The signs I see for this always say collector cars or small gas engines. There are a couple gas stations up north (Garrison area) that only offer this in 91 octane. Is this safe to use in the car? Is it preferred? I haven't had much experience here with it in the cities.
It's fine to run your car, in fact you'll probably get better milage. Non-oxy means that there isn't any ethanol mixed in, meaning the fuel won't go bad as fast as the mixed fuel. That's why they market it for small engines or classic cars because fuel might sit in those tanks for a while without running or adding more fuel.
It's very bad in our turbo charged cars. It's basically worse then 87 octane and if your boosting around with it you are going to get tons of feedback knock, especially if your car is tuned.
Additionally, the ethanol deteriorates rubber found in older style fuel lines and carb float seals. When it breaks the rubber down, it clogs narrow passages in the carb and you end up cleaning it more often if it doesn't lean the engine out. Classic and small engines don't have o2 sensors which would otherwise protect lean outs like that.
I run it in my supercharged BRZ. No issues, better mileage and a better feel than 91. I also use it in my liter bike as well as yard equipment. I see no problems with using it at all. If your tuned always ask the tuner if you're concerned.
My understanding is the same as Jesse that you should not run it due to the fact there is no ethanol in it. The ethanol levels even in 93 are what help you run higher timings along with the higher octane rating. Without having ethanol then you are unable to run as cool of engine temps and run a higher risk of having issues with knock and detonation. Looking forward to some in formed information on why this is ok to run in a vehicle running a safe 93 tune.
Ethanol is way more resistant to knock or detonation. If your car is completely stock you may be able to run it (still not the best thing for it). But if your car is tuned, even on 91 with 10% ethanol which is normal 91, you will get knock. Talk to any tuner and they will tell you that 91 non oxy is not good for our cars and that these cars like the ethanol. That is what allows you to get more aggressive with your tune and allows you to make more power. Same as getting a 93 octane tune vs a 91 octane tune, your car is going to be faster with the better fuel if properly tuned with them.
I have talked to my tuner and it was said that, on my 91 tune, I can use 91 to 93 and non oxy with no issues.
And that is fine if that is how the car is tuned and setup to run. Hell you can tune our cars to run on 87 if you wanted to. It would run like dog **** and have no power but you can do it. Jesse is going off the information provided by the OP and he took the correct stance (IMO) 91 non-oxy is not a good gas to run in our cars. Now if Russ comes back with some information that supports his opinion great id love to read it but every tuner I have talked to and the small bit of my own tuning I did on my WRX lead me to the same conclusion. Take away the small amount of ethanol that comes in all our gases now days and it increases your chances of knock/detonation substantially.
Info like this is good, there are some benefits to running 91 non oxy like this and other stuff too. But there is a reason there is a warning label on it at the pumps explaining when and what to use it on. Your car can be tuned to run on whatever fuel you choose, but this fuel is way prone to detonation in our cars and you have to dial back the timing a ton to keep it from knocking, making it so you make way less power then regular 91 with ethanol.
To explain the logic behind ethanol knock prevention... Ethanol requires more liquid volume per ignition compared to gas to output the same amount of power. For a subaru, the ecu adjusts fuel trims based on the O2 results until the O2 sensor reports 1 Lamda, which is different depending on the amount of ethanol. More ethanol requires more volume of liquid to reach Lamda. The knock prevention comes from the extra volume of liquids ability to absorb more heat as it enters the cylinder. The cooler the cylinder air is during the compression stage, the less of a chance the fuel will ignite prematurely from compression. Additionally, Ethanol requires more heat to ignite (higher flash point). The reason it's arguably bad for turbo cars to run non-oxy is dude to 3 things, heat/boost and timing. Heat/boost: The higher volume of air will result in a higher compression at top dead center. If you know how diesel engines work, you'll know increasing compression will result in ignition without spark. If the cylinder temp and pressure is higher, the fuel is more prone to early ignition from the higher volume of air, espcially when there is less fuel to absorb more heat. Additionally, heat is generated from a turbo when air is compressed, as you are smashing air molecules closer together at a higher rate, hence why we have intercooler. You can run fuel richer to accomplish the same effect ethanol has, but being over rich impacts performance. The amount of fuel also affects timing properties.. Timing: In general, if a tune has too much advance timing, the cylinder pressure can peak before the piston is at an ideal angle (max power crank angle) during the power stroke (15 deg. after top dead center (ATDC) I believe). Tuners typically push boosted cars to the point of knocking and pull back a few degrees of timing to get a safe timing map, and without going into to mcuh detail, boosted cars will knock before they will reach max power which is why this is done. Knock being a noise that the ECU hears when peak cylinder pressure spikes before max power crank angle. If the timing is set just under that knock threshold for a fuel like 91 with 10% ethanol, running 91 non-oxy could pre-ignite easier (refer to the information I mentioned above) and thus generate more pre-ignition events. With all that said, a tuner can accommodate for some of this. Every car runs a little different and every tuner has their own adjustments they make. Some may pull more timing after reaching knock or MBT (Lowest amount of timing needed to reach best torque without knock), others add more fuel or less boost. Weather also impacts ignition properties which we don't notice as the ECU is trying to adjust fueling on the fly. I feel like I glossed over a lot but I think I hit my points. Edit: Because I'm not busy at work and got on my soap box, I'll keep going. The infamous "ring land failure" is likely due to advance timing and lean fueling conditions that lead to higher cylinder temps. Thinner metals heat faster than thicker metals, so the compression rings around the piston notoriously expand faster than the diameter of the cylinder. When you have an engine at operating temp, and drive it like you stole it, the cylinder temps will skyrocket and the rings are the first thing to expand. That's why ring gap is important in engine building. too much gap creates blow by. Too little will cause the gap to close and the ring expansion will damage the piston. Usually by pushing the rings (like earths tectonic plates) into the ring land (the void in piston that holds the rings). There are other factors that impact engine temps but that generally covers why rings fail. It isn't just Subaru that have this problem, but they seem to be engineered in such a way that they are more prone. maybe the ring lands are too close together or the fact that the apposed cylinders may wear unevenly? I guess I don't understand the engineering enough to say for sure.
