Premium vs Regular Gas

[brfatal]

If an engine is designed to primarily operate on premium fuel (91+ octane), then you will see a degradation in performance and economy. 87 and 89 octane fuels burn faster (and can cause pinging or knocking). The engine has knock sensors and can adjust the timing and injectors to compensate for the lower octane fuel. This in turn, causes lower HP output and a decrease in economy. On the other hand, a car designed to operate on 87 octane will not see ANY improvement or performance improvement by using 89 or 91 or 93 octane fuel.

Having said, that, there is NO advantage to fiddlefarting around with the 'stock' timing as the CPU does that anyways on the FLY as needed. This isn't your dad's muscle car.

The problem is that your knock sensors will only tell the ECU to pull timing AFTER it knocks. There are no such thing as predictive sensors. While all cars do knock, it's always considering a bad thing. Your ECU will pull timing when you're running lower octane and then slowly start to advance it. If you're still running lower octane it will detect knock again and retard the timing and advance, retard and advance in an endless cycle. In the long run I'd expect this affect the health of your engine, particularly your ringlands.

 

[mikec]

Modern knock sensors are very sensitive and engineers mount them to specific points on the engine block that vibrate the most due to knock. (technically mounted to "nodes" instead of "anti-nodes" where engine mounts are ideally located) So even slight knock, which doesn't hurt the engine much at all, can be picked up by the knock sensor and in turn the ECU. Remember "pinging" - the rattle sound older engines made during hard acceleration? That's a type of knock - a "light knock" really. Today's knock sensors can detect vibrations about 1/10th to 1/100th those magnitudes.

Also, the oxygen sensor feedback can have a step change in output when knock occurs, helping the ECU predict impending knock/pinging.

mike c.

 

[HughH]

The 1991 Audi 100 (5000) was the very first car that "I" saw with anti-knock sensors. Since then, just about every car sold in this country is equipped as such.

I just noticed a couple of days ago, the No.1 gas station (Mobil) by revenue in this city stopped carrying medium and high octane gas. They only carry low octane and diesel.

BTW - Automakers are required to certify the gas milage of their vehicles every year. That information goes on the sticker of the new car. Also, EPA must must make a record, specifying the octane used for those tests. It does NOT mean the the auto will/will not run with any other octane gas. What it means is that they cannot advertise horsepower and milage using a different octane than the one tested. Doing so would violate all kinds of Federal regulatios. So, when the automaker recommends or requires a type of octane, it means that's the octane required for the auto to achieve the test and advertised performance.

I have used low octane on many of my cars such as a 2004 (now sold) BMW330i, especially after my SA confessed that the dealer used low octane on all of their cars.

So, use whatever you feel like using. In my case, I don't track any of my cars anymore. That's when I always used the highest octane available. For driving around the city/suburbs, I have yet to find a car that I could detect a change in performance. If I did, then I would have to weigh the amount of improvement vs. the difference in $$$ at the pump and my type of driving.

BTW - In my travels through some third world countries, I noticed high octane is only available in some major cities. German cars such as BMW, Audi, MB, are very popular and therefore, must be able to run on low octane without any damage to their expensive engines.

When I was stationed in Iceland back in the 70's, the only gas available in the whole county was low octane, highly sulfuric. It was imported from Russia and sold by Texaco on base. I had to have the timing reset in my SAAB in order to be able to run the car without inflicting any damage to it's engine. No fuel injection yet...

 

[QuantumRift]

The knock sensors are very very sensitive and detect sound and shock vibrations well before a human could figure out the engine is knocking. When the engine starts to knock, the sensor picks it off well BEFORE any engine 'damage' is done. The CPU and engine are designed to all work in harmony....O2 sensor, knock sensors, air flow meters, temperature sensors, air pressure sensors, all work with CPU so that the CPU can orchestrate the optimal fuel and engine settings for economy. That's what the mfg programs into the CPU. Can you bypass it? Sure, you can, but there's always a cost.

