# M6 vs A4 highway mileage



## widetrak (Sep 27, 2004)

I am considering getting a '05 GTO with the automatic (or maybe a '04 if I decide I shouldn't wait on a LS2). I've noticed with the LS1 '04s the M6 mileage rating is 17/29 while the A4 is 16/21. I imagine the LS2 will be comparable. 

Does anyone know why the automatic's highway mileage is so low? The LS1 in the Vette and F-bodies did not have such a drop in highway mileage when going from M6 to A4. The T/A's with M6s are 19/28 and the A4s are 18/26. 

I've got a '88 GTA with the 5.7/A4 and a '01 T/A with the M6. Comparing the two, I know my next car will be an auto, but the GTOs low hwy #s are alarming considering what that engine does in the F-body. 

Thanks,
Brent


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## rock421 (Aug 7, 2004)

Not sure yet why the mileage is so different, but don't forget about the $1000 gas guzzler tax on the auto. It's like rubbing salt into the wound.


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## George8211 (Sep 21, 2004)

I tried to find out why that was... Both the A4 and the 6 speed have the same final drive gear ratio. And the A4 has a 'lock up' torque converter once in 3rd.

:confused


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## rock421 (Aug 7, 2004)

George, the 4L60E trans has an overdrive ratio of around .75:1. The six speed trans actually has two OD gears. Fourth gear is 1:1, fifth is around .75:1, and sixth gear is .5:1. 
The final drive ratio for the auto trans car would be approx 2.60:1 and the manual would be 1.73:1. The F-bodys had the same setup, so I still don't know why the auto trans GTO suffers so much. Maybee someone will come up with an answer.

Brian


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## George8211 (Sep 21, 2004)

Hey Brain... Your right... opps, heres the ratios, is this amount enough to make that much differance in MPG?

Even though is article is for the 2005 the ratios are the same as the 2004

http://www.newagegto.com/05GTO.html


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## muohio (Sep 22, 2004)

George8211 said:


> Hey Brain... Your right... opps, heres the ratios, is this amount enough to make that much differance in MPG?
> 
> Even though is article is for the 2005 the ratios are the same as the 2004
> 
> http://www.newagegto.com/05GTO.html



That's a 30% difference in gears which is enough to give that difference. Something else to look at is the range for highway driving of both cars. The number on the sticker is an average, but sometimes that range is more telling.


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## rickglow (Sep 28, 2004)

what kind of mpg is everyone getting? i have 600+ miles and havent averaged over 15 mpg with half of my driving on the highway. i havent driven it hard and still no increase.


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## Luth (Sep 28, 2004)

rickglow said:


> what kind of mpg is everyone getting? i have 600+ miles and havent averaged over 15 mpg with half of my driving on the highway. i havent driven it hard and still no increase.



16-18 mpg by the tell tale little gage. I drive through the city on 'backroads' 25-45 speed limit (I'm usually 5-10 over the limit). I haven't had a chance to go on a long distance trip with it to see what it will get on the Interstate yet though...


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## kevracer (Sep 27, 2004)

*Mileage*

I have taken two extended highway trips with my GTO so far, with approximately 800 highway miles. Average MPG on those trips is 20, according to the digital gauge. I have yet to compare to amke sure that readout is accurate.


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## lisatw151 (Sep 8, 2004)

I've also taken a couple of trips in my M6. Went to S Georgia last month... approx 450 miles one way and averaged 25mpg according to the digital thingy. That was doing 65-85mph pretty much the whole way. I think my average speed for the trip was 76. In town, I'm averaging 17mpg.


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## capra2d (Aug 3, 2004)

rickglow said:


> what kind of mpg is everyone getting? i have 600+ miles and havent averaged over 15 mpg with half of my driving on the highway. i havent driven it hard and still no increase.


