Super Unleaded test compared to Regular Unleaded:

[daviderle]

I have been trying to resist the urge to comment on this subject, but this thread seems to have few misconceptions and we do not appear to get to any reasonable conclusion, therefore, it may be a good time to quote (somewhat) a reliable reference:

"Octane rating or octane number is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance petrol engines that require higher compression ratios
....
Petrol engines (also referred to as gasoline engines) rely on ignition of air and fuel compressed together as a mixture without ignition, which is then ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for petrol engines. Use of petrol (gasoline) with lower octane numbers may lead to the problem of engine knocking".

So, in the Genesis case, the use of low octane is less of an issue in the Pre MCE (2009-2011) MPI engines, while the 2012-2015 GDI engine may present a bit more of a challenge due to the higher compression ratio (which resulted in the higher HP/TRQ numbers). The engine timing can indeed adapt in both cases, but I personally find the knocking and the black soot on the back bumper is too much in order to save few dollars in my R-Spec, while I am happy to use regular 87 most of the time in the 4.6 2009.

Hence, my personal conclusion: there is enough evidence to go either way, so it seems this thread maybe more of a personal preference than a technical discussion..


Reference: http://en.m.wikipedia.org/wiki/Octane_rating

 

[jimb100]

Premium Extra energy? Not really. I posted this link much earlier but as I read recent post It appears that some people here did not read it. It explains octane and knocking etc.

http://www.economist.com/blogs/babbage/2012/09/octane-ratings

So its not extra energy in the gasoline its the extra anti knock compounds in premium that allow higher compression and thus better fuel economy.

Sounds like you do get more MPG from premium on higher compression engines.

 

[powerslide]

I am driving the right car. I don't car about fuel economy. I am simply interested in seeing if there is an added benefit using Super Unleaded -vs- Regular Unleaded.

I gave fuel economy up when I traded in my 2002 Honda Civic SI which got 30mpg over the past 10 years...

I know you are and i appreciate the study you have shared. The discussion seemed to be turning into a back and forth on fuel economy of big engined luxury sedans.

 

[BrazGenesis]

Given the price of the car, the extra money spend w/gas should not be the real concern.
Protecting the engine seems relevant. It is also expensive and even reducing cleaning operations (with a premium aditive mix) may be a good way to go.

Years ago I read something that 10:1 compression ratio was the breakeven between premium and regular. At the same time I read that a microphone placed in the modern engines "hears" the knoking caused by low octane and command an ignition point delay to eliminate it. In this case SOME loss of performance could occur.
I can't comment on the points above Vs the current GDI engines, that seem more critical on the item cleanliness.

Based on this I opted for the very best gasoline for my 2012 3.8.
In summary: more peace of mind and my toy feels happier.

 

[PMCErnie]

Behind every car owner who claims he/she doesn't care what something costs is a life partner who says, "You paid WHAT for that?!?!?!"

 

[AuToMoSeS]

Without knowing the Butane level added to the fuel, it's nearly impossible to compare fuels with consistency. My mileage various as much as 15% from tank to tank, brand to brand with consistent driving trips. Read this article, you may be surprised.

http://www.technicsglobal.com/butane_blending.html

 

[homeofstone]

Behind every car owner who claims he/she doesn't care what something costs is a life partner who says, "You paid WHAT for that?!?!?!"

Maybe that's true for most average income households but not for many of the top 1% of incomes. I know too many where for instance going shopping in Italy for a long weekend is done without a thought of cost. I think the point was that if you buy a new large sedan that recommends premium gas then why worry so mush about cost of gas. If a person's budget is so tight that a few hundred dollars extra on gas cost in a year or insurance cost is really important to being within their means then they should have never purchased such an expensive car.

