Hey guys, I was doing a little searching into what fuel grade I should use in my WRX, 87 or 91. I couldn't find anything on this forum, but I came across this thread that explained the differences really well and thought I would share...
Kind of interesting. Even though there's no additional energy in 93, I suppose it makes sense there is a potential mileage boost from running more efficiently, assuming your car knows how to take advantage of it.
I have a bone stock 04 WRX. Just picked it up, don't know what the previous owner was running, didn't cross my mind to ask... All I can find around me is 91, which I don't think there is much of a difference from 93.
Do not EVER run anything less that what is recommended, 91 octane. If you want to run regular, you need to buy a different car, or perhaps get it tuned for regular? (idk if this can even be done, nuke?)
I have a good healthy fear of the knock monster. I'd say don't buy a turbo if you're concerned with mileage in the first place... It does give me a little more justification with the Mrs. though. Always a plus. Fienix: Do you have an BP's near you? They all have 93 (as far as I'm aware). All SA's should have 92.
I was going to say... stop shopping at Holiday and you will find 93. Any BP in the metro area should carry 93. I am pretty sure you can also find 93 at most Shells.
I'm sure a car can be tuned for 87, but is it worth saving $4 per fill up vs paying someone for a tune? lower timing and boost and add lots of fuel...doesn't seem to be a good thing. should've gotten a RS/2.5i
it can be tuned for 87 but its pointless like everyone has said. you will lose alll your power even compared to the stock feeling and wont gain much as gas milage will drop off as well. stick to 91 and suck it up or sell the car and by a prius
Funny, I have yet to find one in the cities that doesn't have 93. However, when i was on 93 I was stopping @ BP most of the time because there isn't a lot of Shells by my house. The Shell by my house is on Dale and across the street from a BP so I only stopped there once. either way... where are you shopping? I really haven't seen a Shell with 92... I even stopped @ one in Southern Minnesota on my STL roadtrip the other week, and they had 93.
Edina, Prior Lake, I think a couple others. So now I only pump at BP. I was very surprised they didn't have 93, kind of annoyed actually lol.
Looks like i need to snap some cell phone pics for you boys. It does exist, the only time i have run into less than 93 @ Shell was in Iowa. Even the Shells I stopped at in MO had 93.
I have a almost completely stock 04 WRX, and my general rule has been 91+. The holiday by me, (Hamline/Marshall) has 93. But I have not noticed much difference in fuel economy or power from 91 to 93.
Wasn't complaining. I'll pump premium all day if that's what's best... Just thought the link had some good viewpoints on the different grades/prices.
I'd like to see how much the car knocked on 87. That would be a bigger concern to me than saving a couple bucks at the pump.
Once, in my old sti, I accidentally filled up with 87. Had about 1/8th tank left of 92 but once I got into the fuel that was straight 87, yikes. Painful sounds I still have nightmares about. Ended up dumping in a can of Toulol i picked up from Menards.
Ohhhh, bummer. Good to know. Thankfully I haven't come across one that didn't have 93 yet in my travels all over the metro. AP is always on standby just in case though...
the funny thing is, i just had a convo about this on monday with a guy about this. He told me that there is no car on earth that needs premium. He says people are stupid and wastin money when they fill up. So i asked him bout cars knocking wit lower octane, and all he said was cars run more efficient with higher octane nothing is wrong wit a little knock. His wife has a merc c-class kompressor and he tells her to put nothing else but reg 87-89 octane in her car, since its a waste of gas/money. And after i questioned him more bout his opinion, all he had to say is i know what i am talking bout cuz i have a masters in mechanical eng. and told me to stop putting premium in my car. that was a snippit of a 20 min convo. Do you guys agree with what he is saying or no? sorry if it not make sense, as i am writing this at work.
In my experience people that can only respond with "I know what I'm talking about..." but can't actually support their reasoning, don't really know what they are talking about. lol. Different octane gasoline will have different combusting points under compression the way I understand it. So you must be tuned for it I would think.
I have noticed that if the car states "premium fuel recommended" you do not need to use anything other then 87 octane. you just get better performance and fuel economy using the premium fuels. If your car states "premium fuel only" You have to use at least 91 octane. Not all forced induction cars need premium the new Nissan Juke does not. My mercedes did not but they were recommended for the best performance.
Your co-worker with the masters in engineering is an idiot. I know what I'm talking about, I've worked with retards before.
Tell your co-worker that you will GIVE him a 2011 STi if he agrees to ONLY pump 87 octane gas in it. And that if it blows up, he has to buy the car outright. Also, I get to pull his pants down and laugh at his genitals...in public
They had 92 as their premium fuel for quite a while, but switched back to 93. The switch took a while and during it either 92 or 93 could be had depending on where you went. I'm pretty sure 93 is the standard across the board in this area now. 91 is common up north and in Wisconsin though. Those of you on stock tunes probably don't need to worry about finding anything better than 91. That is the minimum standard for premium across the nation and most cars that state "premium required" or "premium recommended" are referring to 91. There may be some learning ability to take advantage of higher octane with boost and timing, but it's not likely to be very noticeable. Less than 91 is just a bad idea.