Engines that are flex fuel ALSO determine what kind of fuel is being delivered to the injectors so the engine can adjust the timing and injectors to utilize the, for example, E85 fuel. They do not determine the type or blend of fuel by chemical analysis. I know that on Fords, a sensor is installed the high pressure fuel line in the engine compartment. It measures the fuel conductivity, temperature and its dielectric constant (the ratio of the amount of electrical energy stored in an insulator) to determine the alcohol content in the fuel. The flex fuel sensor then sends a duty cycle "command" to the CPU to tell it what it the fuel it is sensing. The frequency of that signal increases as the alcohol content increases.

The problem is that your knock sensors will only tell the ECU to pull timing AFTER it knocks. There are no such thing as predictive sensors. While all cars do knock, it's always considering a bad thing. Your ECU will pull timing when you're running lower octane and then slowly start to advance it. If you're still running lower octane it will detect knock again and retard the timing and advance, retard and advance in an endless cycle. In the long run I'd expect this affect the health of your engine, particularly your ringlands.

 

[QuantumRift]

Yes, when you increase the compression ratio you MUST use a higher octane fuel to keep the compressed air-fuel mixture from spontaneously exploding (knocking).

10K miles on the clock. Been running regular the whole time. Hit 27 MPG on long trips. More than enough power to get me into trouble. I don't really see a reason to run premium at this time. Maybe if I was racing or something. But this is supposed to be the family car.

However I will say this, I run premium in my Harley. But that is because I built and tuned the engine to run on premium. It dosen't like regular. I also ran premium in my hotrod truck for the same reasons, it just wouldn't run on regular. Maybe the blower sitting on top had something to do with that.

 

[brfatal]

The knock sensors are very very sensitive and detect sound and shock vibrations well before a human could figure out the engine is knocking. When the engine starts to knock, the sensor picks it off well BEFORE any engine 'damage' is done. The CPU and engine are designed to all work in harmony....O2 sensor, knock sensors, air flow meters, temperature sensors, air pressure sensors, all work with CPU so that the CPU can orchestrate the optimal fuel and engine settings for economy. That's what the mfg programs into the CPU. Can you bypass it? Sure, you can, but there's always a cost.

I'm sorry but this is false. If it were true then there would be no blown motors in the performance tuning world. Knock sensors only detects knock AFTER it happens, so that means that it will only pull timing after the damage (depending on how bad the knock conditions are) is done. My point is that if a car is has a "recommended" fuel grade, then that should be the grade used. Is that word of law? No, but over the long haul there could be an issue.

 

[InTheLou]

Hyundai OEM Specs:
3.8 Liter 4.6 Liter
Regular fuel*: 290 hp @ 6200 RPM 378 @ 6500 RPM
Premium fuel*: 290 hp @ 6200 RPM 385 @ 6500 RPM (+7HP)
Torque (lb-ft @ rpm):
Regular fuel*: 264 @ 4500 324 @ 3500
Premium fuel*: 264 @ 4500 333 @ 3500 (+9 lb-ft)

Source: 2011 Genesis 30 Page Buyers Brochure page 28
Page 12 "An Extraordinary 385-HP V8" ....and here a nice bonus: It can safely run on both premium and regular fuel while still delivering a rush of adrenaline when you plant your right foot."

*octane ratings of fuel not listed

I know the R-Spec will give more horsepower, but the 4.6, has less than 2% boost of horsepower and would not likely be noticed if you did not know what was in your tank. Think of it as adding the power of a weak riding lawn mower, not a Sears 20 hp. If the car is running hot (your temp gauge), then you may have a problem, but I doubt you will see a difference with fuel. The 3.8 and 4.6 did not have a lot of difference in performance specs in 2011, though I think the 4.6 is a better engine. The higher the horsepower goes, the rear end, transmission, clutch (it would be nice to have a manual R-Spec), braking, cooling system should all be upgraded. I think we see some of that with the R-Spec (tranny), but a lot is cosmetic (badges, wheels, tires, etc.) and who is the car really targeted towards? I believe Hyundai found a customer that they were not targeting as much before, those looking for a very high performance luxury sedan, hence the jump in HP, the R-Spec, and more performance to come in 2014 (let's hope the cost doesn't rise as much also). Would be nice to know sales totals of the 6-8 and R-Spec over the last year?

