Thread: Regular/Mid/Premium...What's the Diff?

regular gas is fine . Premium supposedly gives you 4hp increase which you won't feel. Why wast your money?

I had believed it was worth 10hp?

At least on the 380 it does. It says 306hp with 87, and 316 with 91. This is of course hypothetical with very little backing.

Really, a buddy of mine and I were debating this one day (me with my GC and him with his G37S), to run premium in your car in comparison to 87, it will cost you about 200-300 bucks more a year (this of course depends on the mileage you drive a year, so it will vary slightly). Think of the little things you piss 200 bucks away on. If you like your car feeling slightly better, and you feel its better for your car, its not going to kill you too much to run premium in a period of a year.

the 200T it's supposedly worth 11hp, but it's much more worth it in gas milage. But turbo cars usually like higher octane for everything.

I know our Speed6 calls specifically for Premium for the turbo.

i'm not sure if the same applies to other areas (pretty sure tho), but now gas from 87-91 octanes contain as much as 10% ethanol in all gas stations around where I live, which is supposed to help with both performance and mileage because of the ethanol itself containing oxygen. mileage? that makes sense. performance? i dunno.

anyway, i think the 3.8 won't go much faster with higher grade octane because it's naturally aspirated. the 2.0T, however, will because the turbocharger forces more air into the engine and increases performance. as mentioned somewhere above, the higher grade octane will make the car's ecu more stable, but also taking the bmw x5 as an example, it drinks 91 because of the fact that when air is forced into the engine, the temp is warmer and with lower grade octanes, it will for sure mess up the engine. (in the worse case the engine will blow i think? dunno have to google on that)

correct me if i'm wrong but that's my interpretation from books about car mech that i've read in the past.

but even with higher grade octane, the 2.0T will need to be further tuned for better performance. (obviously?)

Here's a good article on gasoline...

Fact or Fiction?: Premium Gasoline Delivers Premium Benefits to Your Car: Scientific American

Basically, to sum it up, if your car is designed to use low octane fuel (which our Genesis's are) then you're wasting your money buying higher octane fuel.

I have a few issues with that article. I'll start with this:
The article makes it seem like through its writing that and Internal Combustion Engine (from now on acronymed ICE) has an explosion that drives the piston down on the 3rd stage of the Otto cycle. It doesn't, you should never have an explosion of any kind in any ICE, it's a controlled burn.
Octane ratings are a measurement of detonation resistance, to simply say that it's more "anti-knocking" at 91 than at 86 is wrong because it's only more anti-knocking under test conditions for engines designed for certain octanes.

This compression ratio—somewhere in the neighborhood of eight to one—tolerates lower octane fuels (such as regular gasoline, good old 87 octane) without knocking. "The compression ratio is fixed by the designer of the engine," Green says. "The regular fuel will burn properly and the premium fuel will burn properly and therefore there is no reason you should pay the extra money." High-performance engines, such as those in some sports cars or older, heavier automobiles, often boast much higher compression ratios. These cars—for example, Shepherd's Subaru WRX—require premium gasoline and will definitely knock without it

Given these conditions the Genesis would benefit greatly from higher octane fuel.

Hyundai's website states:
2.0TCI Compression Ratio - 9.4:1
3.8NA Compression Ratio - 10.4:1

The 3.8 is a high compression ratio engine, it tolerates regular and the computer compensates for the conditions of regular fuel by modifying anything from timing to air/fuel mixtures. Hyundai states you can use regular because a lot of people won't buy cars that need Premium or other high octane fuels.
Given that information, the 2.0T would benefit less than the 3.8 because of it's lower compression ratio.. but thats not true in real world circumstances because higher octane fuels burn longer than lower octane fuels. Meaning more and hotter gases are formed building boost which enhances scavaging.

Such high compression ratios—and the premium fuels that go with them—could be turned to efficiency, rather than speed, Green notes, especially if put into the engines of lighter cars like his Honda Civic. Other automotive fuels, such as ethanol, can also offer high octane ratings, allowing oil companies to use more volatile gasoline in such blends.

The Genesis doesn't gain a lot of power with Premium, but it does gain power. It does however in my experience gain quite a bit in fuel economy. And if you want more evidence that you probably shouldn't be using regular in your tank, check out page 3 in section 1 of your owners manual.

Gasohol, a mixture of gasoline and ethanol (also known as grain alcohol), and gasoline or gasohol containing methanol (also known as wood alcohol) are being marketed along with or instead of leaded or unleaded gasoline.
Do not use gasohol containing more than 10% ethanol, and do not use gasoline or gasohol containing any methonal. Either of these fuels may cause drivability problems or damage to the fuel system.

next time you're at the pump, check it out.. right beside the Octane 87 sticker it just might say "may contain 10-15% ethanol", which by using that fuel, you're harming your car if it's closer to that 15%. Shell V-Power or Esso Premium clearly state "contains no ethanol"

Hyundai cleverly states you can use regular gas, but they don't say you can use regular gas that contains ethanol.

I run 93 as I was already having to run it on my Speed6 anyhow. The 3.8 specs do say 306HP with 87 and 315 with 91, so clearly when you run the 87, it's detuning the timing somewhat. I believe Hyundai set it up this way so they could say the car only needs 87 unlike the other high HP V6's like Nissan's VQ engines. I don't know if there is a difference between 91 and 93, but the car does seem to like it. If your engine is a normal NA engine, then anything over 87 is a waste, but this engine clearly gains power with higher octane.

As for gas mileage, I wouldn't have bought this car if I was worried about gas mileage...lol.

Excellent Technical Dissertation as usual Snoopy!
I decided to test your assertions. First, it took a few
tanks to completely bring the octane level up to 93...
I did notice a difference in mileage and acceleration...
I do mostly high speed daily driving on a one way 30 mile commute,
travelling between 70 and 80 mph depending on traffic conditions...
sometimes the commute goes 80 miles...my best mileage with 87 octane was
25.4....with 93 octane, it is 27.9....no, it doesn't pay for the
difference in price at the pump (@20 cents/gal.) but I found
it to be an interesting if unexpected improvement....
as far as acceleration, that's much harder to measure without
a timing device, and it wouldn't be world shattering anyway,
but I have noticed a difference...not like hooking
up a bottle of nitrous, but there is definitely something more there...
All in all, my honey likes the top shelf gas, so I think I'll keep feeding
it to her....after all, she's my baby....