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Discussion Starter · #1 ·
The roads were dry so I thought I'd use the M6 to take a weekend drive. Checked the mileage on the 180 mile drive from Marshfield to Iron River Wisconsin. It was 13 degrees when I left Marshfield and 19 when I got to Iron River 181 miles later. 21.3 MPG on a 2-lane highway with 14 small towns in between. Same trip and about the same temperatures back & got 21.5. I'm sure it will do better in warmer temps. Anybody else getting these mileage results? My car is a 6-speed with secondary cats, H-pipe, & resonators removed with an X-pipe installed. Removed the carbon filters and added the RPI scoops, block-off plates & BMC filters.
 

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The roads were dry so I thought I'd use the M6 to take a weekend drive. Checked the mileage on the 180 mile drive from Marshfield to Iron River Wisconsin. It was 13 degrees when I left Marshfield and 19 when I got to Iron River 181 miles later. 21.3 MPG on a 2-lane highway with 14 small towns in between. Same trip and about the same temperatures back & got 21.5. I'm sure it will do better in warmer temps. Anybody else getting these mileage results? My car is a 6-speed with secondary cats, H-pipe, & resonators removed with an X-pipe installed. Removed the carbon filters and added the RPI scoops, block-off plates & BMC filters.
I have been able to get that on a long trip when I was light on the throttle and short shifting at 3k rpm's. Then I decided it was too boring and started shifting again at 8k RPM and had to fill up every 30 minutes cherrsagai
 

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Best I have ever done is 18-18.5 mpg on the heavily patrolled I-45 between Dallas and Houston, cruising between 75-80 mph. It was cold (for TX) at 35 degrees that day. On the way back I got in with some other fast moving traffic and my mileage reflected that. I'm not overly concerned with the mileage but it does become a bit of a game to play on long drives on roads that have a lot of cops to see how many mpg I can get. Oddly enough, my wife's Escalade gets better mileage on the "Houston Run" than the M6 does--we regularly get 20-21 out of it--not bad for a 403 hp, 6000 pound SUV.
 

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Best I have ever done is 18-18.5 mpg on the heavily patrolled I-45 between Dallas and Houston, cruising between 75-80 mph. It was cold (for TX) at 35 degrees that day. On the way back I got in with some other fast moving traffic and my mileage reflected that. I'm not overly concerned with the mileage but it does become a bit of a game to play on long drives on roads that have a lot of cops to see how many mpg I can get. Oddly enough, my wife's Escalade gets better mileage on the "Houston Run" than the M6 does--we regularly get 20-21 out of it--not bad for a 403 hp, 6000 pound SUV.
I've driven the I-45 route between Houston and Dallas (Las Colinas) quite a bit when I lived in Texas. It has to be one of the most heavily patrolled highways in the country. Hats off to you...I don't know if I have the discipline to drive it in my beast. The best mileage I've managed is 16.5 on a short highway run. During my normal 17 mile trip to drop my daughter at school, I average about 11.8 mpg. I am currently on the march to the basement with 10.2 and declining due to heavy traffic this week.
 

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Cruise control is the only way I can do it. Without the cruise I find myself traveling at speeds more commonly associated with aircraft.
 
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Cruise control is the only way I can do it. Without the cruise I find myself traveling at speeds more commonly associated with aircraft.
That is my experience, as well!:wroom:
 

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I'm sure it will do better in warmer temps.
Cold air holds more oxygen than warm air, and should result in higher mileage. The only thing Ajax can think of to get your mileage down to an acceptable level (9 - 10MPG) is a more aggressive driving style, and redlining it at each gear.
 
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Cold air is also more dense and harder to move an object such as a fast moving M6 through. Then again, a gallon of fuel is denser at lower temps...all these variables are making my brain hurt! My hypothesis would be that the increased aerodynamic drag would be the dominant factor--would be an interesting experiment.
 

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Discussion Starter · #9 ·
Yeah, cold air would help with a colder intake charge but the cold weather increases drag on all moving parts too. Bearings, U-joints, etc aren't as easily moved with low temps thus more resistance. Here's some info from why cold weather mileage drops;

So, why exactly does colder weather throw a wrench at most vehicles’ regular fuel economy? Well, there are lots of reasons actually, but friction is a big one. While it's always an issue, cold weather increases friction on almost every front. Most vehicle fluids, from motor oil and transmission fluid to power steering fluid and differential gear oil, are thicker and more resistant to flowing when cold. Translation: Harder to pump, more work for the engine. Another less obvious source of friction is rolling resistance.

