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This would be a loaded topic. Did you join just to ask that question?

Hyundai ECU doesn't adjust very widely for octane, unlike many automakers'. Anecdotally, I've noticed more consistent power delivery on midgrade (89) but not additional performance nor should you expect additional performance.
 

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Discussion Starter #3
I joined because I’m a new owner of a 2020 Elantra GT N line, I was just curious what every body else ran. I live in Colorado so the regular gas is 85 octane, I’ve been using 87 (mid grade out here) and just wanted to know if there was a difference with premium to mid grade. I wasn’t looking for performance with octane difference, just seeing if it was possibly more smooth with premium.
 

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Mid-grade to most of the country is 89 octane. I know 85 octane is typical at elevation in Colorado but I would not run it in a car equipped with a turbo. The manual specifies 87 or greater. No allowances are made for elevation. I typically run 87 from Costco. I think I ran one tank of 91 and detected no improvement.
 

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It is amazing to me that a boosted 1.6L car can even run on 87 craptane and still make 200+ hp.
Only ones that might take advantage of 91+ oct fuels are those running more boost via a tune or turbo upgrade
 

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A higher octane does not mean the fuel is more powerful. Octane rating in gasoline is fuel's ability to resist engine knock (pre-ignition). Premium fuel however does contain more energy per unit in general because it usually has zero ethanol.
 

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Not in Kalifornia....Our 91 oct has 10% ethanol due to it's oxygenation properties. The power from the higher octane is attributed to the fact you can run more boost and timing.
My Fiesta ST ran on 91 oct and was able to generate substantially more torque. I later tuned it on an E30 blend and it was a little rocket.
 

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A higher octane does not mean the fuel is more powerful. Octane rating in gasoline is fuel's ability to resist engine knock (pre-ignition). Premium fuel however does contain more energy per unit in general because it usually has zero ethanol.
Many places, premium fuel does have ethanol. Here, you need "recreational fuel" to have zero-ethanol premium. This gasoline is intended for boats, but also commonly used in lawnmowers and snowthrowers because its usually kept longer, and doesn't have the risk of varnish (which can clog up a carbureter) that ethanol fuel does. Our highest octane gasoline here is 93 in the Upper Midwest; it's not necessarily ethanol-free.

Ethanol has less energy, but higher octane. With higher octane comes the ability to design a higher compression ratio engine around it, which is one of several reasons it is used as race fuel.


As for what I use, I do use regular 87 octane gas. However, I did note Hyundai's own manual mentioning using Top-Tier additive gasoline, and have paid attention to station chains that use it (example: all Meijer store gas stations use Top Tier). I also run some STP Fuel System Cleaner every 5,000 miles, which adds detergents, and kerosene (they say "jet fuel"; pretty much the same) - it burns hotter and can remove deposits from within the engine.
 

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E-85 provided not only high compression cars with a cheaper fuel alternative but boosted cars even more benefit.The cooling properties that ethanol provides is huge. Suppresses detonation well and allows more timing and boost. I started using it when it was first available in my Evo. Beat paying $8.00 a gal for 100 oct fuel that didn't provide the gains e-85 did. Mileage does decrease but if tuned for it is not bad. I really did not care considering the power gains it provided. I ran e30 blend in my Fiesta ST for years. Ethanol is not as corrosive as methanol which is. Like I said I ran it in both vehicles for years without a problem. Car manufactures know now a days ethanol is in most fuels and make the fuel systems with materials that can comply with it.
 

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Mid-grade to most of the country is 89 octane. I know 85 octane is typical at elevation in Colorado but I would not run it in a car equipped with a turbo. The manual specifies 87 or greater. No allowances are made for elevation. I typically run 87 from Costco. I think I ran one tank of 91 and detected no improvement.
I also use Costco 87. If I'm traveling I get BP or anything Top Tier. I did accidentally get Premium 91 once and didn't notice any difference.
 
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