0-60 times, not any difference with the fuel, remember, you do have several hundred extra pounds of weight with the larger engine, transmission, etc. This is not the model of car to start removing the spare, taking out the A/C (or not running it), to start lowering weight to gain a 1/4 second at 0-60, or your 1/4 mile time. Maybe someone is really doing mods and running the track (maybe they have some good specs to share), but you don't see this very often with every day drivers in this category of large sedans.

 

[Aquineas]

There is another potential consideration if you have a 2012 or later. Gasoline Direct Injection, or GDI. I've been doing a ton of reading on this in the last couple of days, as this is my first GDI vehicle.

There are a lot of articles out on this, but here is one that sums up the potential issues nicely. Basically a potential problem with GDI is the buildup of oil residue on the intake valves. In a port-injection engine, those deposits get washed away by the incoming fuel (since the fuel is injected upstream of the intake valve). In a GDI engine, the fuel is injected directly into the cylinder, bypassing the valves entirely, thus allowing (over time), the buildup of carbon on the intake valves.

In any case, this particular statement from the link above is most curious, and might be relevant in the discussion of Premium vs. Regular:

The reason these issues have slipped through to production is that they won’t show up in a 500,000 mile torture test. These types of issues will appear after years of short trips (preventing the engine from reaching operating temperature), bad batches of fuel, etc.

I couldn't find in that article (or any other article I've read) any specific info on the correlation on bad fuel and its potential impact on the engine, so I can only surmise that the lower the fuel quality, the greater potential for carbon buildup on the intake valves.

Now before someone jumps in and says "higher octane isn't necessarily higher quality", I do understand that. I am going under the assumption that with a higher octane fuel, the ignition point of the fuel is more closely controllable, and thus the downstream systems such as EGR etc can do their jobs better.

I'm not an engineer (well, not a mechanical one), so take all this as wild speculation on my part.

Here are some other interesting articles on GDI:
http://www.autoobserver.com/2011/06/direct-injection-fouls-some-early-adopters.html
http://www.thetruthaboutcars.com/2009/11/hyundai-the-new-honda-in-engine-design-leadership/

 

[Potty_Pants]

There is another potential consideration if you have a 2012 or later. Gasoline Direct Injection, or GDI. I've been doing a ton of reading on this in the last couple of days, as this is my first GDI vehicle.

There are a lot of articles out on this, but here is one that sums up the potential issues nicely. Basically a potential problem with GDI is the buildup of oil residue on the intake valves. In a port-injection engine, those deposits get washed away by the incoming fuel (since the fuel is injected upstream of the intake valve). In a GDI engine, the fuel is injected directly into the cylinder, bypassing the valves entirely, thus allowing (over time), the buildup of carbon on the intake valves.

Comming from BMW that was plagued with the carbon build up (i'd post pictures but im too lazy, just search for 335i carbon build up) basically in 50K miles the cars ran like crap and they had to be walnut blasted (about $800). once completed Idle,gas mileage and performance returned.

there are some manufacturers tweaking the DI to reduce carbon build up or possibly eliminate it.

carbon build up & hyundai was a thread i was thinking about posting... though i fear it would go unanswered... so never did.

ppp

 

[bobshine]

I doubt if anyone on this board is as cheap as I am, but has anyone noticed that if you fill half your tank with 87, and half with 93 that you get a 90 octane tank for the price of a 89 octane? Just a thought. I use 87, but if I needed to go up a level, I'd do the 1/2 87 and 1/2 93 to get 90 for the price of 89.
Most of the time I can tell how many gallons I will need to fill up even before
I start to pump.