Thats what i was thinking. Even what he said was true, i asked what was the point buying a car like that if you are only going to run the lowest octane in it. Why would anyone buy a car to make it run less efficient. Now i not an expert, but if you drove it "conservative" it would be ok wit the lower 87. But once you start to boost thats where the problems start then, correct? He also said you would get more carbon build up wit the lower octane and have to rebuild the engine sooner....ya b/c that will totally offset saving a dollar or two every fill up with the lower octane. After awhile i could see i was getting no where in this convo.
I've seen BP's locally with 91 in the past year (there's one on Hennepin in Uptown, and I think another in Plymouth/Maple Grove off 169). But you're right, 91 is just fine to run. I'm nearly stock, but have a stage 1 tune, and have had no issues filling up with 91 if 93 isn't available. Some of those smarter than me can chime in, but I'm pretty sure this is correct. Stay out of boost if you absolutely cannot find 91 or higher out in the middle of nowhere.
Yeah, drive it like an old grandmother. Stay out of boost entirely. Never go wide open with it on 87.
I am not sure what the stock tune was on the earlier cars... but I know my 09 said pump 93 only in the owners manual. It seems like the earlier cars were tuned to 91 on the stock tune from what people are posting?
In my 2.5i I've used both and with regular there just doesn't seem to be as much get up and go as there is with premium, it really shouldent matter that much because its not like the computer knows that kind of gas is being put in the tank, the engine still works the same way, fuel is injected and ignited by the spark plugs...But the car does seem to pull harder with premium in the tank, unless 91 is really that much more explosive then 87...I don't know I'm not a petroleum engineer, just a mechanical one
From what i took away from my fuel systems class when i was attending college(oooohh), we had covered the fuel types. Premium has a higher tendency to burn smoother and the expanding gases are more consistent and uniform during combustion therefore better performance, rather than the explosiveness of regular and the combustion is more erratic or irregular through preignition, detonation or multiple ignition sources (none are good, hence knocking/pinging when used). At least that is how i have come to understand the purpose of having different fuel grades.
Octane is resistance to ignition. This resistance to ignition is also a resistance to pre-detonation. You need 3 things to make fire. Ignition Source/Heat Oxygen Fuel A naturally aspirated car receives a volume of oxygen equal to the volume of the cylinder at atmospheric pressure. This oxygen is mixed with the misted fuel then ignited by the spark plug. Now, let's put a turbo on there. We are now forcing more oxygen into the mixture making the mixture more volatile. If timing and fuel stay the same, this is going to likely pre-detonate. By increasing the temperature at which the fuel ignites, we can slow the point of detonation of the mixture. On top of this, you can change the timing of that spark to allow more of that air to enter the cylinder before it ignites. This is the very basis of why you need to run the higher octane fuel in a turbo car. They have been tuned so that the ignition time for the spark plug is set to go off at a point when X amount of oxygen has entered the combustion chamber with Y amount of Z octane fuel. If you put in an octane that is <Z, the engine will knock, because the fuel will ignite before it was intended to....pre-detonation. And pre-detonation is BAD.
Premium doesn't have a higher tendency to burn smoother it just has a higher resistance to burning and pre det.. The cylinder/head and spark plug determine the burn quality. But I cant believe there is a month long post on this if anyone tell you 87 is fine for a turbo/super charged car flat out slap them(unless they drive an old Volvo stainless steel. I think those could literately run on and fuel type but diesel.) What readymix is saying is 100% on point. Just an FYI Shell gas is junk we did tests on it in college and found the one near our school was about 85 oct not even close to 91 it claimed. BP had the best gas their octane was spot on to the label. On a side note putting 91+ in a car that doesn't need it will harm it over time and slowly choke it with carbon build up. Since the car isnt designed to deliver enough spake to burn 91+ some leftover dont get pushed out during the exhaust stroke and stay behind to cake your head an pistons.
And this will also hold true to a wrx/sti. If you put 93 in it and just "cruise", your low compression motor will not like life. This is where the street tuning pays off. your 8:1 motor doesn't need 93. Hell, it probably doesn't need 87, but as soon as you get into boost and the cylinder pressures start to rise, you will need the octane. I am running almost 3-4 degrees more timing while at cruise than the stock map. I am also getting 3-4mpg better mileage while cruising. I am able to maximize (or atleast better utilize) the higher octane while off boost. Russ
Mainly, I figure the difference in pump price from 87/89 and the 91+ isn't great enough to even bother concerning yourself with pinging/detonating or always having to stay out of boost. You're not saving enough to be worth the hassle. These cars are too damned fun to drive to baby 'em all the time.
