Frougy Posted June 6, 2013 Share Posted June 6, 2013 I have a 96 outback legacy with 145k miles. It says to use premium fuel. The 2.5 liter engine is designed to operate using premium unleaded fuel with an octane rating of 91 AKI or higher. Regular unleaded fuel with an octane rating of 87 AKI may be used if necessary. For optimum engine performance and driveability, it is recommended that you use premium grade fuel. so my question is can I use regular gas? Premium gas is $4.80/gallon while $4.40/gallon. My outback gets 23mpg. Link to comment Share on other sites More sharing options...
Kennyfvholla Posted June 6, 2013 Share Posted June 6, 2013 If you use regular gas, you will start to here pinging from the motor. I know this, and so do a few others, from personal experience. These motors do not run safely on lower octane fuel. The combustion chamber and piston design are the reaso that motor needs to run on 91 or better. If you run less, the ignition timing is changed in order to compensate, but it can only alter physically to a certain point. The threshold of where pre-detonation occurs is outside the limits of the retarded timing. Running 89, the motor seems to compensate enough, but you loose power and efficiency to the point where fuel mileage is affected and you're better off running premium. Trust me, it's not worth the trouble. Just run 91 or better. Running 87 temporarily "IF NEEDED" because for some reason you can't put anything else in it and are going to add higher octane fuel later on, won't hurt anything. But in the long run it's just not worth it. You'll see 15/16 MPG around town running 87. Link to comment Share on other sites More sharing options...
Sludgeroo Posted June 6, 2013 Share Posted June 6, 2013 Is this only the 25d? Or does this apply to the 222 as well? I don't have the manual :/ Link to comment Share on other sites More sharing options...
Tr00b Posted June 6, 2013 Share Posted June 6, 2013 My car hates anything besides premium. I have the phase 2 engine Link to comment Share on other sites More sharing options...
pleaidestar Posted June 6, 2013 Share Posted June 6, 2013 I just brought this up a few days ago when i spaced out and put 86 in after running 89 since i did the motor swap. I just refilled with 91 this morning on the way to work, its a completely different car with low grade fuel. I have the 22e w/4eat, gas mileage is already taken away with the auto tranny and if you have one of those you know how long it takes to go into a passing gear...well with low grade fuel I thought my car was going to stall, the rpm drop was sick and It took a good second to catch up to itself. So I would say that every ej motor suffers under low grade fuel, the 30 cent difference between 86-91 is not a lot if you hate restraint and boggy driving conditions. Oh and kenny the pinging went away for the most part after I put the correct grade fuel in there, still exists faintly between 2000-2800 rpm, I did delete the egr on my car so I'm thinking combustion temps might be high since the weather has been sunny and 98° constantly for a week or so...don't know much about the egr but what I hear is I may experience some pinging because of the delete. Any truth to it? Link to comment Share on other sites More sharing options...
Zues Marine Posted June 6, 2013 Share Posted June 6, 2013 i have never used anything higher than 87(lowest at most stations around here) on the MT EJ25, with a 20°-45° timing advance averaging 30.1MPG with evenly split freeway/city driving i wonder what running 89 or 91 would do Link to comment Share on other sites More sharing options...
pleaidestar Posted June 6, 2013 Share Posted June 6, 2013 I have never since I owned the car put premium gas in it always went with mid grade fuel, I feel the difference in it, the 22e likes it. I bet the efficiency will be better going through the gears and freeway driving was better than normal for me. I will be happily putting premium In there. msd mod and 91 octane premium fuel good for 30 Awhp Link to comment Share on other sites More sharing options...
Kennyfvholla Posted June 6, 2013 Share Posted June 6, 2013 Well, my entire post is regarding the 25D from ONLY 1996. It does NOT refer to the 97-99 25D. Frougy has a 96 25D motor in his 96 Outback. Link to comment Share on other sites More sharing options...
pleaidestar Posted June 6, 2013 Share Posted June 6, 2013 The regular fuel around here is 86 octane quite crappy I don't even want to run my lawn equipment with it. I guess its a geographical or economical thing with fuel grade and regions where they differ. The city I live in is low paying job market low cost of living and just low. 800,000 people here though..weird. Link to comment Share on other sites More sharing options...
Zues Marine Posted June 6, 2013 Share Posted June 6, 2013 i guess i was talking about a '98 EJ25D Link to comment Share on other sites More sharing options...
