T O P

91 Octane Gas isn't available. Can I mix 89 and 93?

91 Octane Gas isn't available. Can I mix 89 and 93?

707amt

Why not just use 93?


KiteLighter

That's not my question. As you see, I have been using 93. My question is: "Is there a reason not to use 91 mixed myself?" or "Is there a difference, in this car, between 91 and 93?" or "Is there a downside to using 91 instead of 93?" Care to help?


Dodoz44

Price difference. It adds up in the long run.


707amt

If you have to worry about a few bucks when filling up then you have other things to worry about.


TubaCharles99

O I bought this expensive car how luxurious. A month or two later whines about how they can't afford the things with it. Sounds like people need to do their damn research on the car they buy before buying it.


Unspec7

You also tend to stomp on the gas more when running lower octane to try to match the response you're used to seeing on higher octane gas, negating much of the cost savings. Edit: lmao what up with the downvotes, engines pull timing when you use lower than recommend octane


Slimy_Shart_Socket

I did the math for a co-worker, he was averaging 7-15% less per tank. But our 87 Octane contains up to 10% ethonal.


Unspec7

Less per tank as in less mileage?


Dodoz44

Be my guest, waste away.


mrcompositorman

Why the fuck would you own a 700 horsepower Corvette if you’re worried about being “wasteful” with fuel economy lol


Dodoz44

I'm not OP, and nobody was talking about fuel economy, where'd you even pull that one from? There's no reason to run higher octane than recommended except for throwing money away.


clutchthepearls

If you really need to save $4, probably just walk instead.


KiteLighter

That's not my question. As you see, I have been using 93. My question is: "Is there a reason not to use 91 mixed myself?" or "Is there a difference, in this car, between 91 and 93?" or "Is there a downside to using 91 instead of 93?" Care to help?


jdrch

> recommended gas is 91 octane 91 is a *minimum* value, so 93 will be just fine. You're actually pretty lucky that 93 is widely available where you are. Here in the deep upper Midwest you're lucky to find anything over 91.


Clienterror

Northern Illinois we have everything depending on the gas station. I’ve seen 87,89,91,93,98,and E85 within about a 10 minute drive from my house.


jdrch

> 98 WOW.


KiteLighter

Interesting. What does 93 get you that 91 doesn't? A cleaner engine, more MPG, more HP? Thanks for the help.


Foman13

Higher octane ratings resist pre-ignition. If you are not experiencing pre-ignition (pinging), a higher octane rating does nothing.


jdrch

> If you are not experiencing pre-ignition (pinging) Modern cars pretty much *never* experience this because the ECU detects and mitigates knock in real time,^1 typically by derating (read: running at lower power) the engine.^2 The higher the octane rating, the better the ignition/combustion process is and the more power the engine (theoretically) can safely (without knock) produce, and so the better performance will be. ^1 I forget whether this is done by a fuel sensor and then the engine lowers its power to prevent knock at all the engine detects knock 1st and then lowers power output until the knock goes away ^2 This can also result in the engine running in non-design conditions, which may damage it


TheThunderbird

Yes, you could do that. The pump does this when dispensing 91. IMO, you should just pump 93. Generally, 93 is recommended for most German luxury cars anyway, but since you can only get 91 in some places they go with that as the minimum recommendation.


A_1337_Canadian

Most of Canada just gets 91 max. Really hard to find 93 or 94.


fuckyoudigg

Only a few places have higher. The Petro Canada's that were Sunoco have 94 and some smaller independent networks have 93 or 94.


hkan333

100% of Chevrons have 94 here in BC


Glarmj

The octane measurements in Canada are different from the US, Canadian 91 is about the same as American 93.


A_1337_Canadian

We all use AKI. The differences might be in the naming (regular vs midgrade vs premium) but a 91 octane fuel is still a 91 octane fuel.


Slimy_Shart_Socket

The local tuners in my area have actually proved our Chevron 94 or Shell 91 is worse than US 92 Octane.


Clienterror

No way!? We need to blow the whistle on this ASAP.


clutchthepearls

That's Europe, not Canada, and our 93 is their 98 in that instance.


christobevii3

Octane has an elevation value in it...your 91 would probably be 93 in florida.


A_1337_Canadian

No. Altitude changes the octane *required* for performance but it does not change the rating of the fuel. Test your 91 octane everywhere and it has the same AKI. That's why you see 85 as regular in Colorado. It's to counteract the altitude. It's still 85 AKI in Florida.


KiteLighter

Thanks! What does 93 get you that 91 doesn't? A cleaner engine, more MPG, more HP? Thanks for the help.


phulton

I don’t understand the purpose of doing this. Higher than recommended octane has no negative effects on the vehicle. Just don’t go under what the manual says and you’ll be fine.


people40

I believe the purpose is that 89 is cheaper than 93.


phulton

I don’t think someone should own a 15 year old bmw and worry about $10 per fuel stop, but hey that’s just me.


people40

There's no sense in lighting $10 on fire for no reason at every fuel stop no matter how much money you have. Higher octane won't hurt anything, but it generally won't help anything either.


