n2oiroc Posted February 4, 2017 Share Posted February 4, 2017 ^no it doesn't you are BARELY above 2K at 70.... rpm and load are 2 different things. Link to comment Share on other sites More sharing options...
n2oiroc Posted February 4, 2017 Share Posted February 4, 2017 Owned a 2015 WRX CVT, and now the 2.5 Legacy, and tracked fuel use since new using Gas Cubby (now Fuelly). At no time did the WRX get better mpg's in the same driving as my Legacy, (I didn't and don't hypermile, I just drive/drove them, mainly back and forth to work and long highway trips every few months). Not sure what the difference is for you. I will say if you are banging out great MPG's with a WRX you must be avoiding boost (a lot) and that is a sad way to use the main attraction of a WRX. (also, after a year+ with WRX and now 6 months with Legacy, I am sure I made the right choice for me trading) cvt wrx's are known pigs on fuel. 6 speed wrx's get better mileage. and i hit peak boost many times per day. the issue is the 2.5 legacy is at 30% load to maintain 80 mph and the wrx is at 15% load. made up #'s, but the point still stands. if you have ever looked at the fueling map on an ecu you would know what im talking about. an engine will use less fuel at 4,000 rpm and light load than it will at 2,000 rpm and mild load. Link to comment Share on other sites More sharing options...
ammcinnis Posted February 5, 2017 Share Posted February 5, 2017 The 4 cyl is just too uderpowered and has to work too hard at 70+ mph ... You have to drive absurdly conservative to get reasonable mileage out of a 2.5 outback/legacy. That's simply not true. http://badges.fuelly.com/images/sig-us/311503.pnghttp://badges.fuelly.com/images/sig-us/424498.png FWIW, a 6th Gen Legacy cruising down the highway at 70 mph under no-wind conditions requires less than 30 horsepower. The 175 hp H4 engine is hardly "underpowered" or "working too hard" under those conditions. an engine will use less fuel at 4,000 rpm and light load than it will at 2,000 rpm and mild load. Wrong ... except in unusual circumstances. And such a statement is absolutely meaningless unless you quantify "light load" and "mild load." For any given power requirement, there are an infinite number of combinations of rpm and torque (~throttle opening) that will satisfy that requirement ... but only a narrow range of values will yield the highest efficiency. In general, for a given horsepower requirement efficiency usually favors lower rpm (above some threshold) and higher throttle openings. "If you don't know where you're going, any road will take you there." ~ The Cheshire Cat (Alice in Wonderland) Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 That's simply not true. http://badges.fuelly.com/images/sig-us/311503.pnghttp://badges.fuelly.com/images/sig-us/424498.png Wrong ... except in unusual circumstances. And such a statement is absolutely meaningless unless you quantify "light load" and "mild load." For any given power requirement, there are an infinite number of combinations of rpm and torque (~throttle opening) that will satisfy that requirement ... but only a narrow range of values will yield the highest efficiency. In general, for a given horsepower requirement efficiency usually favors lower rpm (above some threshold) and higher throttle openings. How much tuning and engine management experienced you have? Most base fuel maps look somewhat like this. You can run at a higher rpm and use less fuel very easily than running at a lower rpm and higher load. http://i153.photobucket.com/albums/s201/n2oiroc/7F3FE144-A313-41F5-AEA9-DB5D0666C2AE_zpsetxm6t8n.png Link to comment Share on other sites More sharing options...
ammcinnis Posted February 5, 2017 Share Posted February 5, 2017 How much tuning and engine management experienced you have? My 50+ year experience is limited to normally-aspirated motorcycle, automobile, and aircraft engines. Most base fuel maps look somewhat like this. You can run at a higher rpm and use less fuel very easily than running at a lower rpm and higher load.Show me a plot of BSFC vs. RPM. "If you don't know where you're going, any road will take you there." ~ The Cheshire Cat (Alice in Wonderland) Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 My 50+ year experience is limited to normally-aspirated motorcycle, automobile, and aircraft engines. Show me the BSFC vs. RPM curve. Thats a meaningless measure, especially without vacuum or some ofher form of load. Injector duty cucle vs load and rpm is what will show fuel consilumption. If you have some sort of secret on how i can get better mileage out of this thing without slowing down, il all ears. Link to comment Share on other sites More sharing options...