PorkchopSandwiches Posted June 6, 2013 Share Posted June 6, 2013 Well, my entire post is regarding the 25D from ONLY 1996. It does NOT refer to the 97-99 25D. Frougy has a 96 25D motor in his 96 Outback. What's the difference between the two engines that makes premium so important? I've only ever used regular fuel in my 98 25D and I've never had a problem with detonation, even on my trip across the mountain pass with my car loaded to the ceiling with my stuff from college. If I remember right, the owners manual in the 98 doesn't recommend high octane. Link to comment Share on other sites More sharing options...
Kennyfvholla Posted June 6, 2013 Share Posted June 6, 2013 What's the difference between the two engines that makes premium so important? I've only ever used regular fuel in my 98 25D and I've never had a problem with detonation, even on my trip across the mountain pass with my car loaded to the ceiling with my stuff from college. If I remember right, the owners manual in the 98 doesn't recommend high octane. Again, it's only the 96 motor where premium is required. In the manual and the fuel door is the are statements to use 91 or higher octane fuel. The cylinder head chamber from the 97-99 25D heads has a clover leaf quench design. The piston relief design is a single square dish. It's all about how the air enters the combustion chamber and how it's compressed and burned. The shape and the flow of air upon entry has quite a bit of effect on how the fuel/air mixture is burned. It is safe to use 87 octane in your 98's motor because the design doesn't cause pre-detonation with fuel of that octane. The owners manual recommends 87 octane (or regular) for 97-99 25D models. The cylinder head chamber on the 96 head is the same as any cylinder head that is on any other EJ Subaru turbo motor. There's no quench. The piston has 4 separate valve reliefs on the piston surface in the shape of a half moon. Pre-detonation of the fuel occurs when anything less than 91 octane enters the combustion chamber. Link to comment Share on other sites More sharing options...
DOHCEJ22E1 Posted June 6, 2013 Share Posted June 6, 2013 Kenny is correct in everything that he has said. On the brighter side of having a 96 25D, one could use an ECU for a 97-99 25D & it should allow the engine to safely use 87 octane but I have not been able to physically sample a 96 GT yet (like tear one apart), so I don't know if the ECU is able to just be plugged in. Only 97-99 GTs & Ls. The 97-99 ECUs are more open to physical & burn characteristics from the engine & will adapt the engine as best as it can to the parameters it has. For example, I have 97-99 25D heads on a 95 22E block & my ECU (a 98 25D ECU) has adapted to the block by sensing changes in the intake vacuum & exhaust heat. Being that the 96 25D burns gasoline differently than the 97-99 25D, the physical compression is still 9.5:1, which means that the ignition & gas entry to the chambers will be adjusted by the ECU to operate within a "comfort zone", so to speak. It can be done but you will have to try it. As long as you are using your car's ECU though, you must use 91 octane or the engine will knock. Link to comment Share on other sites More sharing options...
Kennyfvholla Posted June 6, 2013 Share Posted June 6, 2013 The 96 ECU can be unplugged like the 97-99 ECU's. I'm not sure about being able to use regular fuel with the 97-99 ECU, but I wouldn't know for sure. Yes, the later ECU is a bit more flexible in how it adapts and compensates for input to tolerances. But, I am still not sure that it can adjust timing far enough to compensate for the pre-detonation caused by the physical differences. Even if it could, at that point, timing would still be altered so much that the decrease in power AND the decrease in fuel mileage is just not worth the few penny's difference in cost of fuel or messing with swapping ECU's. Link to comment Share on other sites More sharing options...
Frougy Posted June 7, 2013 Author Share Posted June 7, 2013 I've been hearing from all sorts of people saying that I can use regular gas instead of premium gas. My gas mileage is bad because the AT TEMP OIL light flashes 16 times at start up along with the torque bind. So im averaging 20-21 instead of 22-25 Gas by me in Illinois is $4.40 for regular Link to comment Share on other sites More sharing options...
Zues Marine Posted June 7, 2013 Share Posted June 7, 2013 F that man, its 3.80 up here for the cheapest.. i hear 'gas is supposed to go down soon' but that sounds like the media's usual go-to line when they hike up noticeably quick Link to comment Share on other sites More sharing options...