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[TimeOut]

I doubt if anyone on this board is as cheap as I am, but has anyone noticed that if you fill half your tank with 87, and half with 93 that you get a 90 octane tank for the price of a 89 octane? Just a thought. I use 87, but if I needed to go up a level, I'd do the 1/2 87 and 1/2 93 to get 90 for the price of 89.
Most of the time I can tell how many gallons I will need to fill up even before
I start to pump.

Gas stations only get two grades. 87 and 93. The pump mixes both of them to create 89 and 91 grades. Here in Houston we don't get 91 for some reason.

Back in the summer of 2008 when Premium was $4.50+ a gallon here in Houston and I had to fill up my BMW, I started making 91 myself by doing a mix of 50% of 89 plus 50% of 93 because 91 is the lowest grade you can put on BMWs according to the manual.

 

[Crusty Old Shellback]

DId you actually test the octane of your mixed gas to show that your speculation of mixing 1/2 87 and 1/2 93 would result in 91?

I think it's a little more involved than just mixing the two gases at a 50/50 blend.

 

[brfatal]

Gas stations only get two grades. 87 and 93. The pump mixes both of them to create 89 and 91 grades. Here in Houston we don't get 91 for some reason.

Most of the country does not get 91. 91 does not come from mixed batches as you mentioned.

 

[TimeOut]

DId you actually test the octane of your mixed gas to show that your speculation of mixing 1/2 87 and 1/2 93 would result in 91?

I think it's a little more involved than just mixing the two gases at a 50/50 blend.

It is called blending. Back in the '90s, I used to work for a company (overseas) that sold and installed Gilbarco's fuel dispenser around that country.
The most popular dispenser we sold was the model that allowed the gas stations to blend regular and premium grades to create one mid range grade. From the top of my head, to create the 91 octane grade you need to blend 51% of 93 with 49% of 89.
Of course, if you are at the pump doing this blending manually, you are never going to accomplish a perfect 51/49 blend.

 

[QuantumRift]

Sir, I was NOT speaking of the "performance tuning world". I taking about off-the-LOT rides. I stand by my statement, which is NOT false. It it fairly OBVIOUS that the recommended fuel SHOULD be used, however, I would NOT run lower octane fuel in an engine designed for HIGHER octane fuel unless there were mitigating circmstances. My old '90 Isuzu pickup, 2.6L EFI engine is designed for 89 octane fuel. However, it spent the last 22 years in Sierra Vista, AZ where the altitude is 4600', so MOST of the year, I ran REGULAR fuel in it. I also drove it to the TOP of Pike's Peak in Colorado several times (14,100' in elvation) on 85 octane fuel with no issues at all. None. The Smart For 2 car recommends PREMIUM fuel in the manual. Can you operate it on midrange or regular fuel? YES. Why? The PRESIDENT of Smart For 2, Dave Schembri went on the record as specifically stating you could, but that "performance and mileage would suffer". It will NOT destroy the engine or harm the engine as the engine is SMART enough to compensate for it. Knock sensors detect it while it IS happening and the CPU nearly instantaneously adjusts the engine parameters to compensate. Your statement is "overblown". When I did put lower grade fuel into my truck, the engine did not BLOW or detonate or destroy itself or toss pistons out the side of the block. I had a gentle "pinging" sound - NO KNOCK, that told me I should put a bottle of octane booster into the tank and switch to mid grade fuel until cooler weather came. As the proper fuel gets used out of the lines and the lower octane fuel starts being used by the injectors, the CPU already knows with even the faintest change in combustion to make adjustments. It's a tried and true method and the sensors are very very sensitive to changes in the process, and any abnormality is picked up and sent to the CPU. Simple.

http://www.camberleyautofactors.com/home/products/37-engine-management/274-emc-knock-sensors

http://wiki.answers.com/Q/What_does_a_knock_sensor_do

I'm sorry but this is false. If it were true then there would be no blown motors in the performance tuning world. Knock sensors only detects knock AFTER it happens, so that means that it will only pull timing after the damage (depending on how bad the knock conditions are) is done. My point is that if a car is has a "recommended" fuel grade, then that should be the grade used. Is that word of law? No, but over the long haul there could be an issue.

