I’ve heard from some sources that their, their as in other people, car runs better on 93 octane gas when they’re car only requires 87. My question isn’t if that’s actually true or not. My question is this: I’ve heard some, I’m pretty sure this doesn’t apply to everyone, people say that their car, which only requires 87, works better on regular 87 octane than 93 premium octane? Why would this be the case for Some people??
short answer: because the manufacturers designed it that way. The engine computer was optimized for regular fuel
https://www.youtube.com/watch?v=dmNQ66AtyWk
https://www.youtube.com/watch?v=pNGNoIiu-C8
In older cars, usually the carbon is built up and so the compression ratio is higher. So, for those engines if you use higher octane cad, you will get better gas mileage and you feel more power.
Donut Media made a great video on this topic this past Tuesday:
Cheap vs EXPENSIVE Gas: What's the Difference
Check it out...
It depends on the vehicle. Some are designed to take advantage of the higher octane if present to produce more power but not all do. If your car falls into the latter category you're just wasting your money using premium gas. Check the owner's manual.
This is only the case if your ECU cannot advance ignition timing to compensate for 93 octane (almost all modern cars can compensate for different octane ratings with special sensors that detect what octane fuel is in the tank, and almost all cars can adjust ignition timing). 87 octane has a faster flame propagation compared to 93 octane, so it can be ignited really close to top dead center and give you full power. Running 93 octane requires an earlier spark plug ignition to account for the slower flame propagation. So if your ECU cannot advance the timing, it will ignite the 93 octane fuel too late for it to provide a proper power stroke. The piston will already be moving downward by the time it fully ignites, and this causes power loss. The closer the piston is at top dead center when the fuel fully ignites, the more power it makes (more downward force on the piston).
@razmigb
I have never heard of this sensor that detects octane. Do you have a link to one?
Sorry about that...I was thinking of the sensor that detects whether the fuel is gasoline or flex fuel (E85). I mixed it up. But I also stated that almost all cars can adjust ignition timing automatically. This is usually done with the use of knock sensors. If any knock is detected, the ECU will make appropriate adjustments to fix it. Knock may or may not occur if a different octane is used, which is why this varies on a case by case basis. It depends on how the ECU handles ignition timing.
@razmigb
I see.
So non-high-performance engines cannot use high octane fuel because they cannot advance timing?
Well it depends on how your timing gets adjusted. Any engine that's controlled electronically will be able to adjust timing according to octane (or how the fuel is burning as determined by the ECU). It's one of those things where you have to experiment with different octane ratings. If your car recommends 87 octane, you can try 91/93 and see if there is a noticeable benefit. Most of the time there isn't a benefit to using a higher octane than what is recommended (it will just change ignition timing, that's all). You may notice better gas mileage and power
when using higher octane when carbon build-up has occurred in the cylinders (carbon- build-up increases compression in the engine because it takes up space-- Scotty has mentioned this before). However, it is NOT advised that you use a lower octane than what's recommended. This can cause serious pre-ignition issues EVEN IF ignition timing is pulled by the ECU (codes will start to appear). You can add higher octane, but NEVER add anything lower than what's recommended.
@razmigb
Interesting. Do you think that maybe street cars don't benefit from high octane fuel because they aren't designed to build high compression ratios? (rather than it being a timing limitation)
Yeah, usually non-performance oriented street cars don't have very high compression ratios. I'm assuming that's more of a cost thing because you need stronger piston heads and engine blocks to withstand higher compression. Air volume is equally important as well when determining octane. For example, a 2019 Mazda3 has a compression ratio of 13:1 (naturally aspirated) which uses 87 octane minimum, and my 2016 BMW has a compression ratio of 10:1 (turbocharged) which uses 91 minimum. Eventhough my engine has a lower compression ratio than the Mazda, it takes 91 octane because of the forced induction aspect. Forced induction greatly increases the amount of air sent into the engine to the point where "boost" is created (positive pressure in the cylinders). Boosted engines need a higher octane so that the fuel doesn't prematurely ignite from that high pressure in the cylinder. Naturally aspirated engines have a vacuum effect, where it "sucks" in enough air to fill the volume of the cylinder (or even less since naturally aspirated engines are not 100% volumetric efficient), so it can take lower octane fuel like 87 that can handle those lower pressures. In essence, the difference is the "sucking" or "shoving" of air into the engine. Now there are some naturally aspirated engines, like the 6.4 liter V8 hemi, that do take 91/93 octane. I'm not sure why they need higher octane, but I'm assuming because it sucks in a lot of air naturally lol. I hope all this makes some sense though. I didn't want to get too detailed lol.
