2011 Kia Optima SX Turbo: Not Very Picky for a Turbo

"It's one thing to offer a high-powered four-cylinder engine in place of a V6, but if owners are then forced to use premium gas the cost savings go out the window. Look for this to become a more prominent issue as more and more manufacturers adopt smaller, turbocharged powerplants. "

It's NOT an issue if potential buyers possess even the most basic math skills. Assuming the car will be driven 15,000 miles per year, and that it averages 25 mpg, it will use 600 gallons of gas. If the price difference between 87 RON fuel and 93 RON fuel is $0.22 then the added cost of using 93 RON amounts to $120 per year.
$10 per month
$2.31 per week
$0.33 per day

If an extra $10 a month is going to wreck your automotive budget I'd think that buying a new car is probably not a prudent financial choice.

+1 roadburner

additionally, higher octane fuel can yield more MPG in boosted cars. Edmunds showed us this so that $120 a year is even less.

http://blogs.insideline.com/roadtests/2011/09/2011-chevrolet-cruze-ltz-the-ultimate-hot-weather-mpg-test---regular-vs-premium.html

+1 roadburner and pengwin

Judging by the dyno and acceleration results of the Hyundai corporate 2.0T, I'd say that it would definitely benefit from some 91-93 octane gas. Reading the Hyundai and Kia owner forums, it seems as though using high octane yields power, smoothness and fuel economy benefits for this engine.

It's all fine that the motor can run on 87 octane safely, but the compromises inherent in getting a relatively high compression turbo engine running 14+ psi of boost to operate efficiently on low octane gas just don't seem to be worth the cost benefit to me. I mean, if you really want that extra hp over the NA engine and are willing to pay the acquisition premium, I'd think most would be willing to pay the small fuel premium as well - if they did the math as roadburner notes.

Currently difference is on average 8%. So using that calculation above it's $48 a year.
I still think it's nice to not have to use premium even it's only 8%.

Even though that doesn't seem much many buyers look at MPG and 8% difference in MPG they would think is big enough to prefer one over another (I doubt many do the full math anyway).

Higher octane could in some cases yield more MPG but at 8% higher cost not sure you'd get also 8% higher mpg.

Actually ignore my incorrect calculation. Difference is rather $162 a year at current gas prices at $15K miles. But look at it another way:

26 mpg combined regular equates to same cost as 24 mpg premium. Now that difference looks much bigger especially if the non-turbo gets 28 mpg. So sure it's slightly deceiving (which is why some still push gallons per 100mi).

A gas cap? Oh yeah, I forgot some cars still have those. ;)

This thing does 0-60 in 7 sec, a Camry V6 does it in 5.8 sec.
The initial I4 low torque takes a toll, as on nearly all turbo I4s.

Now, what if you get 2 mpg better economy on premium vs. regular (as some Sonata/Optima turbo owners are reporting)? You use about 7% less gas (25 mpg to 27 mpg, 15k miles/year) which pretty much makes up for the price differential. And on top of that you get improved performance and reduced stress on the engine.

Another interesting feature -- the TF on the door is actually the company's code name for this generation Optima.

"It's NOT an issue if potential buyers possess even the most basic math skills. Assuming the car will be driven 15,000 miles per year, and that it averages 25 mpg, it will use 600 gallons of gas. If the price difference between 87 RON fuel and 93 RON fuel is $0.22"

It becomes an issue if you knew not everyone pays such a small premium for premium. We pay over 50 cents a gallon extra for 91 octane. I don't even want to check 93.

I'd prefer a V6 that runs on regular in a large car like this. Turbos are great for small car where V6 don't fit.

"It becomes an issue if you knew not everyone pays such a small premium for premium. We pay over 50 cents a gallon extra for 91 octane. "

600 X $0.50 = $300, or...
a whole eighty-two cents per day!!!
$5.77 per week!!!
Wow, that IS an issue!!!

It is when there's an alternative that lets you grab the $1.30 /litre pump instead of the $1.44 /litre pump... and I drive a lot more then 15K a year.

A small turbo engine in a large car only works for marketing to show good EPA numbers.

Another brilliant set of responses to a non issue!
First off, premium gas is NOT a power booster, it's an anti-knock rating. It is higher to reduce the natural volality of gasoline under higher temps and pressures.
The Optima 2.0T was designed to run at lower combustion chamber pressures and temps as a compromise between performance and low emissions.
The computer doesn't use premium slower then regular, in fact due to its higher volality restriction, you may use more, especially in cooler temps. The only exception is under extreme atmospheric temps or pressures.
People using premium are not getting better performance or mileage, in fact we're seeing reports of lower mileage.
But hey it's your money, waste it as you see fit.
When gas goes up past $4.50/gal, you enjoy spending another $.40/gal to satisfy your false beliefs. I'm sure the oil companies will be thrilled to take it.
Instead of speculating, why not ask someone who owns one, it's usually a smarter path to get answers.