dgoodhue Posted February 5, 2017 Share Posted February 5, 2017 At 4000 rpm, the engine is firing twice as often as 2000rpm.So it would were in the blue range 60-70 at 2000rpm, it would be using less fuel than purple range 40-50. I do understand what you are trying to explain though. If you're driving 2.5i to attempt to keep up with your WRX I can see your fuel economy being worse in the 2.5i. Top gear did an episode where they drove a Prius all out and it got worse fuel economy than a M3 that kept pace. Link to comment Share on other sites More sharing options...
dgoodhue Posted February 5, 2017 Share Posted February 5, 2017 If you have some sort of secret on how i can get better mileage out of this thing without slowing down. How fast are you driving? Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 How fast are you driving? My highway driving is at 80 or so. I do drive some 45-65 roads and even on those i cant touch 30 mpg. Ive been really close to epa estimates on every car ive owned but this one. Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 At 4000 rpm, the engine is firing twice as often as 2000rpm.So it would were in the blue range 60-70 at 2000rpm, it would be using less fuel than purple range 40-50. I do understand what you are trying to explain though. If you're driving 2.5i to attempt to keep up with your WRX I can see your fuel economy being worse in the 2.5i. Top gear did an episode where they drove a Prius all out and it got worse fuel economy than a M3 that kept pace. Thats pretty much my whole point. If you do anything but baby this thing its a pig on gas. I use the throttle the same on this as i do my wrx. I dont get in the legacy and floor it and then hop in the wrx and baby it. Both of them get the pedal buried daily. Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 Fuelly is a good example. They have the 2016 2.5 legacy at 27.5 and the 2016 wrx at 24. The legacy is rated 8 mpg higher and the average legacy driver is far more conservative than the average wrx driver. They have the car setup to nail the epa test but it fails miserably under real world driving. Link to comment Share on other sites More sharing options...
Mark N Posted February 5, 2017 Author Share Posted February 5, 2017 Mark N: does your your 16 Legacy with the 6 cylinder have a CVT Tranny?Yes, it does. Link to comment Share on other sites More sharing options...
ammcinnis Posted February 5, 2017 Share Posted February 5, 2017 Thats a meaningless measure, especially without vacuum or some ofher form of load. Rave on, Dude! If you have some sort of secret on how i can get better mileage out of this thing without slowing down, il all ears.Maybe if you stopped driving your Legacy down the highway at 4000 rpm ... "If you don't know where you're going, any road will take you there." ~ The Cheshire Cat (Alice in Wonderland) Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 Rave on, Dude! Maybe if you stopped driving down the highway at 4000 rpm ... Its nowhere near 4,000 rpm. Am i supposed to drag ass down the freeway because subaru cant figure out how to get decent mileage at routine legal speed? Link to comment Share on other sites More sharing options...
upstater Posted February 5, 2017 Share Posted February 5, 2017 The Legacy is set up to nail the EPA test, but fails miserably when you drive the piss out of it (including 80mph on the highway, weird how driving it well out of the EPA tested speed reduces mpgs?). I'm just gonna venture to say you can have mpg's if you drive less aggressively, but since it isn't your goal, probably shouldn't complain about it. Any other gasoline vehicle will likely disappoint you. Maybe try Electric next? PS: since you like charts, see if you can find how long during the High Speed (8 mile) EPA Highway test the car is running above 75mph (about 20 seconds), and then average that in with the normal Highway test which is over 10 miles sub 60mph: https://www.fueleconomy.gov/feg/fe_test_schedules.shtml So they test Highway MPG's with over 18 miles of driving on a dynamometer (and do one additional test sub 60mph with A/C running), during which 20 seconds is spent at speeds 80 or higher. The average speeds of the Highway tests are sub 50mph... No wonder you can't get EPA MPG estimates when you drive it at 80mph. Science is a cruel mistress. So choose, EPA numbers, or speed, because you can't have both. You can jump up to the 3.6, so your engine isn't working as hard as the 2.5, but that won't give you better MPG's than you have now for your drive (those numbers were already posted on the first page of this thread, go to Fuelly and compare the two engines, with over 2 million miles reported since 2015) Next Gen Legacy might have Direct Injection, and offer slightly higher MPG's, might also drop the 3.6 in favor of the 2.0 DIT, since they already have that engine worked out. But then you have to worry a bit about longevity, even with a 2.5 NA DI you need to keep the valves clean or MPG's over time will drop...which will just be another thing to complain about. Electric is where it is at, once they figure out the whole battery/cruising range thing. But then again, wind resistance increases exponentially as speed increases, so then you will be on the electric Legacy forum complaining that you cannot get the range out of your batteries that the EPA tests shows you should be getting...Groundhog Day! Link to comment Share on other sites More sharing options...