I just completed an 1,100 mile round-trip between Phoenix and El Paso, including a 170 mile mixture of freeway and city street driving. My M6 had 2,700 miles on it at the outset. Since we were in no rush to get there or back, I wanted to see what fuel mileage I could squeeze out of it. Driving very conservatively and with the cruise set at 65, it got 25.5 mpg overall. The highway-only mileage was 26-27; the city-only was, and has been, 17-18. The stop-and-start is a really thirsty process. These are manual calculations. Try as I may, I'm not always able to fill the tank completely, thus the ranges.

It's not terribly exciting driving at 65. Then again, it's pretty sedate at any legal speed--a testament to the seating comfort, etc.


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## NEW2GTO (Nov 3, 2004)

An acurate figure for fuel mileage on a new car is kinda tricky. Most new cars, GM ones especially, are set to run very rich to clean out the cylinders of any burrs and such from maunfacturing. I think somewhere around 11-14k they are supposed to automatically lean out. I may be off on the mileage. That is what a dealer told my dad when he bought a 2002 GMC a few years back.


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## Afterglow (Nov 1, 2004)

*Good gas mileage*

I've almost got 2K miles on my car (M6) and so far the MPG has varied quite a bit depending on my driving habits. I drove to Detroit and back to Lansing which is about 160 miles. I was averaging about 90-100mph and still got 22mpg. I normally drive pretty aggressive even in the city and average about 15mpg. Last week I decided to try to conserve gas, so I've been shifting earlier and keeping the rpm's around 2k or less and my mileage is 19mpg currently. At 45mph you can cruise along in 6th @ 1000-1250 rpm's
City driving in Lansing isn't anything like Chicago or NY or LA so use this info however you like.....its just my 2 cents.


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## GTO TOO (Sep 10, 2004)

NewtoGTO,
The dealer is full of well ground cow droppings. They run stoich out of the box or they won't pass emissions. The open loop fueling does not change with mileage either. Man some dealers will say anything just to get a customer to forget their issue.What the dealer was counting on was, all vehicles break-in and improve MPG over time. He just fed your dad a song and dance and hoped the mileage improved before he returned. The other large issue with fuel economy is weather. If your dad bought the vehicle in a cold weather area, the warm-up on all engines is richer longer based on start-up temerature. As the weather warms less time is spent at a richer A/F during warm-up. Here's another hint most folks stop measuring fuel economy after the "new car" wears off. So the dealer may have counted on that as well. Running rich to "wear off burrs" is BS. Running too rich and the fuel washes the cylinder walls and would significantly SHORTEN an engines life. I must say I've never heard that tale before so it ranks right up there with chrome exhaust bearing !!!!!!


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## GT MECH ENG (Jun 3, 2005)

muohio said:


> That's a 30% difference in gears which is enough to give that difference..


So I guess the million dollar question would be; why in the world would pontiac make a 4-speed auto with such a high a final drive gear ratio?


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## JTYLER1604 (Jun 3, 2005)

My thoughts are that if the final gear was made to support better gas mileage, that the 0 to 160 mph times would decrease, which would be unaccceptable by any standard. LOL


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## JMVorbeck (Jun 1, 2005)

Curious that GM put a 4 speed auto in there, arnt most modern autos 5 speeds now? I read in C&D that one of those new Kraut cars (BMW or Merced's) stuck a new 7 speed auto and with only 300 some HP that car (heavy as it was) has some sick acceleration that was almost seamless.


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## diverdan (Apr 27, 2005)

There is some parasitic loss from the auto tranny, but I think that extra gear primarily makes the difference. I bet the 07 (if there is one) will have a A5.

If I turn on the instant gas mileage I can putter around and get 23 mpg or so in town and 26 mpg at 65 mph. Thats a far cry from the 31 mpg at 65 mph I can get in my Z06 (as if I could drive that speed for any length of time).
Normally I turn off the instant gas mileage, because I don't like looking at it, so I imagine my mileage is usually worse than that in both cars.


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## GT MECH ENG (Jun 3, 2005)

diverdan said:


> There is some parasitic loss from the auto tranny, but I think that extra gear primarily makes the difference. I bet the 07 (if there is one) will have a A5.
> 
> If I turn on the instant gas mileage I can putter around and get 23 mpg or so in town and 26 mpg at 65 mph. Thats a far cry from the 31 mpg at 65 mph I can get in my Z06 (as if I could drive that speed for any length of time).
> Normally I turn off the instant gas mileage, because I don't like looking at it, so I imagine my mileage is usually worse than that in both cars.