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phucyu138

> Most ECUs will run the engine rich on lower octane and it'll just cost you more in the long run. No they don't. The ECU cuts ignition timing when lower octane is used.


Unspec7

I was gonna say. Why would more fuel prevent knocking lol


phucyu138

More fuel will prevent knocking because the unburned gas will act as a cooling agent inside the cylinder to cool it down but that's not how modern ECUs work because they cut timing instead to achieve the same thing but at the cost of power.


Unspec7

Pulling timing seems much more reliable as well


people40

If you use lower octane than recommended, this is true and you will get worse performance and fuel economy as a result. However, the converse is not generally true for higher than recommended octane, which is the context of the post. If you put 93 in an engine designed for 91, you will not see better performance or fuel economy.


TheR1ckster

True u think I misunderstood the context. Around here in Ohio we really don't have many places with 91. Its all 87 89 and 93.


KiteLighter

DINGDING! There's the answer I've been waiting for: "but it generally won't help anything either." If there's no benefit to 93, then I might as well save my money if it doesn't inconvenience me.


KiteLighter

I don't worry. That was contained in the question. I wont be inconveniencing myself by doing this occassionally. But if I can save $10 per stop without inconvenience or losing some benefit 93 provides, why wouldn't I do that?


John_Sux

But it's North America, gas is mostly cheap.


BassDrive

Just use 93, don't mix.


instaweed

93 is fine. Some states don’t even have 93 and the cars that run 93 from the factory perform just fine on 91.


scr3wballl

Need to realize there is different octane for different regions. Higher elevations use lower octane to compensate for less oxygen, which is the rating used since that covers larger portion of the US. 91 octane at higher elevations is equivalent to 93 at lower elevations. Then it doesn't help with ethanol free, E15, and E85 having their own ratings as well but can cause the ECM to have to adjust more drastically than usual.


Old_Goat_Ninja

Yes that’s how it works. Kind of pointless to do that though, 93 won’t hurt.


Fair_Still6667

Yes, its fine


LR_111

Just use 93


PassionFlorence

Big brain right here. Why are you trying to mix? Just use 93.


KiteLighter

Why not. If my car is going to be sitting at the gas station while I buy something, it's worth 30s of my time to get a full tank and save a few bucks. Does 93 get you anything 91 doesn't, in an engine tuned for 91?


PassionFlorence

Just get a full tank of 93. Why mix when you should just get 93 if it's available.


KiteLighter

Not the question I asked. What does 93 get you that 91 doesn't, in an engine tuned for 91? Can you help me out, here? "Buy 93 because expensive is good," or "Buy 93 because black magick" isn't an answer I'm interested in. I want to understand the difference in an engine tuned for 91. And don't get me wrong - there's a place for black magick. I work on servers, and there's things I've learned to do for black magick reasons. But I have non-magic theories to attempt to explain those.


TubaCharles99

Use 93 also never leave your car fueling with out you there. That is a dumb ass thing to do and pretty sure is illegal.


KiteLighter

Oh, really? I've fueled cars more than a thousand times, and there's never been any reason for me to be there the entire time. Why is it dumb? Legit question. I've taken to leaving my car fueling while going into the store. Pipelining, baby!


TubaCharles99

Idk you're just never supposed to leave your car unintended while fueling.


KiteLighter

Why not? People do it all the time. Do you live in a super high crime area or something? I don't leave anything in the car that could be easily stolen.


TheOzarkWizard

Use the website find93. Running 93 will probably give you more power as well


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clutchthepearls

That's not how those work, just FYI. Their advertised "raises octane 4 points!" doesn't mean 87 becomes 91, it means 87 becomes 87.4. The octane boosters that actually raise a tank of gas 30-40 points cost about $25 a can.


01WS6

Why would you just not use 91 or 93? You need a lot of those octane boosters to make a difference...


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01WS6

Make sure to read the fine print. Normally they treat x gallons of gas by 0.1(or whatever point they claim), not a full octane point. So its 87.1, not 88. Theres no way you get 87 to 93 by one bottle, not even close.


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01WS6

One bottle aint doing it. Your ecu is pulling timing to compensate for the lower octane.


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01WS6

I assure you that your ecu is pulling timing to compensate for the lower octane. You wont feel it as much unless you are doing full throttle pulls, and if you are doing full throttle pulls then you should be running recommend octane. The higher the octane the less timing will be pulled.


Manafont-

Your ecu is compensating here. Don’t be cheap and just buy the correct gas.


LR_111

Not a good idea.


707amt

Over time the octane boosters will leave deposits on the spark plugs and exhaust of you car. You’re better off just getting the right gas.


Knight1453

We don't even have 93 back home so just use 93. Ours start from 95


Realpotato76

AKI vs RON, différent systems of measuring octane


01WS6

>Ours start from 95 Your octane rating is different from the US then


NoUnderstanding7474

They should just delete this post, all the downvotes lmao