n2oiroc Posted February 5, 2017 Share Posted February 5, 2017 The Legacy is set up to nail the EPA test, but fails miserably when you drive the piss out of it (including 80mph on the highway, weird how driving it well out of the EPA tested speed reduces mpgs?). I'm just gonna venture to say you can have mpg's if you drive less aggressively, but since it isn't your goal, probably shouldn't complain about it. Any other gasoline vehicle will likely disappoint you. Maybe try Electric next? PS: since you like charts, see if you can find how long during the High Speed (8 mile) EPA Highway test the car is running above 75mph: https://www.fueleconomy.gov/feg/fe_test_schedules.shtml And then average that in with the normal Highway test which is over 10 miles sub 60mph: https://www.fueleconomy.gov/feg/fe_test_schedules.shtml Then choose, EPA numbers, or speed, because you can't have both. You can jump up to the 3.6, so your engine isn't working as hard as the 2.5, but that won't give you better MPG's than you have now for your drive (those numbers were already posted on the first page of this thread, go to Fuelly and compare the two engines, with over 2 million miles reported since 2015) Next Gen Legacy might have Direct Injection, and offer slightly higher MPG's, might also drop the 3.6 in favor of the 2.0 DIT, since they already have that engine worked out. But then you have to worry a bit about longevity, even with a 2.5 NA DI you need to keep the valves clean or MPG's over time will drop...which will just be another thing to complain about. Electric is where it is at, once they figure out the whole battery/cruising range thing. But then again, wind resistance increases exponentially as speed increases, so then you will be on the electric Legacy forum complaining that you cannot get the range out of your batteries that the EPA tests shows you should be getting...Groundhog Day! Ive never complained about mileage in any other vehicle ive owned. Ive driven them all the same and they all were close to the epa estimate when you took into account my driving style. The fact that fuelly shows the legacy almost 9 mpg lower than the epa estimate just shows how inaccurate the epa estimate is. What other car is that far off? Anyways, the 4,000 rpm comment got me curious. At 85 mph the car maintains 2,500 rpm cruising, not coasting. 2,500 rpm certainly isnt high or unreasonable by any standard. My current wrx is over 3,000 and my old one was probably 3,500 rpm and both got better mileage. http://i153.photobucket.com/albums/s201/n2oiroc/33A7B6A1-3D63-4FC0-8BE3-E131FB011A0E_zpsddic5y7c.jpg Link to comment Share on other sites More sharing options...
brandon.mol Posted February 5, 2017 Share Posted February 5, 2017 Turbo motors are more fuel efficient under load than NA motors, because greater volumetric efficiency. The slope of the fuel efficiency vs speed chart is usually flatter for with motors where the peak torque is near the cruising RPM range, because that's where the engine (not the car) is ALWAYS most efficient. For example, when you even half throttle a Prius, the engine revs to peak TQ RPM, WOT, and stays there, using the CVT to adjust wheel speed and generator to capture excess output. At 2500 RPM, if you go to gently pass or climb a hill, the 6 uses very little excess fuel while the 4 will go WOT, probably into open loop. RPM is irrelevant in fuel economy. It's all about how much fuel is going in and that's a function of your right foot only. For example, in my '12 GT, I would get better fuel efficiency in 5th gear at 60mph than 6th gear since that engine/tune is so much more efficient at 2600ish RPM than 2000ish RPM and requires LESS air/fuel. Also I get better mileage at 70mph in 6th that at 60 in 6th, same reason despite higher drag. Different engine/car I know, but in the CVT it would all come down to trans tuning. At 2500 RPM, I'd bet the FB25 doesn't make much more than 30 - 40whp, without going into open loop. <--- Guessing... Anyone ever dyno one? Link to comment Share on other sites More sharing options...
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