Basic engine theory 101 optimasx

While 87 octane may contain slightly more BTUs per gallon than 91 or 93 octane, the issue isn't how much energy the fuel contains (the difference is very small), but how efficiently the engine can combust it.

If you're producing a certain amount of torque from a particular sized engine you're going to be producing the same average cylinder pressure regardless of the octane you're running. The problem with running low octane fuel in a high boost turbo engine is that you can't run it at optimum ignition timing, or even optimum fuel mixture in many cases. The lower octane tuneup will require that you run less ignition timing for a given load level (to avoid knock) and may also require you to run a richer mixture for that same load level. Running rich and/or retarded increases the BSFC (brake specific fuel consumption) of the engine - retarded ignition means you don't extract as much heat energy from each combustion event and waste more of it heating the exhaust and coolant, and running rich means your combustion temperatures drop, again reducing your efficiency. Remember that a internal combustion engine is a heat engine - now look up the fundamental determinants of heat engine efficiency.

Furthermore, when running higher octane fuel, the engine can produce more power for a given load level. That means that to accelerate at less than peak acceleration requires less engine load (this can go either way efficiency wise). But in the case of a turbo engine, less boost may result in less backpressure (the turbo isn't working as hard) and improve efficiency.

So, higher octane allows more ignition advance, a leaner mixture, less boost and more overall thermodynamic efficiency. If you're at full throttle all the time, you won't necessarily see any improvement in fuel efficiency, but under normal driving conditions, you can. Hence the reports of improved economy from Hyundai and Kia forums (and there have been many), along with the results of testing here on the Cruze turbo.

Next time you might want to save the snark....

Hey church,
Your forgetting a couple of things her.....
First off, your working with a DGI ENGIND, not some slush box from the 60's, or most V6's today
Second, you've got a computer which, along with a variety of sensors, provides optimum timing and spark ignition, based upon load, temp, ATM pressures and, let's not forget, it's designed to run on 87.
Again, you seem to be under some misguided presumption, that this engine, can do more than the computer parameters allows.
Again, and maybe I need to say it slower, higher octane gasoline does NOT improve performance in this engine. You want to reprogram the computer for premium, go ahead, but just putting it in this engine is a waste of money, EXCEPT, as I said earlier, under EXTREME TEMPS and PRESSURES!
I'd suggest reading up on how a GDI engine differs from any other type of induction engine, and the compromise/relationship between PERFORMANCE and EMISSIONS.
Then tell me how there's a free lunch, cause you won't improve hp, and may increase emissions using your argument.
You just dont need a higher octane fuel with this engine, it's a total waste of money.
As for snarky comments, based upon the crap I've seen put in here, not sure why all these Toyota people seem to feel a need to talk smack. It's not our fault they spent more and bought less. ;)

"Next time you might want to save the snark..."

That's apparently impossible- at least when one is such a knowledgeable expert.

"Again, you seem to be under some misguided presumption, that this engine, can do more than the computer parameters allows."

I suspect that you don't realize that you are bringing a dull butter knife to a thermonuclear exchange...

"It is when there's an alternative that lets you grab the $1.30 /litre pump instead of the $1.44 /litre pump... and I drive a lot more then 15K a year."

I drive more than 15K per year as well, but the fact that my MS3 work/snow beater is not encumbered by a car loan impacts my overall operating expenses to a much greater degree than the sled's appetite for 93 RON fuel.

I'm not forgetting any of that optimasx, and you seem to lack a fundamental understanding of modern engine management technology and strategies (along with ignoring both Hyundai's own comments about improved power and torque on 91 octane).

It just so happens that I work on engine management systems for a living. I deal with direct injected engines, turbocharged engines and people running crappy gasoline all the time. I've been doing it for over a decade and have worked on the engine management systems from virtually every manufacturer out there with the exception of some rare exotics (no Bugattis, Paganis, etc.)

Let's shed a little light on the subject, shall we? Virtually every modern engine uses an ignition strategy that is determined by a number of factors, but primarily by load (pressure/mass air flow), engine speed and air temperature. Additional ignition timing modifiers are usually put in place for lambda target (air fuel), coolant temp (heat transfer from cylinder head to intake charge), and a few other minor variables (throttle tip in for one). But underpinning the timing value selected using these variables are two limiting factors - the optimal or maximum timing map (which provides a theoretical optimum timing when not octane limited - any more would lose power even if knock was not a problem) and a knock modifier value.

