This last weekend I went on a road trip up near Cleveland Ohio to visit all of my family. I've been trying to conserve some money as I need tires soon and decided to do a little fuel economy test... This is on a 2009 STi. What I think I figured out is that at around 2750 RPM's the car's fuel economy starts to drop drastically. this is around 67mph. I found a nice little sweet spot where the car wasn't working hard at all to get up the hills through tennessee/kentucky. This was around 65mph even.... So the question is, is it worth it? Here's my results: (using receipts, not the in car MPG gauge...which was actually damn close) Overall: Distance: 1300 miles (round trip) Fuel Used: 46.429 gal MPG: 28.0 Best MPG: 28.7 (for one tank) Avg Price: $3 even (friggin 3.08 a gallon when i had to fill up in ohio...) Total Cost: $139.29 Time: 11hr 30min (1 way) my last trip up there in June was: Distance: 1300 miles (round trip) Fuel Used: 61.905 gal MPG: 21.0 Avg Price: $3 even (to make the comparison) Total Cost: $185.72 Time: 8hr 59min (1 way) Savings were: $46.43 And it was 95% less stressful because I didn't have to worry about a speeding ticket at all. It's a little awkward going 65-67mph in a 70mph zone... So was it worth it? And 28.0 is a pretty damn good number, can anyone beat that? Edit: Forgot to mention when i was trying to avg 70-75mph with light acceleration I was getting in the 22 MPG range
Cool. But as mentioned 2 1/2 more hrs of driving? That's quite a bit more time. What's weird is the humongous drop with fairly no load. Are you tuned any at all? Optimization of the Maf scaling is key here. The Subaru's factory Maf scaling is horrendous. I've done a factory tune on my old Subaru and no only did it make more power.....gas mileage upped tremendously. My M3 is a different animal. I find it's sweet mileage spot is higher up in the revs. I got better mileage going 80-82 mph vs 74-76 mph on my trips up to NY. I'm talking 28-30 mpg vs 19-21. This is like the total opposite but again these are two different cars and two VERY different ECU's (or in Bimmer terms DME).
well i was tired as is, so 2 1/2 hours of relaxing on the couch would be the only time lost. Although, like i said with the less stress I did feel less tired, might have added on 2 hours to my life...canceled out the bad habits slightly. it was worth it this time as I'm trying to save up for the tires. the 245/40/18's are a bit more pricey. as for the time i went up in june, nope wouldn't be worth it. i'm not tuned, i have played with the computer lightly while learning. the car only had 3k miles in march, up to 20k as of that trip. so still light miles. besides MAF i imagine not much would have affected the fuel economy as it just stayed at 2500-2750 rpm's for about 5 hours straight at a time.
Props to you man. I can't do long trips anywhere close to posted speed limit. Getting to point A to B quickly as possible is my main concern lol.
Going to try 68-72 Thursday for the same trip to prove if the difference really is that large in that small of a mph difference. If I get halfway and it's only 21-22 I figure I'll just kick it back up to cruising speed the 2nd half
those are nice numbers on my drive from philly to atl, i got about 31mpg in my 08 on a perrin tune. this was going at the same speed you stated ~67mph
I only drive hwy miles now and Ive seen my MPG (based on calculations done at the pump) range from 16 to 27mpg. If this is something you're curious in, you need long term data to see if theres any sort of trends associated. And by long term, I mean at least 3 months...call it a quarterly analysis. Input the data into excel, along with a column that indicates average speed (if you can account for that) and plot that biotch into a couple different graphs every quarter to see whats going on
yes. I do take into account the tennessee/kentucky stages vs ohio. Although, it evened out well due to the just coasting completely down hills. Not sure if I'm patient enough to do quarterly logging. Plus my last road trip I averaged 14mpg after 565miles. At one point it showed 8mpg at 60miles on the clock...
I found the same thing with my 08 STI. Once you crack 70mph the fuel economy drops a lot. I noted 1-2mpg between running 70 and running 75. I tend to run between 65-70 and I average 22-23mpg in mixed driving. I have not had a chance to do a long all highway road trip.