Octane ratings

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Hey Everyone,

Last year I switched my car over from 87 to 93 octane. According to Hyundai the ECU can adapt to higher octane fuel and allow the motor to produce up to 10 more horsepower.

The manual reads:

"Your new vehicle is designed to use only
unleaded fuel having a pump octane
number ((R+M)/2) of 87 (Research
Octane Number 91) or higher."

I was running 87 for 15,000 miles and didn't have any problems. Now, the reason I switched is because many people recommend higher octane fuel for turbo cars. But now I'm wondering if I'm just wasting my money at the pump. I've seen some dyno charts that show decreased power on 87 but I've also seen good runs on the same octane as well.

So I guess the question is, should I continue to use 93 or switch back to 87?

-Thanks
 
Hello Swift,

Our 2.0T runs completely fine on 87 as well. But it has only had one or two fill ups with that octane (when the wife fuels up), i mostly use 93. I'd rather use the octane to keep the pings at bay vs the computer which i'm beginning to feel is completely irrational based on my wife's fill-ups. At first, i thought i noticed a difference in MPG but resigned myself to the fact that too many variables are involved to accept any fractional gains or losses. But i'm sure most folks use the 87 without a thought or worry.
 
To make things more confusing check out these two different webpages from the Hyundai website.


1. http://www.hyundainews.com/us/en/media/pressreleases/33808

They claim "With the 2.0-liter Theta II turbocharged GDI engine, the 2012 Sonata offers an unprecedented combination of segment-leading fuel efficiency and power – with a 34 mpg highway rating, 274 horsepower at 6,000 rpm and 269 lb-ft of torque from 1,800 - 4,500 rpm with regular fuel."

2. https://www.hyundaiusa.com/about-hyundai...G-20120214.aspx

I know it's a different car but it's the same engine, they claim the genesis 2.0T makes 274hp on premium gas and 260hp on regular.
 
Did you notice any difference in driveability or fuel economy when you switched to 93? On a turbocharged gasoline engine, I wouldn't run anything less than 91 (R+M)/2. In the long run, I think it would be better for the engine.
 
I'm assuming as 87 is approved, there's no pinging in your use. But if you use more than 75% throttle and 75% of redline rpms in a regular basis, you should run 93, for safety sake. Now if less than 75% in both throttle plate and max rpms, than use 87. That higher output where the real enrichment needs occur, to avoid harmfull detonation or even internal parts overheating, from EGT, like exhaust valves and piston crown.
Not whithstanding the injection self regulation program on mixture, my theory is parallel on agressive leaning technics procedures, in mixture controlled engines. Hardly fuel related harm below 75% power. It is the last 25% of peak cylinder pressure, that really call for efforts and the injection system start to shove fuel to compensate for octane and cc cooling.
 
Originally Posted By: Swift101
To make things more confusing check out these two different webpages from the Hyundai website.


1. http://www.hyundainews.com/us/en/media/pressreleases/33808

They claim "With the 2.0-liter Theta II turbocharged GDI engine, the 2012 Sonata offers an unprecedented combination of segment-leading fuel efficiency and power – with a 34 mpg highway rating, 274 horsepower at 6,000 rpm and 269 lb-ft of torque from 1,800 - 4,500 rpm with regular fuel."

2. https://www.hyundaiusa.com/about-hyundai...G-20120214.aspx

I know it's a different car but it's the same engine, they claim the genesis 2.0T makes 274hp on premium gas and 260hp on regular.


Sonata is GDi / Genesis Coupe is MPi
 
No, they give two numbers (R+M/2) is not really an octane value, but the average of the Research Octane Number (RON) and the Motor Octane Number (MON). IIRC, this is called the Anti Knock Index or AKI

So you have to have a fuel that has an AKI of 87 or over where the RON value is 91 or over.

I don't know how you can find the RON value as I've only observed AKI values on the pump.

Originally Posted By: Tegger
Looks like Hyundai's own manual contradicts Hyundai itself...?
 
Originally Posted By: javacontour
No, they give two numbers (R+M/2) is not really an octane value, but the average of the Research Octane Number (RON) and the Motor Octane Number (MON). IIRC, this is called the Anti Knock Index or AKI

So you have to have a fuel that has an AKI of 87 or over where the RON value is 91 or over.

I don't know how you can find the RON value as I've only observed AKI values on the pump.

Originally Posted By: Tegger
Looks like Hyundai's own manual contradicts Hyundai itself...?


+1
 
93 Octane feels more punchy but it could all be in my head. I go WOT probably 2-3 times per week so I guess I better keep using premium.
 