 

[mikec]

Thermodynamic efficiency of a 4-stroke gasoline engine is a function of the compression ratio. It is not a linear relationship though. Going from 6:1 to 7:1 compression ratio makes a big difference in efficiency... going from 7:1 to 8:1 is a smaller improvement. By the time compression ratios get to the 10:1 or 11:1 area the gains are smaller and smaller - diminishing returns. The gains at modern compression ratios though are still worthwhile - especially given the regulatory standards for CAFE (MPG requirements) and emissions.

Compressing the air+fuel mix in the cylinders, as the piston rises on the compression stroke, also increases the temperature of that air+fuel mix. That's one of the laws of thermodynamics. Folks with air compressors know this too: compressing air makes it hot - check the temp in the pipe from the compressor body to the tank. Any air+gas squeezed enough will eventually self ignite from the extra heat added by compression.

In the "old" days of carbureted engines, the engine coolant circulated through the engine block first, then the cylinder head and intake manifold and to the base of the carburetor. This kept the carb warm to minimize ice formation... air flowing through a carb looses pressure - and thus cools off - so any humidity could end up as ice on cold days. Once the carb mixed the air+fuel, that mix had to flow through the intake manifold pipes to reach the cylinders... if those manifold pipes were cool enough, the fuel would condense out of the mix (like morning dew on your lawn) and thus wouldn't end up in the cylinders. Using block-heated coolant to warm the manifold reduced this problem... but it DID heat up the air+fuel mix. That had two negative side effects: 1) the air+fuel was warmer so it was less dense, leading to less potential horsepower in the cylinders, and 2) being warmer than ambient temperatures meant it just got that much hotter during the compression stroke leading to earlier knock/detonation... ergo compression ratios were limited. To avoid icing and condensation of the fuel in the manifold, carb engine cooling systems had to sacrifice some potential torque & HP and potential compression ratio. Some engines placed the intake manifold on top of the exhaust manifold so the hot exhaust could keep stuff warm... instead of using engine coolant. Same side effects though.

Once port fuel injection was everywhere (pretty much forced by emissions regulations - carburetors could not be precise enough) the issue of the fuel condensing out of the air+fuel mix in the intake manifold was gone - as there was no fuel in the bulk of the manifold. So the need to heat the manifold was reduced considerably. Eventually car makers "caught on" and changed the flow of engine coolant so that the cylinder head is cooled first, then the coolant flows into the block. This means today's cyl heads are cooler than they were in carb days. That allows a bit higher compression ratio before the critical self-igniting temp is reached. And not having to heat the manifold meant the air going into the engine was cooler and therefore more dense so horsepower and torque increased too.

The next "step" in efficiency improvement is direct injection. If the engine compresses only air there is no chance of knock/detonation. That air will still heat up from compression but, with no fuel, nothing burns. Injecting the fuel near the end of the compression stroke shoots cool fuel into that hot compressed air... cooling it a bit. And it cools even more because the fuel evaporates - absorbing heat energy. The final temp of this now slightly cooler air+fuel mix is below what it would have been in a conventional port fuel injected engine... ergo the compression can be raised a little bit more to eek out a little more efficiency. That's why direct injection engines are 3 to 5% more efficient than their port fuel injected counterparts.

On any spark ignited gas engine, the spark does not happen at "top dead center" which is when the piston has finished the compression stroke and is ready to start the power stroke. Why? It takes a short bit of time for the "flame front" to move through the entire combustion chamber and get the air+fuel mix burning. So the spark is timed to occur prior to the end of the compression stroke so that the burn can get spread around just as the piston is ready to move downwards on the power stroke. If the air+fuel mix is almost at the point of pre-ignition/detonation, the flame front will move more quickly but much more chaotically so the timing of the spark has to be delayed a bit to make sure that chaos occurs when the piston is ready to move down. Otherwise, the force tries to slam the piston downwards while it is still moving upwards leading to knock and potential physical engine damage. This is where gasoline octane rating comes into play. Higher octane fuels allow higher compression ratios and ignition timing more suited to the time it takes the flame front to smoothly spread through the chamber. Using a low octane fuel, on an engine designed for high octane (i.e. an engine designed with slightly higher compression ratio), means the ignition timing has to be compromised (delayed). The engine will be less efficient... but will the loss in efficiency be greater than the price difference between "regular" and "premium" fuels? That answer is a "maybe" - it depends on the relative fuel prices, the "other stuff" in the fuel like the added ethanols, and one's driving style. Highway vs. stop-n-go city driving makes totally different demands on the engine. Highway driving is "part throttle" so the amount of air in the cylinders is reduced (compared to higher throttle openings needed to accelerate from red lights) so there are fewer air molecules getting compressed... which means there is "more room" for those molecules at the end of the compression stroke... ergo the final pressure is lower and thus there is far less issue with detonation. So modern engines won't have to retard spark much at part-throttle and you'll see less difference in MPG at highway cruise. Ambient air conditions play a role too: barometric pressure affects air density, ambient temperature too... both affect "when" knock/detonation will occur.