Pardon my dumb question, but what is "instant gas mileage"?


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## GT MECH ENG (Jun 3, 2005)

JTYLER1604 said:


> My thoughts are that if the final gear was made to support better gas mileage, that the 0 to 160 mph times would decrease, which would be unaccceptable by any standard. LOL


True, but throwing a 5th gear in the A4 would not hurt performance in any way and would help fuel economy. It seems logical that there should be a 5th gear in the A4, but of course as we know is the case with any business, sometimes money comes before reason.


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## JTYLER1604 (Jun 3, 2005)

I agree 100% that there only 4 gears in this gas guzzler is a poor choice. And if a 5 speed could improve mileage enough to eliminate that gas guzzler tax, it would be worth it to the consumer, even if it jacked up the price of the car. They could just have a $0 option, auto or manual, and raise the price of the car.


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## JTYLER1604 (Jun 3, 2005)

GT MECH ENG said:


> Pardon my dumb question, but what is "instant gas mileage"?


On one of the modes on the DIC, what I've learned is the Digital Information Console or something, basically the digital display located above the steering wheel, it will display the instantaneous gas mileage. So when you're your hard on the gas at high rpm's it will read lower than when you are idling down the road. I think.


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## diverdan (Apr 27, 2005)

JTYLER1604 said:


> On one of the modes on the DIC, what I've learned is the Digital Information Console or something, basically the digital display located above the steering wheel, it will display the instantaneous gas mileage. So when you're your hard on the gas at high rpm's it will read lower than when you are idling down the road. I think.


What he said.


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## toolman (Jan 10, 2005)

I have the auto and I average 19 mpg on mostly mixed travel, I took I drive a week or so ago that was highway roughly 150 miles round trip and got right at 24 mpg. I conducted my own test and filled the car up about a month ago and drove it like a Grandma for a whole tank, got 20mpg, then the next tank I drove it like I stole it an got 16.5mpg.


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## Big Red (May 20, 2005)

Got my 05 m6 2 weeks ago and the gas mileage stinks. Granted I live in Los Angeles, I do not have commute on the very congested freeways, surface streets only. I guess the stop start of stop lit streets does'nt help. I'm getting only 10.5 a gallon. I've got only 850 miles on her so I'm hoping for little better mileage in the next couple of months. By the way I have'nt been really romping on the throttle yet, I get to depressed watching the gas gauge move. :willy:


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## JTYLER1604 (Jun 3, 2005)

Big Red said:


> Got my 05 m6 2 weeks ago and the gas mileage stinks. I'm getting only 10.5 a gallon. QUOTE]
> 
> Dude - you need to recalculate your calculations or take that thing back to the dealer because something is wrong.
> 
> Generally speaking it sounds like whether you drive it like you stole it or take 'er easy, the mileage is not much different - it sucks. May as well not worry about it and drive as one pleases, in my opinion.


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## b_a_betterperson (Feb 16, 2005)

Big Red said:


> I'm getting only 10.5 a gallon.


My car got fairly poor mileage out of the box -- but I'm up around 19/20 combination driving now. Relax and give it time.


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## JMVorbeck (Jun 1, 2005)

Absolutely right. I got about 10mpg for the first 2 weeks and went through 6 tanks of gas. I thought I made a serious mistake for a daily driver. Now I average 18.5 during my daily work commute and 25 on the highway trips I have taken. I am much happier now.


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## JTYLER1604 (Jun 3, 2005)

I have 350 miles on mine and am getting about 16 last I checked and have been driving it fast at times so I was surprised someone else was only getting 10.5 driving conservativly.


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## JMVorbeck (Jun 1, 2005)

JTYLER1604 said:


> I have 350 miles on mine and am getting about 16 last I checked and have been driving it fast at times so I was surprised someone else was only getting 10.5 driving conservativly.


