[widetrak]

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

 

[rock421]

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.

 

[George8211]

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

 

[rock421]

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

 

[George8211]

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

 

[muohio]

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.

 

[rickglow]

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.

 

[Luth]

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...

 

[kevracer]

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.

 

[lisatw151]

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.

 

[capra2d]

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.

 

[NEW2GTO]

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.

 

[Afterglow]

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.

 

[GTO TOO]

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 !!!!!!

 

[GT MECH ENG]

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?

 

[JTYLER1604]

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

 

[JMVorbeck]

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.

 

[diverdan]

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.

 

[GT MECH ENG]

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"?

 

[GT MECH ENG]

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.