mike c.

 

[mf7lakes]

I take a 900+ mile trip (1800 miles round trip) about 2 to 3 times per year. On the way down I use 87 oct. fuel w/ethanol.

On the way back, I use 87 oct. fuel NON-ethanol.

Invariably, I get about 3 more miles per gallon with the NON-ethanol variety.

Latest trip taken between November 20th and December 2nd. Interstate highway, mostly locked down to 74 mph.

With the ethanol 87, I got 24.8 mpg. With the NON-ethanol 87, I got 29.6 mpg. I have done this 6 times over the past 2 years. It doesn't vary by much.

 

[DavidA5913]

Mikec: thank you for that explanation. Very informative.

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[BrazGenesis]

Mikec: thank you for that explanation. Very informative.

+1 - learned a lot! Thanks

 

[Mark_888]

Now why in the world would you assume that? Since us V6 owners are at a horsepower disadvantage, I'd say we'd be *more* interested in increased HP than V8 owners, whom already have enough horsepower. (Relatively speaking, of course.)

Hyundai marketing made a decision as to whether they want to advertise more HP and do EPA tests with premium, or they can have a little less HP and advertise that the car uses regular for lower cost of ownership. Since they already decided what to do in that regard (ever since 2009 Genesis), not sure what you are arguing about. Just because marketing makes a decision doesn't mean it is always correct, it just means they made a decision.

 

[Mark_888]

All the experts in "the whole wide world" say that using premium gas unnecessarily will cost you more money per mile than regular. That is what we are debating here. Those car owners who want to reduce their 0-60 time by .1 seconds are certainly welcome to pay more for that privilege. I doubt that you put premium gas in your car so, obviously, you completely agree with me on this point. Premium gas buyers, assuming the current cost differential, will always pay more to drive from point A to B.

I am not claiming that premium is cheaper. The increased MPG of premium may not offset the difference in price. I just object to those who say that all engines (and specifically the Genesis V8) will not get better HP and better MPG with premium.

 

[homeofstone]

I am not claiming that premium is cheaper. The increased MPG of premium may not offset the difference in price. I just object to those who say that all engines (and specifically the Genesis V8) will not get better HP and better MPG with premium.

+1

 

[DRS]

Even though one of these guys just died, I think the Car Talk guys are more credible on this subject.

http://www.cartalk.com/content/premium-vs-regular-0

Then there is Edmunds...

http://www.edmunds.com/fuel-economy/to-save-money-on-gas-stop-buying-premium.html

Car and Driver knows a few things about cars too.

"Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price."

http://www.caranddriver.com/features/regular-or-premium

The 5.0 IS designed for premium. AND is the recommended fuel. The articles above discuss using higher grade fuel than is recommended.

Using regular does not get the most out of the 5.0 for mileage, performance, and long term durability. If it were not for the computer and GDI, the motor would not have the ability to adjust for regular (at a lower power and efficiency).

USE premium. I do. I get 17% better mileage, it is much faster, and I know I am using the fuel that the engine is designed for (and recommended by the manufacturer.

