I have a 6 speed too, but it's a C5.
No mods, I can go from Vegas to LA and back doing 30 mpg. And that's with HUGE mountains we have to climb, air conditioner, and at around 85 mph. I do around 21 mpg around town with combined city/highway driving.

After cam & bolt ons, around 27 mpg to LA & Back. 17 mpg around town. Mostly my fault, can't resist punching the car <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Just got stage 2 heads 4 days ago. Didn't go to LA yet. And I have changed jobs where I don't drive highway as much. My mpg has gone down to 14 mpg in the last 4 days. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> My foot keeps on stepping the throttle to the floor for no reason <img border="0" alt="[evil]" title="" src="graemlins/gr_devil.gif" />

 

WHEN IM RACING AROUND I ONLY GET ABOUT 180 MILES ON A FULL TANK. If i keep my foot off the gas i can get around 240. Thats a big difference. What are you shifting at. Are U shure its not the way u drive the car??

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Biochem:
<strong> So this is about the third long trip that I've tried keeping track of my mpg. This was all highway miles, doing about 80mph the whole way (around 1800rpms), and the outside temps were near 35F and clear skies. The trip was 234 miles and took about 10 gallons of 93 octane each trip. My math, that comes to 23-24 mpg... shouldn't I be more like 28? My old 84, with a lot more HP motor and a q-jet, used to get 25mpg... I thought FI was supposed to be so much more efficient <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> BTW- the only mod so far is a lid/holley air filter and a descreened MAF. Tires are even inflated to 35psi... </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wishful thinking, be happy with what you got. I have no problem with steadily fueling a 450-500 rwhp motor which gets 10 miles per gallon highway. I am just don't have the money to build it <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> .
Regards and good luck with that 28 mpg,

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 96SCTA:
<strong> WHEN IM RACING AROUND I ONLY GET ABOUT 180 MILES ON A FULL TANK. If i keep my foot off the gas i can get around 240. Thats a big difference. What are you shifting at. Are U shure its not the way u drive the car?? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I swear to God people don't actually read threads before they reply. I laid out my scenario already on page 1. I tried to maximize my mpg on a test trip. That was a straight shot 195 miles at 72-73mph in central Illinois (that means flat as can be). The return trip a day later was 22mpg. Same conditions. 2 exit ramps, no a/c, no extra weight, 6th gear. Since then, under varying conditions, I've never gotten over 23mpg.

 

how do you expect your car to get the factor sujested fuel milage when you have made modicfications to your car????????? <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" />

 

M6 car, 30+mpg on long trips. headers, etc.

 

Ironic little twist here...

WAAAAY back, one of the top brass from FORD was driving a new mustang, a '66 I believe. It was a GT with the K-code 289, 4-speed, and 4:11 rear. The car was triple black and had a real leather interior, all custom goodies for the top dawgs. Anyways, he complained that it wasn't getting good gas milage and took it into the shop to make it more reasonable.

Well, rather than detune the car or spend the labor of installing a different gear ratio in the rear, they simply changed the speedo gear so that it said he was going faster than he actually was. This made his slow down and "increased his gas milage" like he wanted.

Just a little bit of useless info.

-Brad

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 96SCTA:
<strong> how do you expect your car to get the factor sujested fuel milage when you have made modicfications to your car????????? <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Mods? You are kidding right? An air filter should not drop the milae by 17%! lol

 

I seriously doubt there is anything wrong with your car. A few mpg is easily eaten up by driver error. 80 mph down the highway is not going to get you the best results, slow down, your gas mileage will increase. Do you live in a metropolitan area? This could also be a factor if you are running oxygenated fuel, or fuel with ethanol-burns cleaner but also burns more-ie less mpg. If you think something is wrong with it, take it to the dealer. It is your right to exercise concern, but I doubt they'll do much.
Good luck. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

I've got 400 miles on a tank on 2 different road trips which was about 25 to 26mpg.

this is in my 382 stroker with all the bolt-on's, M6 and 3.42 10-bolt. I'm pretty happy with it <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> , 457rwhp/448rwtq.
Around town I usually get around 18-19.