Nobody can help you make that decision. Do you want more HP, save money, improved fuel economy, what?
 
And to correct my typo, (R+M)/2 not how I wrote it in my other post.

Originally Posted By: javacontour
No, they give two numbers (R+M/2) is not really an octane value, but the average of the Research Octane Number (RON) and the Motor Octane Number (MON). IIRC, this is called the Anti Knock Index or AKI

So you have to have a fuel that has an AKI of 87 or over where the RON value is 91 or over.

I don't know how you can find the RON value as I've only observed AKI values on the pump.

Originally Posted By: Tegger
Looks like Hyundai's own manual contradicts Hyundai itself...?
 
Originally Posted By: Swift101
Hey Everyone,

Last year I switched my car over from 87 to 93 octane. According to Hyundai the ECU can adapt to higher octane fuel and allow the motor to produce up to 10 more horsepower.

The manual reads:

"Your new vehicle is designed to use only
unleaded fuel having a pump octane
number ((R+M)/2) of 87 (Research
Octane Number 91) or higher."

I was running 87 for 15,000 miles and didn't have any problems. Now, the reason I switched is because many people recommend higher octane fuel for turbo cars. But now I'm wondering if I'm just wasting my money at the pump. I've seen some dyno charts that show decreased power on 87 but I've also seen good runs on the same octane as well.

So I guess the question is, should I continue to use 93 or switch back to 87?

-Thanks


What is your goal? Maximum HP or less expense?

A dyno will tell you if you are getting more power from higher octane; as many have pointed out on here, your butt dyno is subjective.

As far as being safe at a certain throttle setting, we can be certain that the engineers made it safe at 87. Some turbos require higher octane but yours obviously doesn't.

There are lots of engines where 87 is fine, but in order to get maximum power, 91 or even 93 is required - hence the notes in owner's manuals recommending higher octane when towing or in mountainous regions, for example.
 
Last edited:
But with just 2 or 3 WOTs a week, you can be sure the engine will outlast the frame ... The safety issue is usually for some of more abused engines wich may in eventuality of loosing a knock sensor, need A.K. capability. Other than that the injectors will shove up some excess fuel to keep things cool and under control. And that's about 2 table spoon of excess fuel for every WOT you give. Not to worry in your scenario with 87AKI all the time.
 
(Don't know why you're top-posting, but OK...)

This thread has nothing to do with Research vs Motor vs AKI. It has to do with an apparent contradiction in the OP's original post.

This is what the OP said originally:
"According to Hyundai the ECU can adapt to
higher octane fuel and allow the motor to
produce up to 10 more horsepower...
The manual reads: 'Your new vehicle is designed
to use only...a pump octane number ((R+M)/2) of 87...'"


This implies that there is documentation OTHER than the manual which is quite specific in promising an "up to 10" hp increase with the use of higher octane. I would like the OP to tell us where the "up to 10" hp promise comes from.


Originally Posted By: javacontour
And to correct my typo, (R+M)/2 not how I wrote it in my other post.

Originally Posted By: javacontour
No, they give two numbers (R+M/2) is not really an octane value, but the average of the Research Octane Number (RON) and the Motor Octane Number (MON). IIRC, this is called the Anti Knock Index or AKI

So you have to have a fuel that has an AKI of 87 or over where the RON value is 91 or over.

I don't know how you can find the RON value as I've only observed AKI values on the pump.

Originally Posted By: Tegger
Looks like Hyundai's own manual contradicts Hyundai itself...?
 
Originally Posted By: Swift101
Hey Everyone,

Last year I switched my car over from 87 to 93 octane. According to Hyundai the ECU can adapt to higher octane fuel and allow the motor to produce up to 10 more horsepower.

The manual reads:

"Your new vehicle is designed to use only
unleaded fuel having a pump octane
number ((R+M)/2) of 87 (Research
Octane Number 91) or higher."

I was running 87 for 15,000 miles and didn't have any problems. Now, the reason I switched is because many people recommend higher octane fuel for turbo cars. But now I'm wondering if I'm just wasting my money at the pump. I've seen some dyno charts that show decreased power on 87 but I've also seen good runs on the same octane as well.

So I guess the question is, should I continue to use 93 or switch back to 87?

-Thanks
This is true for their turbos. My Gen Coupe manual says the same thing and it is show to be true on the dynos. Or just watch your timing at WOT as it does not retard as much.

And really it is not so much WOT but the rpm you are at and throttle angle. Low rpms and big throttle angles will really bump up the absolute load. With a turbo 300% is not out of line when just under the peak torque rpm.
 
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