 

[DRS]

There's your problem, Premium has no extra energy whatsoever, only difference in layman's terms is premium is concocted to reduce the volatility of the mixture. You are paying extra for premium because it takes additional refining steps to reduce the volatility, not because it is more powerful or any better. Only engines today that do require premium are of the turbo variety. Preignition sensors are quite old and I would venture to say anything 10+ years old will automatically adjust to the fuel used.



Look at it this way, most are suckers for advertising strategies and if they sold gasoline today as "gas" and "anti pre ignition gas" we would never have had the premium vs regular debate. It really is amazing what a word can put into peoples minds.

The 5.0 has higher compression and native valve and spark timing designed by the manufacturer for premium (higher octane) fuels. This translates to a higher efficiency of the premium fuel burned. When using regular which is NOT designed for the compression and timing, it generates less power off the optimum power cycle. It will detonate long before it is supposed to. The computer has to compensate for this to prevent damage and keep it running smoothly. Mainly by adjusting valve, ignition timing and the timing and amount of the GDI fuel. This lowers efficiency, lowers the power and ears up more fuel.

Back in the days off Bill Elliot supremacy, his brother Ernie designed a special higher compression combustion chamber than anyone else at the time had. This design was able to use same fuel but produce more power without detonation. The Ford head design allowed for this. Once the secret was out, others caught up. The cars had s massive increase in power and mileage on the track. So much so, that GM bigot Bill France Jr., who is pro GM, forced increased carb restrictor plates rules on the Fords to slow them down. Until GM caught up. IF lower compression and using regular fuel was the way to go, racing teams in all disciplines would have compression ratios of a lawn mower, and use 70 octane fuel. Oh, and we are NOT talking about turbo engines as someone mentioned above as the only design to use premium.

Those old coots who promote regular use for the 5.0 Genny, which is Designed to use higher octane fuel, and insist they are "right", are just wrong. The manufacture as used good computing and fuel system to adjust for places that do not have premium available. That hack prevents major problems when using a fuel under the rating that is what the engine is designed for.

 

[Midnightsun]

The 5.0 IS designed for premium. AND is the recommended fuel. The articles above discuss using higher grade fuel than is recommended.

Using regular does not get the most out of the 5.0 for mileage, performance, and long term durability. If it were not for the computer and GDI, the motor would not have the ability to adjust for regular (at a lower power and efficiency).

USE premium. I do. I get 17% better mileage, it is much faster, and I know I am using the fuel that the engine is designed for (and recommended by the manufacturer.

My manual says and yes this is for the V8. "Your new vehicle is designed to to use only unleaded fuel having a minimum octane number of 87 or higher" It then goes on to say for improved vehicle performance they recommend using 91 octane. With all due respect, saying your car is much faster is not true by any means except maybe your perception. There is just no way less than 10hp can be felt when one has over 400 already on tap. That would be like saying my car is much faster if my child is not in the car. 17% better milage? Again, with all due respect, no way!

 

[DRS]

That is what I experience.... Period... And my 2012 says designed for premium. Which it is...

If it was not, using premium would not add any performance or mileage increase. As is common with engines that have lower compression ratios, and computers, designed for regular. Adding premium will not generally increase performance or mileage.

 

[DRS]

And my increase in mileage is real. When driving for economy, lower RPMs, where detonation is at its worst (and compensation to prevent it is at a strong setting) using low octane gas, lowers the mileage as I stated. I would guess the percentage improvement closes up a bit in wide open or heavy foot driving.

As for the increase. The HP increase, torque (low end torque and mid RPM torque) is vastly increased on the street verses what the max rating published when using high octane. Why? Likely again the Lower RPM increased detonation that the computer has to adjust out.

I have not been on dyno using street profiles with both regular and premium, but suspect the output difference between low octane and high is downplayed in the published numbers for max HP.

 

[videopho]

Using premium and non-ethanol since second fill up (1st was on the dealer).
Avg: 17 cty and 28 hwy.