Poor Fuel Mileage - Pontiac GTO Forum
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post #1 of 23 (permalink) Old 10-14-2005, 06:59 AM Thread Starter
 
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Poor Fuel Mileage

Does anyone have any ideas as to why the GTO gets the gas mileage that it does? On the highway I am getting about 22 mpg. My '02 vette gets 31 mpg. What is the rearend ratio in a GTO. I know that the GTO is pushing more air, but 9 mpg difference between the two cars seems like a lot. What is the GTO's coefficient of drag? By the way, around town mileage is horrible (about 13 mpg)....but the weight of the car and my driving habits can probably explain that.
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post #2 of 23 (permalink) Old 10-14-2005, 07:26 AM
 
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I'm in the same boat man. Went from a 98 Vette which I got 16.5 in town driving, now i'm at 12mpg. I'm hoping it gets better once the engine is broke in. It is geared lower that the C5 at 65 in the Vette I was at 1250rpm, at 65 in sixth gear in the GTO its closer to 1500rpm. .
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post #3 of 23 (permalink) Old 10-14-2005, 09:53 AM
 
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If you had an auto C5, the gear ratio was 2.73 rears or if you had the performance rear it was 3.15. Now you have a 3.46 rear. Stick versus stick the rear is the same, the tranny is slightly different. That would explain a small amount of difference. I'm not sure why the GTO gets such bad mileage. My 02 Z28 with an A4 and 3.08 gears with 335 RWHP got 29-30 on the highway and 19 in town. My Z06 C5 got 18 in town and 26-27 on the highway. The GTO is getting 17 city and 22-24 highway with the same type of driving. I think the weight has something to do with it, but that can't explain all of it. The CD is good for the GTO and matches the C5, but the GTO does have more frontal area. Still it shouldn't be such a large difference IMO. Oh well, I didn't buy the car for mileage, so I can live with it I guess.
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post #4 of 23 (permalink) Old 10-14-2005, 11:07 AM
 
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Same here. Went from a 01 C5 6spd getting 20 city and 30+ highway with a 3.42 rearend to 17 city and 22 highway in the A4 Goat.

Higher frwy rpm, more weight, more drag and a shorter overdrive gear sux all the fuel.
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post #5 of 23 (permalink) Old 10-14-2005, 11:39 AM Thread Starter
 
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So, changing the rear gear to a 3:08 and then installing different 1-3 gears in the transmission will allow similar lowend acceleration but provide better 4th gear fuel economy?
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post #6 of 23 (permalink) Old 10-14-2005, 11:45 AM
 
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I probably have more seat time in the GTO than just about anyone in the US, and I can say without question that it's the around-town / slow traffic driving that kills the average mpg in these cars....I blame the work required to get two-tons of metal and glass moving...taking some care and shifting efficiently helps a lot. This car is fun to yank thru the gears, however, so that is exceedingly tough to do.

I seriously doubt dinking with the tall gear ratios will help much.

I have seen posts where some people claim 29 mpg averages...of course, some people claim they've seen Bigfoot as well.
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post #7 of 23 (permalink) Old 10-14-2005, 12:15 PM
 
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19 - 21 mpg

I commute 108 miles per day and a good 30 of that is in stop and go traffic. Avg speed for a tank of gas is 39mph and depending on how much I endulge when not in the bumper to bumper stuff, and I get 19 to 21mpg per tank. I took a road trip from Pleasanton CA to Pasadena CA, 350 miles, and did get 29mpg. I agree with Groucho, the stop and go really kills the mileage.
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post #8 of 23 (permalink) Old 10-14-2005, 08:38 PM
 
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Mine is two weeks old now and is getting 20 mpg average. I'm quite happy with that........



JET
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post #9 of 23 (permalink) Old 10-15-2005, 10:07 PM
 
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Just took an 800 mile trip. I found that if I set the cruise at 70 and turn the Valentine off (it just forces me to go) I get 25 mpg. At my normal 80-90 cruise I get 23. But about 250 miles of this trip was rural hwy with 55 mph speeds. I kept the cruise at 62 and was amazed to get 28.5 mpg. The computer showed 27.9 for that leg, but when I actually calculated it, 28.5 is what it was.
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post #10 of 23 (permalink) Old 10-16-2005, 03:39 PM
 
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Mine is 1 week old and is getting 12 mpg. Its an improvement for me over my 2500 Subn. so I really dont mind it at all.

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