Man your woman must love when you talk dirty to her because all this good information got me like mmm baby.
*thumbs up! that's all I have to say. Can't really argue with that explanation, if you can I am very interested. Because that's the very in depth explanation of what I know about it.
She frequently asks what I am working on so I just start explaining. She typically responds with "I don't understand but don't stop". Oh yeah?.. challenge accepted. I forgot to mention that ethanol is hygroscopic (absorbs water) and petro (gas) is hydrophobic which means: or in other words, ethanol based fuels tend to separate over time due to moisture in the tank. Worse because Minnesota summers are so humid. If you use it within its shelf life, you shouldn't have a problem. Weight wise, water is heaver than Ethanol which is heavier than Gas. You end up with moisture absorbed ethanol entering the engine first before the petro gas. The 10% in pump gas is usually fine unless you park it for longer than a month or so. I noticed this first hand when I let my STI sit for a little longer than a week and my ethanol sensor spiked on first start to 84% and then back down to 81% after driving around a while. The car felt like it ran fine but I could tell there was bad fuel, as the Air Fuel Correction/Learn ratios swung wildly on my access port. I never had that problem on 10% 93. I have also pulled the carburetor off of my old mustang and seen green "gunk" and "hazy fuel". My best understanding is that the green gunk is oxidized brass (because of water) of the floats, and the hazy fuel was the dissolved rubber from lines and seats. That "gunk" clumps together into a film like yuckiness because of some science reasons. that film can clog passages and can lean out engines that are unable to protect themselves (see above). TL;DR of this thread: 10% ethanol is fine if you use it before it separates. Ethanol is "good" for boosted cars as they can help prevent pre-ignition, especially cars that are aggressively tuned. Non-oxy could yield better gas mileage but a economic tuning strategy is needed to see big gains, however, similar results can be obtained from ethanol too. (I didn't get into this but could if anyone is interested)
Maybe I am missing something, but I don't see any reference to a tune in the OP. While I will not argue that having a tune on one gas, and changing to another can cause issues; I do not agree that generically running 91 non-oxy in a WRX is a bad thing. This advice is misleading...
To respond to OP as suggested: Non-oxy is fine to run in cars that aren't aggressively tuned. Some engines handle knock better than others. There are more advantages to running ethanol fuels on boosted cars than non-oxy unless the car sits for long periods of time. Subaru recommends at least 91 octane (93 for sti). Octane is the measurement of knock prevention and behave similarly with or without ethanol. Low levels of ethanol (10%) "convinces" the Subaru ECU into adding more liquid per combustion to lower cylinder temp. Its like... tuning with choice of gas, without changing your tune. Edit: not from a performance aspect, but from a reliability and knock prevention aspect.
One thing I think everyone is forgetting is that the non-oxy gas pumps in Minnesota carry this signage:
Ehh. Signs exist so people can follow directions without needing to fully understand something. They also exist for people who lack common sense. I have a lot of theories behind why this sign exists, but nothing creditable. I lack the experience to say for certain, but non oxy 91 isn't worse than 87 with 10%. The ethanol is really only a bandaid, or a ecu slight of hand trick. It's impact on knock prevention is debatable, but I doubt it'd significant enough to compensate for 4 octane points. I need to switch back to pump gas soon so maybe I'll try different octane and ethanol amounts and post the results.
Good stuff guys, I was told by a dealer last year that 91 non-oxy is ok to put in the '15 WRX, no tune.
My point was that Minnesota law requires a minimum percentage of biofuel content for motor vehicles with certain exceptions allowed. Although maybe Subarus qualify as "small engine". https://www.revisor.mn.gov/statutes/?id=239.791
I do not have a tune. Only axel back exhaust. It is something I always wonder about. I hate all gas that isn't 93 octane for my car, lol. So I refuse to stop anywhere most of the time and only get like 3-4 gallons to get me home. I have never actually used the 91 non oxy in my car. I kind of disagree with this logic a bit though. In South Dakota where I went to school their mid grade was 10% ethanol (89 octane) their premium was 91, and their 87 was NO ethanol. I always thought it was weird because 87 cost more than the 89 so I always got the 89 (I had a non turbo Eclipse at the time) If you assigned an octane rating to Ethanol isn't it much higher? like 98? I could be mistaken. That is why I asked. I wouldn't want to harm my engine by making a stupid mistake. Also, my car does not sit for more than a couple days as it is my DD.