I never said anything about conservativly.........


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## JTYLER1604 (Jun 3, 2005)

Big Red said:


> I'm getting only 10.5 a gallon. I've got only 850 miles on her so I'm hoping for little better mileage in the next couple of months. By the way I have'nt been really romping on the throttle yet, I get to depressed watching the gas gauge move. :willy:


This was the post I was referring to regarding driving "conservatively." Sorry for any confusion.


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## toolman (Jan 10, 2005)

JMVorbeck said:


> Absolutely right. I got about 10mpg for the first 2 weeks and went through 6 tanks of gas. I thought I made a serious mistake for a daily driver. Now I average 18.5 during my daily work commute and 25 on the highway trips I have taken. I am much happier now.


 :agree Same here!


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## ronaldvetteron (Nov 9, 2004)

6500 miles on an 04 M6 running CORSA Sport and Lingenfelter CAI. I consistently average 20.5-21 mpg in my daily commute of 40 miles round trip. This as 2 stop lights and several stop signs each way. I average about 50-55 mph and shift at 2500+/- on average with a couple runs up to 3,000-3,500 each tankful. On the highway, no run longer than 100 miles and I have seen 24+.


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## Braman'sGTO (Mar 14, 2005)

What you guy's are getting is not that unusual, I only have about a 2 mile run between my house, daughters daycare and my shop and it is all stop and go. About the time im up to speed its already time to get on the brake and im not even running in any traffic. Tippicaly I get anywhere from 10.5 to 14.5 MPG, if im running the highway it is a completly different story were talking 26-27 MPG by the time im down to half a tank. The only time I get on the highway im going a few hunderd miles so its not a fluke, I can say that I do about 1 mpg better if im not using cruse control. Some thing that you guys may want to check is to see what kind of gas milage you get at higher speeds, I have noticed that I get better gas milage on the highway doing 85 versus 65, these cars like high speeds.


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## JTYLER1604 (Jun 3, 2005)

Braman'sGTO said:


> Some thing that you guys may want to check is to see what kind of gas milage you get at higher speeds, I have noticed that I get better gas milage on the highway doing 85 versus 65, these cars like high speeds.



AWESOME


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## fergyflyer (Apr 18, 2005)

One of the questions was why did the F-body with an automatic do better than the GTO with an auto. The answer is the F- body had 2.73 or 3.08 standard rear axle ratio and a 3.23 as the performance gears with the auto, and 3.42 with the 6spd. Our GTO has 3.46 for auto or stick. 

I've been getting better mileage as the car ages, I'm guessing that the engine is breaking in and I'm stepping down less to make it go. It started out at 15-16 mpg and is now up to 17-17.5. On the highway I'm getting 21.5, but haven't checked it for a while so it may step up. 

By the way the computer has set-up mode that is richer. It would run in that till it has enough data to set-up the fuel trims. This would happen over the first 50 or less miles. It might make a difference on the first tank, but that would be it.

I'm hoping to get the mpg up to 25 highway and 18 for my normal driving as I learn the car. It's so much fun to hit the loud pedal though. How many of us bought this thing looking for great gas mileage also?


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## gclcpa (Jan 9, 2005)

*2004 A4 gas mileage*

My GTO had 15 miles on it when I bought it on 1/22/05. It now has almost 9,000 miles on it. My commute is 37 miles one way, mixed driving. Our office moved over the weekend, and I sit in more traffic now, and it is over 40 miles one way. This tank, if it holds out as it currently stands, will be the worst ever. It is averaging about 19.1 mpg on the avg mpg readout. 

I have checked my mileage versus the computer readout, and have discovered that generally it requires around .3 of a gallon less fuel to fill it up than the display indicates. Therefore, my actual mileage is slightly higher than the computer display.

On the whole, I averaged between 20 and 21 mpg. My worst prior to the current tank was 19.7 and my best was around 22. I have not had a chance to take it on a road trip yet, so I don't know how it would do at higher average speed, but I suspect it would be around 24 mpg.

I don't drive it wide open all the time, but I don't drive like a grandma either.


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