Best gasoline for Hyundai Elantra?

Hello All,
What is the best gasoline to use for a 2004 Elantra? I'm presently using 87 octane Mobil or Exxon and am thinking of switching to 89 octane. I just had a tune up and a fuel injector cleaning done, but,
am experiencing some pinging and engine knock on acceleration, or going up a hill. If I use a higher octane will higher burn rate hurt the cylinders? I appreciate the advice. (What if I fill half full of 87 and half full of 89 octane?)
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Fill it up. You won't hurt anything by going to 89 octane. You could burn hi-test if you really wanted to simply spend money for no reason, and still not hurt anything.
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Mike Marlow wrote:

That's not true. Slower burning high-octane fuels will not burn completely in an engine that's designed for faster burning, lower-octane fuels. The end result is poorer performance, lower gas mileage and carbon buildup in the engine.
If the OP's engine is pinging, he may have no choice other than to use 89 octane fuel, but I wouldn't go any higher than that. If the 89 doesn't stop the pinging, something else is wrong. It may indicate a sensor issue that's causing the timing to be advanced too far or perhaps the knock sensor has failed.
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Brian Nystrom wrote:

My theory is that higher octane fuel may actually be less efficient because it's still burning when the exhaust valves open -- part of the charge just blows out the tailpipe.
For the same reason, it may even lead to burned exhaust valves.
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Higher octanes have a *lower* burn rate. That's why there's less pinging.
There's no problem with using 89 Octane other than the additional money you'll spend.
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Unless you live in the Midwest, and then, due to ethanol tax credits and the like, often 89 - ethanol blend is cheaper than 87 - straight unleaded.

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Going to the higher octane may or may not stop the pinging, but it certainly won't fix the problem. It will take an extra few dollars out of your pocket every time you fill up. Maybe the guy that did the alleged tune up did something to cause the problem if it just started.
Most cars today, including the Elantra, are designed to run on 87 octane and have no gain no improvement, no benefit, when the 89 is used. Yes, you can also mix them to waste a little less money.
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