Per Pontiac Performance magazine (Fall 2007) p. 14


My Acura TL gets 32 hwy so I'm sure the numbers on the V6 are low. These are the TLs numbers: 17-mpg in the city and 26-mpg hwy.

You're not comparing apples to apples unfortunately.

First - your TL doesn't get 32 MPG hwy with the 08 EPA ratings. It gets 18/27 best, via the 2008 TL's.

Second - the TL weighs 3500-3600 lb. The G8 weighs near 4000 lb.

Third - Gear ratios. The G8 has a .75:1 5th gear with a 2.92:1 final drive, while the 08 TL 5spd auto has a .49:1 5th gear with a 4.31:1 final drive. Not sure what that equates to as to cruising speeds with an auto, but they are different.

I think the V6 numbers are right - it is a big ass car.

First - My point is that the EPA numbers are now more conservative than they use to be.
My TL does get better than stated EPA numbers. Additionally, I get better than stated numbers with my 2007 Solstice GXP.

Second - I did not compare the the TL vs. G8

Third - It is a big car, but I look forward to a test drive.

Well if you consider a G6 GT sedan weighs 3450 lb and with the 3.5L gets 30 mpg highway, real world. The GTP has the 3.6L and weighs a bit more, don't know the real world MPG on that.

Take the slightly more thirsty motor, add another gear and 500 lb....I dunno, I just don't see 30 mpg.

My GTO gets right on the money for 08 EPA ratings. Cruising at 80mph in 6th, I get 22-23 mpg - EPA is 23. City is 15 and while I can beat that shifting @ 2K & skipping gears, it is also pretty accurate.

Now I don't think 08 ratings are accurate for all cars. My wife's 06 Accord I-4 5spd gets 26-28 in the city, while it's rated for 23 now. But the Accord is a 3100 lb economy-based car with a gas-sipping motor.

Well if you consider a G6 GT sedan weighs 3450 lb and with the 3.5L gets 30 mpg highway, real world. The GTP has the 3.6L and weighs a bit more, don't know the real world MPG on that.

Take the slightly more thirsty motor, add another gear and 500 lb....I dunno, I just don't see 30 mpg.

My GTO gets right on the money for 08 EPA ratings. Cruising at 80mph in 6th, I get 22-23 mpg - EPA is 23. City is 15 and while I can beat that shifting @ 2K & skipping gears, it is also pretty accurate.

Now I don't think 08 ratings are accurate for all cars. My wife's 06 Accord I-4 5spd gets 26-28 in the city, while it's rated for 23 now. But the Accord is a 3100 lb economy-based car with a gas-sipping motor.

Interesting post, I have a couple of questions:

Wouldn't adding another gear ratio have a positive effect (or no effect) on mileage since it could allow lower RPMs cruising on the freeway without sacrificing acceleration?

Where did you get ’08 EPA figures for a ’06 GTO? Or are you just estimating what they would be if someone put an ’06 GTO through the ’08 test?

Yes, a 5spd auto vs 4spd auto could get better gas mileage - most greatly depending on the final cruising speed.

For instance, the 4spd auto in the G6 sedan w/3.5L V6 has a fourth gear ratio of 0.68 through a 3.05 or 3.29 final drive ratio.

The G8 V6 has a .75 fifth gear ratio through a 2.92 final drive ratio. I don't quite know how to calculate RPM @ speed on an auto, given torque converter slippage, but I'd say their cruising speeds will be similar.

In the end, more speeds in an automatic can provide a lower cruising speed but I think the biggest benefit is closer gears for better performance.

Seems to me that if someone is looking at buying the V6 over the GT for fuel efficiency, you may as well buy the G8 GT and enjoy the extra ponies. :D

^ True

or buy a Honda Accord

I have a 2008 Accord, with 4 cyl and an automatic. I get just shy of 30 mpg on the highway (NJ Turnpike, doing about 60 mph). Not quite as good as I would like, but where I come out ahead is in around town driving. Most of the around town driving is done by my wife and she gets about 22-23 mpg.

The Accord is a pretty big car and will fit full sized people in the back seat. More importantly, it easily fits 2 car seats, and 3 should squeeze in ok as well. (as you might guess, my family will be growing soon, so economy and space are my primary concerns right now!)

Hopefully in a couple of years, I will get an opportunity to consider something different. If I go G8, I will probably go with a used GT or GXP. Not really all that interested in the 6 cyl G8. Now, the new CTS with the direct injected 6 cyl... THAT is a car I would love.

I know that the post above talking about the Honda was a bit of a jab, but since thats where I am sitting, I thought I would throw in my 2 cents worth.

Greg

I made the same 200mi round trip to the Gulf coast as a month ago last week with the ODO @ 1850, now w\ODO @ 4200 I averaged 30mpg, or 1mpg more same load (3people w\overnight luggage) with speed at 65mpg...But a little less tire pressure than on previous trip.

It's all good!

Cheers!

Last time i checked, the G8 V6 averaged 25 MPG(Hwy) and the G8 GT averaged 24. True you might as well spend the extra dough for 2 more cylinders, but i seriously dont think its hard to squeeze out a little bit more than 25 MPG. It IS a V6 after all. Just drive like you have sense. Anyone buying a G8 V6 shouldnt be trying to drive harsh and rough anyhoo, in that case then the GT would have been a much better choice.

Last time i checked, the G8 V6 averaged 25 MPG(Hwy) and the G8 GT averaged 24. True you might as well spend the extra dough for 2 more cylinders, but i seriously dont think its hard to squeeze out a little bit more than 25 MPG. It IS a V6 after all.

And the G8 GT is a V4 sometimes ;)

With modern cars the size of the engine doesn't affect fuel economy as much as it used to. It's mostly physics: you have this much weight trying to punch this big of a hole through the atmosphere, and that takes x amount of power. As long as the engines are close in their thermodynamic efficiency, there's only things like gearing, friction, or pumping losses to make the difference.