The optimum or maximum timing value (GM ECUs often call it Timing for Maximum Torque) can be determined by feeding the engine a fuel with enough knock resistance to avoid detonation under any conceivable operating condition. This allows the calibration engineers to advance ignition timing until power stops increasing and begins to drop. Next, you've got to tune the engine for safe operation on its target fuel. In the case of the Hyundai corporate 2.0T GDI, that is 87 octane. So the calibration engineers now start characterizing the engine on 87 octane fuel to determine a safe timing curve.

On pretty much any engine these days running high compression, boost, or both you aren't going to be able get to your optimal timing curve even on 91 octane. Hyundai runs a average to slightly below average compression ratio for a GDI turbo engine (9.5:1), but they also shove 15-16 psi of peak boost in there. This engine is actually averaging higher cylinder pressures (more torque/cylinder) than a BMW N54/N55 6cyl turbo which only runs about 10 psi of boost peak, has 10.2:1 compression and uses 91+ octane. This tells us that the 87 octane timing curve for the 2.0T GDI has to be far, far under the ideal timing curve. And, if you look at dyno plots of the 2.0T GDI, you'll see that it doesn't run stoichiometric mixtures at full throttle for very long either (but the N54/N55 do, or VW's 2.0T), probably because that would boost cylinder temps too high for safe running on 87 octane.

The other value we have to consider is the knock modifier. This can be called different things too - knock index, knock advance multiplier, ignition advance multiplier, etc. This is a value that is determined by looking at how much knock the engine is experiencing and then using a calculation to create a moving average of sorts. The more knock you experience the more it moves from the ideal. Sometimes this modifier can be used to add timing to a base "safe" timing curve (Subaru does this by taking a value from the safe curve, then taking the ignition advance multiplier or IAM, which varies from 0 to 1 where 1 is no meaningful knock activity, and then multiplying a knock advance table by the IAM and adding the final value to the base timing.) In other cases, the knock index will go up with knock activity and be used to multiply a knock retard number to reduce timing from an optimal map (Honda does this).

There are a dozen different ways of doing this, but the end result is pretty much the same. You characterize the engine at two extremes of fuel quality (and sometimes in between). You monitor the knock sensor closely and use it to pull out timing in the event of dynamic knock events (burst knock, feedback knock, etc.). You take what you learn from the dynamic knock and use it to determine where on your bounded ignition maps you should be operating. Even without fully decoding the Hyundai ECU, I can tell you that this is how they must operate. Because if they didn't, there is no way to gain power with higher octane fuel as the 2.0T GDI does. Hyundai has made this claim to the press as well as to Hyundai owners on forums and such. The only way for any engine to gain power on higher octane fuel is to use a bounded knock strategy because I'm not aware of any car out there that is actually capable of _directly_ sensing fuel octane. This means that running on its normal 87 octane fuel, the 2.0T GDI engine must be running sub-optimal ignition advance and periodically attempting to run more advance while monitoring the knock sensor. Only when a higher octane fuel is used do those advances not result in increased knock sensor activity and allow more power to be made (this may actually require a shut down and restart cycle which can reset the knock multiplier value to a higher starting point from where it would normally learn _down_ to 87 octane).

So, in summary, we know that Hyundai claims more power and a fatter torque curve on 91 octane. This tells us that the 2.0T GDI is running sub-optimal ignition advance on 87 octane. It also tells us that Hyundai is using a bounded ignition strategy with knock learning (which I would be 100% sure of even if they told us nothing). Thermodynamics and engine theory tell us that running sub-optimal timing results in decreased power and efficiency. The conclusion? The engine will produce more power and potentially greater efficiency on higher octane fuel. This dovetails well with the reports from a variety of owners on a variety of forums about their improvements in economy using 91-93 octane. It also is supported indirectly by the results from IL's test of the 1.4 turbo Chevy Cruze on high octane.

Thanks Church, as a 2011 Optima SX 2.0T owner I may just try it out on the next fuel up or 2 (back to back) and see if the ol' butt-dyno notices :) along with the trip ODO

That's really the only way to tell if its worth it, cwescapexlt4x4. If you can't notice 10 hp (and most people can't) and you don't pick up any meaningful fuel economy, then what's the point of spending the extra money? I look forward to hearing about your results.

If it were me, I'd probably run 87 octane in the cool winter months and then run 91 octane when the temps come up since that's when the limitations of 87 octane would be most noticeable.