Kennyfvholla Posted June 7, 2013 Share Posted June 7, 2013 No. That's not why your gas mileage is bad... I had the same torque bind issues on my 96 LGT. I could easily get 23/24 mpg around town driving the car like a normal human being. You'll never average more than that, even after it's fixed. Torque bind occurs only because the car isn't able to compensate for the wheel speed differences at low speeds. But really though, do what you want. If you want to run your motor on piss to save $10 to $15 a month go ahead. Yes, it adds up. But, at least to me, that little in the long term won't matter at all. I'm out. Link to comment Share on other sites More sharing options...
twisty Posted June 7, 2013 Share Posted June 7, 2013 i said this in the other thread we talked about this also. my 96GT started pinging with 87 octane so i switched to premium and it went away. my 95 ej22 wagon runs 87 all day and never has an issue. thats why i didnt think of using premium in the new one when i got it. Link to comment Share on other sites More sharing options...
Thomistopheles Posted June 7, 2013 Share Posted June 7, 2013 F that man, its 3.80 up here for the cheapest$3.95 for 87 here. $4.09 for 89, and I think $4.25 for 91. Link to comment Share on other sites More sharing options...
Zues Marine Posted June 7, 2013 Share Posted June 7, 2013 guess i should stop bitchin... Link to comment Share on other sites More sharing options...
Zues Marine Posted June 7, 2013 Share Posted June 7, 2013 nah, $~4/gallon is cray Link to comment Share on other sites More sharing options...
DOHCEJ22E1 Posted June 7, 2013 Share Posted June 7, 2013 The 96 ECU can be unplugged like the 97-99 ECU's. I'm not sure about being able to use regular fuel with the 97-99 ECU, but I wouldn't know for sure. Yes, the later ECU is a bit more flexible in how it adapts and compensates for input to tolerances. But, I am still not sure that it can adjust timing far enough to compensate for the pre-detonation caused by the physical differences. Even if it could, at that point, timing would still be altered so much that the decrease in power AND the decrease in fuel mileage is just not worth the few penny's difference in cost of fuel or messing with swapping ECU's. There are people using 97-99 ECUs w/96 25Ds & have not reported any pinging but on the same note, those same people haven't reported much of anything after stating that they are using the combo of the 2. I believe that the 97-99 25D ECU has a pretty wide adjustment range & I would recommend nothing less to use in a hybrid engine. I say this because I have used 97-99 25D ECU in 3 different EJ engine types: 97 22E stock (9.7:1 CR). 99 222 w/97-99 25D heads (10:1 CR). 95 22E w/97-99 25D heads (9.5:1 CR current). The ECU was able to run them all very smoothly on 87 octane although higher octane levels would obviously cause them to run better. No pinging from any of these engines & they all got some pretty decent MPGs (all over 30 highway). Now each of these engines obviously burns gasoline quite differently from one another but changes to ignition, intake, & exhaust will also affect the way an engine burns gasoline to a limited extent. This ECU is far more capable than the EJ22E ECU, which itself is a pretty capable unit despite it's lower rpm limits. I'm speaking from experience with it. It's exceptionally good with hybrid builds unless the physics of the combustion chamber far exceeds it's adjustment capabilities (like CRs that range into the 11s). This leads me to believe that the 97-99 25D ECU is capable of controlling the 96 25D safely. Link to comment Share on other sites More sharing options...
PorkchopSandwiches Posted June 7, 2013 Share Posted June 7, 2013 nah, $~4/gallon is cray Shoot, man... I'm on the west side for the summer and I miss Spokane gas prices so bad. At the start of summer just about everything here was 4+. Makes it even worse that I commute for an hour every day now. Link to comment Share on other sites More sharing options...
Kennyfvholla Posted June 7, 2013 Share Posted June 7, 2013 DOHC, I'm agreeing with everything you're saying, I still think that even if the ECU runs the motor well on 87 octane that it could impead power and fuel mileage too much to be worth it. That's all. Link to comment Share on other sites More sharing options...
spooln30 Posted June 9, 2013 Share Posted June 9, 2013 I read that for the second gens only the 96 2.5 needs premium gas and the 97-99 2.5's don't. I run 87 in my 99 LGT w/o any issues. I wonder what they changed in the later years. Maybe just the tune would be my guess. Link to comment Share on other sites More sharing options...
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