Anyone use regular gas in their Si?

Dharmaboy

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Likely has nothing (or very little) to do with octane. Seems like Honda is doing some stuff with the valve angles and overlap to allow some fuel to spray the backside of the valves.
sweet. Guess all we have to worry about is oil dilution and swapping out the oil ever 3-5k Miles



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amirza786

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sweet. Guess all we have to worry about is oil dilution and swapping out the oil ever 3-5k Miles
Just follow the MM. Oil analysis on my last change after 7K of hard driving showed that I could have waited past 8K. Changing your oil every 3 to 5K is unnecessary, wasteful to the environment and doesn't help your wallet
 

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The answer depends. Do you believe in the scientific method? Than the answer is no. Do you believe in opinion or what your gut tells you? Than the answer is yes

Personally I would use 91 because you do get better performance, and it is recommended
Please explain more . What scientific method or opinion ?
 

amirza786

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Please explain more . What scientific method or opinion ?
Sure, let me start with the question: Would it be bad to go back and forth between 87 and 91? The scientific answer is NO. The reason is that 1) Premium is recommend and not required for this car and 2) when using Regular or Premium, the cars ECU will adjust timing based on what type of gas has been added in the tank by either pulling or advancing timing. This is documented, and I have seen it myself in data logs from when I did runs. You would see this under knock control or k.control. The reason for this is 87 octane is more volatile and can pre-ignite causing knock or ping in higher compression/turbo charged engines

An opinion would be making the statement that switching between 87 and 91 is bad, the reason being is first of all its not correct and secondly there is no data to support that, from Honda or anywhere else. The person feels for whatever reason that switching back and forth would hurt the car without actually experiencing it being damaged.

That being said, Premium is the recommended fuel, the car will perform better on it, and you will get 15 more hp, which is a good reason to use it.

One caveat I would like to point out is if you are tuned, that changes the equation, as in most cases the car was specifically tuned for premium (Ktuner base maps, TSP Stage 1 tune etc)
 
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Jolavemma

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Sure, let me start with the question: Would it be bad to go back and forth between 87 and 91? The scientific answer is NO. The reason is that 1) Premium is recommend and not required for this car and 2) when using Regular or Premium, the cars ECU will adjust timing based on what type of gas has been added in the tank by either pulling or advancing timing. This is documented, and I have seen it myself in data logs from when I did runs. You would see this under knock control or k.control. The reason for this is 87 octane is more volatile and can pre-ignite causing knock or ping in higher compression/turbo charged engines

An opinion would be making the statement that switching between 87 and 91 is bad, the reason being is first of all its not correct and secondly there is no data to support that, from Honda or anywhere else. The person feels for whatever reason that switching back and forth would hurt the car without actually experiencing it being damaged.

That being said, Premium is the recommended fuel, the car will perform better on it, and you will get 15 more hp, which is a good reason to use it.

One caveat I would like to point out is if you are tuned, that changes the equation, as in most cases the car was specifically tuned for premium (Ktuner base maps, TSP Stage 1 tune etc)
good to know ! Thank you very much for taking the time to explain it brother
 

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j9lazur

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Required fuel is regular unleaded with premium recommended. So using regular fuel won't void the warranty, but it'll pull timing and cut power to adjust for the different fuel. Basically with the Si (and Type R), the engine is designed to run on premium, but can run on regular as well with an ECU that will adjust timing for the fuel that is in it.
I'm a new 2020 Si owner and am still on my first tank of gas. I found this old thread and want to add new info with this screen grab from the 2020 manual. It's similar to what has been said but a little more specific. If your car has sport mode, which the Si does, the manual is specifically recommending 91 octane or higher and cautioning against anything less than 87. Of course, if you never use sport mode, perhaps not an issue. Dunno.