**sigh**
There are tables that are programmed into the CPU, that the computer follows which determine how the engine reacts to fuel. Timing and detonation are part of those tables, temp, ATM pressures, and sensors look for these values.
Its been stated in the Hyundai forum in the following way:

The car will NOT know the octane, it is simply "written" to see 87, and work within the parameters of the stock tune. It is not "seeking" the octane, nor self-adjusting to the highest timing possible. It is working off all the parameters in the table, and lastly,....once all else is adjusted for, sensing for pre-detonation. If pre-detonation is detected, it retards timing accordingly. The timing is not a runaway train, only braked by the octane.

The program is written in a way, relative by the way to all the other stock parts on the 2.0T, to rarely, if ever allow detonation, even on 87 octane.

This reasoning bolsters the theory that running anything over 87, without re-writing the tune, is indeed useless. The tune rules.
The Inside Line Chevy Cruise issue tested in death valley, not where most drive. It would be the exception, not the rule, as the increased octane reduces predestination under those extremes.

Any hp gains which can be felt by your butt dyno, are all in your head. In dyno tests, yes they claimed to get more hp, but no more torque and they only occurred under higher loads.
So again, without changing the values from the tables the computer follows (reprogramming the computer) tell me again how spending more for a fuel which only retards predetonation under higher temps and pressures, can improve performance without changing boost pressures, compression ratio, etc, and remapping the computer?
What you are basically saying is analogous to adding a bigger power supply to your computer in order to make the cpu run faster. It's not going to happen without other hardware and circuit upgrades. Computers can only do what they are programmed to do. Seems you have the theory and mechanical aspects down, but left out the computer piece. I've been doing both for over 20 years.
Thanks for the exchange, it's been fun!

Frigging auto correct...it's predetonation, not predestination as stated above ;)

Don't sigh at me optimasx. You don't even begin to understand the terminology and the theory you're attempting to spit out onto the page. You've never, ever tuned a car which is quite evident by b.s. you're regurgitating. Oh, and BTW, one of my degrees is a BSEE which I used to land a job designing microprocessors back in the early 90's.

Again:

1) Hyundai themselves state that higher octane fuel will return more power and a fatter torque curve (meaning more torque both below and above the peak torque rpm). This has been stated directly from Hyundai people, on the record in many venues including to Edmund's IL editors.

2) If the car will return more power on higher octane fuel (unless you are calling Hyundai liars then?), it must have a bounded ignition strategy using a knock sensor to optimize timing levels. Otherwise, how else would the ECU know to run more ignition advance, boost, etc.? By your original logic, if the ECU didn't run an active knock advance setup, it would lose power if you put 91 octane into a car tuned for 87 octane due to lower BTUs.

You clearly didn't read or didn't comprehend the nice little intro to ignition timing strategies that I provided you earlier, so just focus on the above two points. Maybe you can press your head against your computer display and absorb through osmosis if that's what it takes. Simply put - if a car returns more power/torque using a higher octane fuel, it must be using an active knock strategy to continually adjust timing looking for the maximum safe advance level. If you think you can argue that point, please feel free to explain to the rest of us how a car with a ECU that doesn't use bounded ignition tables with an active knock strategy will make more power on higher octane without any other changes to the vehicle. But if you do have a way, you might want to file a preliminary patent first....

Did I say butter knife?
Make that a rubber spatula...

Both Church's and optimasx's comments presented a good opportunity for learning. Thank you for that. I may have missed this in the comments, but my question to you all: Does the ECU need to be reset (or battery disconnected) to use different timings/settings when going from 87 to 93 octane? Or will it adjust per the "ignition tables" as it senses a different mixture. Much appreciated!

@optimasx:

/owned.

@optimasx;

/owned

An ECU reset would be the quickest way of learning, but it should learn over time even without a reset.

@optimasx

I understand you're really proud you spent $25k+ and don't want to feel like an idiot, but stop acting the Kia Optima is the perfect car with no flaws, it has MANY! You just don't know what a real car drives like so you don't understand.

You've obviously spent some time on forums because you regurgitate big words like a No Child Left Behind kit taking the SATs.

But the more you type, the dumber you show yourself to be. So just shut up while you're ahead... errrr, before you're too far behind ;)

I work for Hyundai, the Sonata uses the same ECU and turbo setup as the Optima 2.0T. The master tech himself said he wouldn't buy either engine if he knew some stupid owner had been running 87 the whole time.

Stop being a cheap ass (you bought a Kia so I know you already are) and spend the extra $5 a month it's gonna cost you to put in the proper fuel.

cheap bastards lol

I have a 11 Sonata 2T and it does seem to do better on gas with 91. Went to Milwaukee and back clear day 48 degrees and got 36 miles per gal. Have made the trip to the airport many times and with 87 got 33. I know this is not scientific but it does seem to be true, or am I a nutty cheap old
bastard?? I have more miles on the sonata than the test optima and so far no problems. It seems to be a great engine!