The difference between 87 and 91 octane, why it matters for the Si

etcsthorne

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Never in my life have I worried as much as this crowd does about octane.

If you can afford a car you can afford to run good fuel for 6 dollar difference per tank.

If its a lease or you do not care than run the cheapest bargain basement bull that you can find.

If your keeping the car or you care at all about the longevity of the engine, RUN 93-94-95 HELL ID SAY ANYTHING UP TO 100 UNLEADED. Base model OR SI DOES NOT MATTER.

A turbo car is a turbo car is a turbo car.

No matter what safety systems the companies run to allow the cheap jokers to get away with shit fuel; A turbo car WILL GUARANTEED BE SAFER TO OPERATE WITH HIGHER OCTANE.

Did I mention turbo car?

Boost and octane go hand in hand. If we were talking about a lawnmower engine that was turbocharged I'd say the same thing.

If Honda were to tell me directly I was wasting my money I would still waste it using better fuel. From experience.

Forget the recommendations, forget the is 91 ok?, they are all turbo charged small displacement motors under ridiculous load at times for their size.

RUN GOOD FUEL.

I say this spiritedly because I care about the state of health and well being of these cars AND the owners! :)

You need to put a little more emphasis on the needs of engines with turbos. :p Great post, by the way. I agree
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SCOPESYS

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Just to be clear, there is no Gas Octane detector in the CIVIC that will automatically switch the ignition timing ?

The switch of the timing is done manually by the driver, by switching the car between Normal & Sports.

So,
(1) to prevent Pre-Ignition, the driver is responsible to make sure that they do NOT select SPORT mode (ie Sports ignition timing) with Low Octane Fuel ?
(2) If the driver select Normal, and used Premium High Octane fuel, they will get no benefit, and just be paying for more expensive gas, giving them the same MPG as the lower octane fuel. ?
 


saiko21

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Just to be clear, there is no Gas Octane detector in the CIVIC that will automatically switch the ignition timing ?

The switch of the timing is done manually by the driver, by switching the car between Normal & Sports.

So,
(1) to prevent Pre-Ignition, the driver is responsible to make sure that they do NOT select SPORT mode (ie Sports ignition timing) with Low Octane Fuel ?
(2) If the driver select Normal, and used Premium High Octane fuel, they will get no benefit, and just be paying for more expensive gas, giving them the same MPG as the lower octane fuel. ?
Nope, It's not like that. Civic or no other car can recognize the octane number of the fuel but the knock sensor on the engine can. Higher octane number delays the ignition compared to lower octane number. If one use regular (87octane) fuel the knock sensor gives the data to ecu and ECU switches the timing to prevent it. So, irrespective of sport mode on or off it's all the data recorded by the sensor and feeding it to ecu.
 
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amirza786

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Just to be clear, there is no Gas Octane detector in the CIVIC that will automatically switch the ignition timing ?

The switch of the timing is done manually by the driver, by switching the car between Normal & Sports.

So,
(1) to prevent Pre-Ignition, the driver is responsible to make sure that they do NOT select SPORT mode (ie Sports ignition timing) with Low Octane Fuel ?
(2) If the driver select Normal, and used Premium High Octane fuel, they will get no benefit, and just be paying for more expensive gas, giving them the same MPG as the lower octane fuel. ?
As @saiko21 said, the knock sensor will report knock count to to the ECU which in turn will pull timing. It's best to use minimum 91 even if stock, although 87 won't hurt anything except some performance hit. If you are tuned, 91 and up is most likely mandatory
 

A2typeR

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I use to run 93 octane in my 2017 GTI, with a tune it was fast.

Now, I changed and sold the tuner and started running 87 octane and noticed a pretty significant difference on my butt dyno. The difference between 93 and 87 on that car was pretty high, VW recommends premium but the dealers fill it with regular lol, cheap bastards.

I would imagine 93 would add a bit of WHP/WTQ over 91 but you probably wouldn’t be able to tell without having it dynoed and even then dynos are notoriously different location and altitude etc

I’m sure a qualified tuner has seen differences between 91 and 93.

The other thing is fuel as well, some places will have accurate octane ratings and others have lower standards of the fuel and it’s actual quality.
 

thebutcher

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I have a question on the higher premium gases. At a station I go to, it says next to the 91 sticker that it is non-oxygenated. Is all premium non-oxygenated?
 

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I have a question on the higher premium gases. At a station I go to, it says next to the 91 sticker that it is non-oxygenated. Is all premium non-oxygenated?
That means it doesn't contain any additives like ethanol. And actually our turbos like ethanol.
 


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amirza786

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I have a question on the higher premium gases. At a station I go to, it says next to the 91 sticker that it is non-oxygenated. Is all premium non-oxygenated?
I believe the difference between oxygenated and non oxygenated fuel is one has ethanol as an additive. Oxygenated fuel is supposed to reduce hydrocarbons
 
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amirza786

amirza786

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That means it doesn't contain any additives like ethanol. And actually our turbos like ethanol.
You beat me again! Damn, I have to type a lot faster
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