@razmigb
hmm boost and positive pressure, but lower compression ratio... ok. so more air but ... less air. makes sense
@razmigb
do you think maybe high performance engines use higher octane fuel because it resists pre-ignition detonation, not because it burns at a different speed? Or maybe that burn speed depends on things other than fuel? In fact, is it possible that the definition of octane number MEANS resistance to knocking?
What you're asking makes no sense. First off, octane IS the measurement of a fuel's resistance to ignition under high pressure and heat. And higher octane fuels do have a slower flame propagation because of their resistance to ignition. THIS is why ignition timing is advanced. There's a correlation between octane and flame propagation. I hope you know what burn propagation is by the way. I just stated in my previous comments that high performance engines DO need high octane fuel to resist pre-ignition, and I also stated WHY they need higher octane fuel. You're not reading my explanations clearly. You're trying to play it smart with me again and it's not working. Do you really have no idea on all this stuff?
@razmigb
I'm just listening to your advice, and how you understand things that's all
https://www.sunocoracefuels.com/tech-article/beyond-octane
@razmigb
oh another thing... do you think the engine might be using the oxygen sensor to adapt the ignition timing?
@mountainmanjoe
Yes it does. Depending on how complete or incomplete the combustion was by measuring O2 molecules. If it detects multiple incomplete combustions, it will advance timing to give more time for the combustion to take place (in other words the flame propagation is longer). And the knock sensors are also used too.
Here is a great explanation on fuel octane:
"The problem is that the popular components used to make the octane of a fuel higher slows the burn rate and a fuel with a burn rate that is too slow can result in an engine power loss. Of course, that is just typically what happens and it does not hold true for all fuels. In part 2, we will explore all of the alternative fuels, how they affect your engine’s performance and reliability, and which fuel is right for you."
But guess what...regularly available 91/93 octane fuel at gas stations burn slower because we use ethanol blends as an octane booster (at least here in the US), and ethanol in general burns slower and more completely. But of course this varies by what additives are used as the octane booster. Gasoline is gasoline, it always has the same octane rating until we use additives to increase the octane.
@razmigb
well if the magazine says so then it must be true. The fuel engineers are wrong.
@razmigb
Do you think you might be exaggerating a bit when you say "NEVER add anything lower than what's recommended."
Like what if I'm low on fuel and regular is the only thing available?
It's not recommended, and that's just common sense if you want to run your engine safely without the risk of pre-ignition. You want to listen to the ENGINEERS right? They tell you recommended octane ratings for a reason. Your asking for potential issues if you do this. What you're saying is the equivalent of saying "Oh the gas station only offers flex fuel, so I need to use it since I ran out of gas." And I've never seen a gas station that doesn't offer higher octane than 87 (at least here in the US). One time I used 87 in my BMW to test exactly what you said (because I'm a curious person, I like to experiment around), and it ran terribly with numerous knock codes. I immediately went to autozone and added in two bottles of octane booster to help, and surprisingly it did. Believe whatever you want, I'm not forcing anyone to abide by whatever I mention on this website. If you want to use my valuable information from experience, go ahead. If you don't, then move on and stop with the constant bickering of "What if? What about the engineers? What about this? What about that?". Clearly you're doing research on your own questions before you ask them, so use the information you find. You're not gonna get anywhere in life if you keep bothering people like this...go do something better than playing smart with people.
@razmigb
In fact , I read that if the manual _recommends_ premium fuel (not requires) then you can run regular all the time.
You're gonna believe what a GM engineer says after you criticize their engines and cars on this forum? Ok. And this is NOT the case for all vehicles...if a GM engineer said it then it's definitely GM specific. They cannot speak for other manufacturers like BMW, Toyota, Mazda, etc. It doesn't work that way.
@razmigb
yes we have a voting feature. Please refrain from causing drama. You have been warned.
I find that varying opinions on the same subject are like rectums. Everyone has their own.
@jimz
and most of them stink