when i first bought this car i was fairly disappointed with the mileage. but when the canadian winter came my mind was made up to keep this 4wd fun little sedan. now back in summer time my car doesnt have much advantage over the regular FWD sedans so the cost of gas was bothering me again. my subaru likes to chug more gas in summer time and produces less power. specially with AC on i can no longer pulse at a reasonable pace below 1500rpm as the engine loads out. in cold weather i had a lot more reserve power and no need for AC and my car warmed up reasonably quick.
anyway this past month i bought new tires with aggressive tread pattern for less friction. i also changed all my differential and transmission fluids with synthetics. my engine oil is still fairly fresh with 2000 miles (rotella t6 5w40) but when its time comes it will be swapped for 0w20. Since i drive mostly rush hour i was getting 20-22mpg only. So i started to work on driving without brakes, which you all know is all about anticipation. that gave me couple MPGs and brought me up to 24mpg. after that i started working on better managment of throttle. Now I applied throttle in pulses and glided for however long necessary at closed throttle in traffic. i made sure to glide at least 3 seconds for every second of acceleration. all my acceleration runs were now done at low rpms of around 1000-1800. anything above 2000rpm and my car starts burning that gas. Even though subaru engineers claim BSFC sweet spot of 1500-4000rpm at near full throttle. this is simply not so as the real world figures are around 80% power at 1500-2000rpm. i compiled a map of my pulse and guide results that i testes. at the end of a the test run for the specified rpm and torque i gave anything above 28mpg a green dot, 27 mpg yellow, 26mpg orange and 25 and below red. i didnt manage to test the whole map.
This might have to do with the valve lift that occurs at higher engine speeds because fuel mixture stays stoich. whatever the cause after several pulse and glide tests i found that higher RPMs did bad things to my mileage. my testing methods were in no way scientific either. In any case my accelerations were at about 35-45hp range according to scangauge (that's roughly 1/4 of peak power compared to subarus claim of 1/2 for best BSFC). on uphills if my speeds started to fall below the limit i would briefly accelerate at 2500rpm and 1/2 throttle which was about 60-70hp. But i applied generally enough throttle on uphills so as to not lose too much speed and momentum and i coasted the downhill in DFCO. hills are actually pretty good for you.
overall i found that its all about the throttle control - not how much you press it but how increasingly you do so. The subaru ECU takes throttle's rate of change into consideration in locking and unlocking the torque converter. so by slowly opening the throttle i manged to accelerate with a locked torque converter in 3rd and above gears.
i also dont try and exceed 40mph, its above that speed that my mileage dips dramatically perhaps due to the all wheel drive. 35mph puts me in overdrive gear and at 1300rpm cruising range. again this doesnt make any sense in comparison to the subaru bsfc map:
my speed vs mpg tests for cruising
overall im happy with the new 28mpg result at average speed of 29mph. its mostly rush hour traffic. im hoping with better oil and broken in tires i can hit 30mpg. thats a tall order though considering that i get 30mpg on the highway at about 70mph. I will be posting pics and info as i go on.
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