48000 miles now

 

it goes something like this. Car manufacturers test their cars with the most absolute perfect parameters. They will test for gas milage on perfect level roads in an area that is at the best sea level, best atmospheric pressures and at the perfect outside temp. They will also baby the crap out of cars to stretch their results. We drive the cars we own nowhere near like the manufacturers test them to be driven. You cant expect much when you arent driving the car the way it was tested. Also, there are some engines out there, that will run more efficently than other just like it. there is no ryhme or reason to it, but no matter how you look at, every situation is different.

 

what is your secret? 34 MPG, dayamm, thats awsome. Did you use cruise control? Whats your tire presure and so forth...

 

Simlar conditions...higher temps, 02 M6 cruising 80-90 and a few runs up to 135mph I averaged 28.7

I'm sure this has been mentioned, but did you check your air filter????

 

"""fuel with ethanol-burns cleaner but also burns more"""...Is this true???

Doesn't Unical 76 use ethanol in place of MTBE????

 

My 98 M6 always gets around 31 mpg on the highway at around 85mph

 

in my a4 with the heads and cam i get 24mpg highway thats only going 70

 

I think the key here is that iit was 35F out when he made this trip. In cold temps, engines gas mileage goes way down. Had it been ~ 60F, you would have gotten a few more miles per gallon.

My truck in the winter gets ~ 14.5 mpg commuting to work, whereas in the summer it will get ~17 mpg on the same trip.

 

The colder the weather, the denser the air. The denser the air, the more drag affects fuel economy. It's pretty significant.

Hotter weather has less wind drag, but if you run the a/c, it will cost you 1-2 mpgs. Ideal weather for getting the best mpg is the hottest weather you can run in with the windows rolled up and the a/c off. Lots of guys in high altitude get great gas mileage because of thinner air. Running around in the Texas panhandle is a lot better for fuel economy than running at sea level like in Houston. Something to think about.

 

I think WS6 John just hit the nail on the head. I lose about 5 mpg in ALL of my vehicles (even the V6 cars) between September and December. Once the temp drops below 40, mpg is out the window.

I'm not sure if this is right, but my theory is that colder air is denser - and the computer responds by giving more gas to burn with the O2. Acts just like you are stepping on the throttle more than you really are. This is only MY theory, but I DO KNOW that cold air gives me worse mileage.

I've also noticed that the cold air effect is MULTIPLIED by highway speed. If I drive at 65, I lose 3-4 miles per gallon. If I spend much of the trip above 75 though, I lose 5-6 or more. Cut those numbers in half at the same speeds in the summer. Go back to summer temperatures, and I get better mileage at 85 mph than I do in the winter at 65 mph.

Also, what do you have for wheels and tires? Make sure the cars you are comparing to have the same wheels - weight of your vehicle, especially at 80mph is going to play hugely in your mileage.

Another thought is to check your front end for proper alignment. If your have even one front wheel that is off by a few degrees, that can cost you a couple mpg as well.

I've also been told that the brand of oil you use in your rear end can make 1-2 mpg difference.

Check the gap on your spark plugs - my local mechanic improved my mileage by shortening the plug gap because it was a bit too far and not performing correctly on a couple of plugs in one of my cars. Just because they are factory plugs doesn't mean they are "right."

Also try doing mileage checks with the different brands of gas. I tend to get better 1-2 mpg more with Mobil gas, for example, than I do with Citgo.

Put 3-4 bottles of drygas in your full tank and run it through. I've found that with near-freezing temps, it's easy to get a bit of moisture in your tank - and THAT will also rob you of a couple mpg.

Each of these little things might be robbing you of a mpg or two, together they easily add up to the difference between your results and what SOME others have gotten.

I think some people here just have enough money that they are buying big HP cars and don't care about mileage. Great for them. Others are used to the big old V8 pre-LS1 cars that got terrible mileage. I for one am looking for that fine balance between power and affordability. I'm hoping I can get at least 24 mpg on a trip with my 6 speed LS2 402 when it is done. People who don't "worry" about mileage aren't realizing how many hundreds of dollars per year they are wasting, that COULD be spent on more important things.......... like more mods.

 

I remember when I took a trip to Dallas from the RGV (about a 10 hour trip), I averaged about 29mpg. On the way back home, I averaged about 30mpg (after being tuned). This was with a cam, LT's, exhaust, lid and throttle body stock gearing.