+ MPH…
Hope your eye(s?) heal quickly…
- Ray
Just curious – not obsessed . . . ????

thanks JAW!

I do all highway driving, 70 total miles a day, 5 days a week. So if I could go 350-375 miles on a single tank, that would be outstanding, getting 24/25 miles a gallon. Right now I am driving a neon as my daily driver which is getting 29/30 lol. But I can only go about 290 miles on a tank before filling up, which is like $30. The G8 is what, like $50 to fill up? Gas in NJ is $3.00/gallon

I'm averaging 19mpg in a mix of highway and fairly congested city driving. That's with a fairly heavy foot as I learn the new car and enjoy the new power.:driving:

thanks JAW!

I do all highway driving, 70 total miles a day, 5 days a week. So if I could go 350-375 miles on a single tank, that would be outstanding, getting 24/25 miles a gallon. Right now I am driving a neon as my daily driver which is getting 29/30 lol. But I can only go about 290 miles on a tank before filling up, which is like $30. The G8 is what, like $50 to fill up? Gas in NJ is $3.00/gallon

NJ (as an average) has the cheapest gas in the United States as of right now. Lucky you!

I am sorry to report that some of the pessimists/realists are more accurate based on my experience. On a 1000 mile trip with cruise set at 80, the V8 was only good for 21 mpg. Not sure if the AFM was still working at that speed, it didn't seem like it, but sometimes I don't notice.

I think anything over 70mph it will decrease quite a bit. I actually don't think 21mpg at 80mph is bad at all...

As far as the DIC goes, my TBSS and the G8 are both off (under) by .5mpg.

I am sorry to report that some of the pessimists/realists are more accurate based on my experience. On a 1000 mile trip with cruise set at 80, the V8 was only good for 21 mpg. Not sure if the AFM was still working at that speed, it didn't seem like it, but sometimes I don't notice.

I am sorry to report that some of the pessimists/realists are more accurate based on my experience. On a 1000 mile trip with cruise set at 80, the V8 was only good for 21 mpg. Not sure if the AFM was still working at that speed, it didn't seem like it, but sometimes I don't notice.

That seems about right considering my experience with the GP GXP AFM. What type of terrain? (flat, mountains, etc.)

Chip

It was flat (Illinois, Wisconsin). And not that I am totally upset with 21, its just not the 25+ that was tossed around.

I have NOT connected my laptop to this new car, but all GM vehicles I have seen had mild fuel maps form 650-2000 rpm, and switch to aggressive mapping for 2000-4000 rpm then another for beyond 4000 rpm.

Eitherway, keep revs below 2000 rpm and the computer will continue using the mild maps and push timing advance to 33-35 degrees. I will have to hook up the laptop when I get the car back to see if it still works this way for 2008 GM vehicles.

I have connected my laptop to this new car, but all GM vehicles I have seen had mild fuel maps form 650-2000 rpm, and switch to aggressive mapping for 2000-4000 rpm then another for beyond 4000 rpm.

Eitherway, keep revs below 2000 rpm and the computer will continue using the mild maps and push timing advance to 33-35 degrees. I will have to hook up the laptop when I get the car back to see if it still works this way for 2008 GM vehicles.

Fascinating.
Because the best information I’ve seen says that 80MPH = JUST over 2,000 RPM.
2020 RPM, in fact – based on the C+D data panel.

Please do post what you see?
It would be interesting if the change \ ‘cutoff’ for the fuel map means that at 75 MPH and approx. 1900 means you’d see 26 MPG,
And at 78 and 1970 RPM you’d see 25 MPG,
but at 80 and 2020 RPM you’d see a drop – to only 21.

And:
It looks to me ( see link below ) that the “new & improved” ( ? ) EPA tests, the “high speed” portion includes only one very brief ‘spike’ to 80. The rest of the test, while at higher speeds than in the past ( was max. 60 MPH ) would allow the G8 GT to remain below 2,000 RPM.
For the cruise portions, at least – not the acceleration portions . . .

Thanks,
- Ray

http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

Also:

Is there an 'Instant MPG' display available in the DIC?
If so -
Has anyone watched this during flat highway cruise
at various speeds?

Thanks,
- Ray
Would conduct the expirament, myself - if only I had a G8 GT available ....

We took a road trip this weekend and got in between 22-23 mpg on the hwy. We didn't maintain a constant speed (still breaking the engine in, kept it below 68 mph as per the manual) and had a pretty stiff headwind. The LS series engines have a history of not being fully broken in until after about 2,000 miles, so I will view the mileage as set in stone until after that point.

I have to upgrade my AutoTAP for the new CAN protocol access and HPTuners since it is in a new car added to my cable. I am splitting the costs with a friend I just have to get him on board since we co-own the existing products.

I forgot to type "NOT" in my post as I haven't connected to it, but I have tuned 1996 trucks, 1999 trucks, 2002 and 2004 V8 Cars and trucks as well as 2005-2006 trucks.

A feature the exists in our ECM's but disabled is "Lean Cruise". The Australians get to u se since they don't follow the US's stricter EPA guidelines. What it does is at a set speed (65mph for example)..in 6th gear..the ECM will lean out the fuel mixture in an attempt to increase mileage. It causes the CATS to heat up beyond recommended ranges as a result, but increased Fuel Economy.

No mileage figure is going to be accurate until there is several thousand miles on the car. My CTS, which has the same v6 that's in the G8, didn't fully loosen up until about 12K miles. With the cruise control set at 70, I got 28 mpg. Mixed driving is 19-20. this car was rated 18/27 by the EPA under the old system. I think the new CTS is rated 17/25.

I think the GT could do nearly as well with cruise, as it is effectively a 4 cylinder at steady speed. And the new EPA rating are a lot lower.

Just finished the first tank with 15.1 MPG but that was with several, ok numerous displays of power and speed.


Did I mention this car is amazing!!!


I picked her up on Tuesday evening for MSRP...

I have to upgrade my AutoTAP for the new CAN protocol access and HPTuners since it is in a new car added to my cable. I am splitting the costs with a friend I just have to get him on board since we co-own the existing products.

I forgot to type "NOT" in my post as I haven't connected to it, but I have tuned 1996 trucks, 1999 trucks, 2002 and 2004 V8 Cars and trucks as well as 2005-2006 trucks.

A feature the exists in our ECM's but disabled is "Lean Cruise". The Australians get to u se since they don't follow the US's stricter EPA guidelines. What it does is at a set speed (65mph for example)..in 6th gear..the ECM will lean out the fuel mixture in an attempt to increase mileage. It causes the CATS to heat up beyond recommended ranges as a result, but increased Fuel Economy.


Thanks for droppin' this knowledge. This would be cool if this were enabled on the U.S. spec ECUs......

Very insightful.

IMO - the EPA highway number wasn't broke, if anything it was on the low side, in our last 4 cars, they all consistently got better gas millage (3-5mpg more) than the EPA rating, all highway driving was in congested areas, and with lots of hills (when driving on LI with no traffic, as rare as that is, I would get even better due to the flat terrain).

I am no light foot, if anything, I like quick brisk acceleration and quick passes, I am definitely not the one to feather the gas.

I would think we could easily get over 27mpg on the G8 based on 24 EPA (especially now that it is lower).

But - only time will tell, and this is all conjecture now! This has been my experience also.