First of all, cold temperatures lower the pressure in your vehicle’s tires by 1 to 2 PSI for every 10 degrees that the temperature plummets. Secondly, when the weather turns foul, vehicles must work harder to push through snow and slush. Both of these conditions equal greater rolling resistance and more fuel used to cover the same distance. Add to that the fact that gasoline doesn’t atomize and burn as well in cold temperatures; trace amounts of unburned fuel are left in the cylinder and evacuated with the exhaust. Yes, it’s a double-whammy. Not only does that unburned fuel equal lost power, it also substantially increases your vehicle’s emissions. But that’s not all—throw in heavy use of the heater, winter gas formulations and short trips to and fro, and it’s a recipe for pain at the pump.

What’s Happening under that Hood

All vehicles have an optimum operating temperature, and the colder it is, the longer it takes to get there. While modern engines make very efficient use of the fuel mixture entering the engine, they rely upon the oxygen sensor to monitor the O2 content of the exhaust, as well as sensors for manifold pressure, mass air flow, throttle position, and coolant temperature, among others. All of this information is communicated to the vehicle’s computer that continually adjusts ignition and valve timing as well as fuel injector pulse width, to fine tune the amount of fuel delivered to each cylinder. This is done many times per second. But here’s the caveat—this engine-management system is only at tip-top efficiency when the engine is at full operating temperature. And when the mercury’s showing low, all vehicles require longer periods of time to reach that full operating temperature—and it’s in that warm-up period that efficiency is lost.

Add to that the common practice of making short trips (to minimize running to and fro in sub-zero temps and wind chills), and each time your vehicle cools down it has to come back up to optimal operating temperature. It all takes its toll.
 

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There my brain just exploded. Damn, I need it for later.
 

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Cold air holds more oxygen than warm air, and should result in higher mileage. The only thing Ajax can think of to get your mileage down to an acceptable level (9 - 10MPG) is a more aggressive driving style, and redlining it at each gear.
I'm almost there! MPG stands at 10.2 as I exited the car 15 minutes ago. My good work will be somewhat foiled by a 12 mile interstate trip in the rain. I anticipate nailing the goal before Friday. :cheers:
 

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Ajax seriously doubts that the drag coefficient of air at temperatures in the 20°F range would have much effect on a pretty-well aerodynamically designed vehicle at highway speeds. It's not exactly an F1 race. Plus, when it's cool, you get a lot less impact resistance from flying mosquitoes and June bugs-- a factor too often overlooked in scientific analysis.
 
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Aircraft take off in shorter distances in cold weather, so at the speeds we normally drive at, the increased power more than offsets the increased drag. However at less than full throttle, the aforementioned friction issues may come into play when the car is cold (but I suspect are not in play when the car is warmed up). Just a guess on my part...

At most race tracks, the lap times increase when the track becomes hotter for what that is worth.
 

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Has anyone been able to calculate the dramatic drag coefficient difference when you have your wife in the passenger seat? I know MINE creates some serious reduction numbers.....:nono:
 
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Has anyone been able to calculate the dramatic drag coefficient difference when you have your wife in the passenger seat? I know MINE creates some serious reduction numbers.....:nono:
I just have a decrease in the fun coefficient. It is like having my own private LEO in the car. :cop: Keep in mind, however, she drives her 5 like a bat out hell! I really think that it is the exhaust note! I was once asked how to make the car quieter...I just pulled into the neutral ground and turned it off!! :1:
 
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I don't get much of a drag increase but do notice a persistent whining sound on some occasions from what sounds like the right side of the car when subjected to high lateral or longitudinal g-forces....strangely the rear seat on the Escalade produces the same exact sound .
 

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Brings to mind that old joke: Did you hear about that new muffler for your car? Makes it 50% quieter! Fits right over her mouth.

I keep hearing "Do you drive like this all the time?" when she is in the car. Of course I swear (lie) that I don't.
 

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You did pretty well on the gas mileage. Temperatures really make a difference, thats for sure. Houston weather never gets cold enough to tell a difference (especially with traffic)
 
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