So Mnelson hit most of the important points. My biggest issue is the fear mongering the running non-oxy will instantly kill the motor. Not going to happen. At the end of the day, these are all low compression motors, and everything goes back to cylinder pressures. If you could tune to cylinder pressure, you would have the most impressive tune ever. So a couple of break out points. Timing is a crutch for poor airflow. You take the old 02 wrx with the tiny td04 turbos and you were running 30-36 degrees of timing through the meat of the power band and some cars would pull 37-38 up top. Throw on a big turbo, those numbers drop like a rock. I think I was barely into the 24-26 degrees of timing with my 18g setup. The big turbo will cram more air into the cylinder and the timing is just making the spark happen a bit before TDC. So once the piston sweeps over TDC, you want your max cylinder pressure to push the piston down with as much force as possible. Now, you get into the newer 08+ motors and your timing maps are completely different. Those motors flow air sooooo much better that the older ones, so once you get intot he tiny turbos, your timing is already lower that the old stuff. More airflow, less timing is needed. Port, polish, port match, you need a retune. Coat your pistons and chambers with something like swain tech, you need a retune. Hopefully this will explain the airflow side of things. Fuel vs timing. So we know that with a constant airflow we need spark to happen a few degrees before TDC so the by time the piston sweeps past TDC we are creating max cylinder pressures (based on fuel, airflow, etc). Now, with the non-oxy fuel, it is a quicker burn since the ethanol is not slowing the burn process down, so the timing can be closer to TDC (smaller number). Ethanol based fuels burn slower, so you can start the burn sooner (farther away from TDC, larger number). Now based on what/who's fuel you are running those numbers will start getting very tricky. Just like the guys that run e85 can tell you, no ethanol blend is going to be the same. Most pumps currently are 15% ethanol and I know they are fighting to repeal the Pawlenty deal that is supposed to bump the pumps up to E20 by 2020. Now since the ethanol is blended by volume, your 93 E15 might only be 91 E10 or 95 E20. 91 non-oxy is always 91 octane (assuming you get it from a good source). So for a certain load point on the map, we need a certain amount of fuel and our timing number to get our spark to happen at just the right time to make sure we have max cylinder pressure as the piston sweeps over TDC. You want that flame front to be pushing that piston down. Now with constant air and constant timing, if the fuel mixture changes (more of less ethanol to chance the octane rating), you bang will happen at different times, making the flame front happen at different times. The bang/flame front happens too soon, you have knocking. If it happens to late, the last of the flame front is burning as the piston reaches BDC. Both equally bad. Actually, a late burn is way worse, because your knock sensor won't pick it up and unless you are running a EGT you would never know it even happens until you need to replace your rod bearings. So to summarize this wall of text (and the reason I didn't want to pounds this out at 4am). We tune the motor to maximize cylinder pressure and to make the flame front push the piston down. What kinda of fuel you run will allow you to run different timing to try and accomplish the same task. Since most people don't run a EGT gauge anymore, you will never really know if you are even getting to the max potential cylinder pressure. Now if you tune to the ragged edge on 93 ethanol blend, 91 non-oxy will not make your motor happy at WOT through the meat of the torque band (highest motor loads). You don't have the ethanol to slow that burn down enough to compensate the the advanced timing (or higher airflow). Of course, anything other than 93 will not make your motor happy, even other stations that have old 93 will not make your motor happy. And really, you are talking maybe a 10-15hp difference on the top end with a degree or 2 that you could gain by running 93. And if you tune to the edge on 93, good luck leaving the cities. Most places outside the cities are lucky if they have 91 much less 93. It is funny watching people tote around a 5 gallon jug of race gas so they can mix the 89 out in the middle of BF nowhere to get something close to 93 so they don't knock to death. Well, my thoughts are getting scattered while trying to multitask here, so this is it for now and I will add more later as I think of it. Russ
Can we all agree that BP has the most reliable/stable 93 octane ratings? Or are they not consistent either? I only know of 1 other non BP gas station that has 93, T&T Auto on 66th and Portland in Richfield.
You dove in deeper than I was willing to write out of pure laziness. To add to mess of info, the subaru ecus have dynamic timing advancement that can learn to add or remove timing based on the knock sensor which helps with variations in fuel changes that affect flame front speed.. And fuel trims can adjust based on the burn results due to stuff like environmental changes. While I agree with everything seems to require a tune on a subaru, I feel the ecus resilience is underrated by the community. Older cars with 16 bit ecus have far less flexibility but still hold the same concept. Either way..
Don't be so ugly Tuning/modding only narrows the flexibility in favor of power. The more power you want to make, the more consistent the variables need to be.
FYI: There is also a gas station near Inver Hills College and Simley in Inver Grove that sells non-oxy.