Screen Shot 2019-12-29 at 8.08.23 PM.png
 

tinyman392

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I'm a new 2020 Si owner and am still on my first tank of gas. I found this old thread and want to add new info with this screen grab from the 2020 manual. It's similar to what has been said but a little more specific. If your car has sport mode, which the Si does, the manual is specifically recommending 91 octane or higher and cautioning against anything less than 87. Of course, if you never use sport mode, perhaps not an issue. Dunno.

Screen Shot 2019-12-29 at 8.08.23 PM.png
The sport mode designation is talking about cars with sport mode vs sport mode itself (note how they say models with sport mode vs just sport mode, they are referring to the model vs the mode). So if you have a car with sport mode, then they recommend 91, minimum is 87, and anything lower than 87 can cause damage to the motor. The mode you're driving the car in doesn't matter in this case, it's the fact that it has the mode available. IE, if you're driving in normal mode using 85, you can damage your motor, but 91 is still recommended in normal and sport modes. I'm assuming they are using the sport mode designation to group together the following trims: Si coupe, Si sedan, Sport coupe, Sport Touring coupe, Sport sedan, and Sport Touring sedan instead of listing those 6 outright.

TL;DR: The sport mode is used to indentify the model/trim of the vehicle not referring to the mode itself, rather a car having said mode. Using < 91 octane in normal mode may still cause knock, using < 87 octane in normal mode will cause damage.
 

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Dealer put in regular on my first tank. Ran 89 midgrade for my 2nd/3rd tanks, and then just started to run premium on my 4th (current) tank after noticing the prices come down.

I'll just say that I notice a decent difference between when I got the car with regular and on this tank with premium gas that I put in. It feels smoother and throttle response I find is a bit better.

So as long as prices are reasonable, I will always put premium in. It's good to know (and I confirmed with dealer along with my manual) that running regular is fine if I have to though.
 

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The sport mode designation is talking about cars with sport mode vs sport mode itself (note how they say models with sport mode vs just sport mode, they are referring to the model vs the mode). So if you have a car with sport mode, then they recommend 91, minimum is 87, and anything lower than 87 can cause damage to the motor. The mode you're driving the car in doesn't matter in this case, it's the fact that it has the mode available. IE, if you're driving in normal mode using 85, you can damage your motor, but 91 is still recommended in normal and sport modes. I'm assuming they are using the sport mode designation to group together the following trims: Si coupe, Si sedan, Sport coupe, Sport Touring coupe, Sport sedan, and Sport Touring sedan instead of listing those 6 outright.

TL;DR: The sport mode is used to indentify the model/trim of the vehicle not referring to the mode itself, rather a car having said mode. Using < 91 octane in normal mode may still cause knock, using < 87 octane in normal mode will cause damage.
@tinyman392 thx, makes sense--there's a manual for sedans and one for coupes, each including all trim levels
 

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The sport mode designation is talking about cars with sport mode vs sport mode itself (note how they say models with sport mode vs just sport mode, they are referring to the model vs the mode). So if you have a car with sport mode, then they recommend 91, minimum is 87, and anything lower than 87 can cause damage to the motor. The mode you're driving the car in doesn't matter in this case, it's the fact that it has the mode available. IE, if you're driving in normal mode using 85, you can damage your motor, but 91 is still recommended in normal and sport modes. I'm assuming they are using the sport mode designation to group together the following trims: Si coupe, Si sedan, Sport coupe, Sport Touring coupe, Sport sedan, and Sport Touring sedan instead of listing those 6 outright.

TL;DR: The sport mode is used to indentify the model/trim of the vehicle not referring to the mode itself, rather a car having said mode. Using < 91 octane in normal mode may still cause knock, using < 87 octane in normal mode will cause damage.
The Sport Sedan/Coupe do not recommend premium and are only required to use 87/regular gas. The only "Sport" designated Civic that recommends premium are the Sport Hatches. And also there is no such thing as a Sport Touring Coupe/Sedan, its just the Sport.
 
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REBELXSi

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8 pages on this topic :rofl:
 

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