 

[Crusty Old Shellback]

It is called blending. Back in the '90s, I used to work for a company (overseas) that sold and installed Gilbarco's fuel dispenser around that country.
The most popular dispenser we sold was the model that allowed the gas stations to blend regular and premium grades to create one mid range grade. From the top of my head, to create the 91 octane grade you need to blend 51% of 93 with 49% of 89.
Of course, if you are at the pump doing this blending manually, you are never going to accomplish a perfect 51/49 blend.

I understand blending. They do it with oil as well to get the different viscosities of oil.

But just trying to get people to understand that you can't mix 50 % of 80 with 50% of 90 and expect to get 85. It just dosen't work like that.

As for fuel, I've run regular in my '04 chevy truck, 5.3L for 80K miles now with no issues. I also ran it in my Pontiac G8 for 40K miles with no issues. I'm running it in the Genney R Spec as well. I see no need to spend .25 a gallon more for Premimum just to gain a few extra ponies to drive the family around. She has more than enough power now to get me into trouble.

 

[brfatal]

Sir, I was NOT speaking of the "performance tuning world". I taking about off-the-LOT rides. I stand by my statement, which is NOT false. It it fairly OBVIOUS that the recommended fuel SHOULD be used, however, I would NOT run lower octane fuel in an engine designed for HIGHER octane fuel unless there were mitigating circmstances. My old '90 Isuzu pickup, 2.6L EFI engine is designed for 89 octane fuel. However, it spent the last 22 years in Sierra Vista, AZ where the altitude is 4600', so MOST of the year, I ran REGULAR fuel in it. I also drove it to the TOP of Pike's Peak in Colorado several times (14,100' in elvation) on 85 octane fuel with no issues at all. None. The Smart For 2 car recommends PREMIUM fuel in the manual. Can you operate it on midrange or regular fuel? YES. Why? The PRESIDENT of Smart For 2, Dave Schembri went on the record as specifically stating you could, but that "performance and mileage would suffer". It will NOT destroy the engine or harm the engine as the engine is SMART enough to compensate for it. Knock sensors detect it while it IS happening and the CPU nearly instantaneously adjusts the engine parameters to compensate. Your statement is "overblown". When I did put lower grade fuel into my truck, the engine did not BLOW or detonate or destroy itself or toss pistons out the side of the block. I had a gentle "pinging" sound - NO KNOCK, that told me I should put a bottle of octane booster into the tank and switch to mid grade fuel until cooler weather came. As the proper fuel gets used out of the lines and the lower octane fuel starts being used by the injectors, the CPU already knows with even the faintest change in combustion to make adjustments. It's a tried and true method and the sensors are very very sensitive to changes in the process, and any abnormality is picked up and sent to the CPU. Simple.

http://www.camberleyautofactors.com/home/products/37-engine-management/274-emc-knock-sensors

http://wiki.answers.com/Q/What_does_a_knock_sensor_do

I used performance tuning as an example. There are cars that come from the factory with at-risk motors that blow unmodified. '07 and up WRX/STis for example have had issues on and off with finicky ECU parameters that have very little tolerance for variance. Detonation is what's killing these motors, and if the knock sensor worked as you said then this would simply not be the case. Unfortunately for a few hundred people it is. Again it's a damage done system. It will only pull timing after knock has already occurred. And if you're using lower octane gas continuously when the ECU tries to advance it will knock again. Rinse and repeat. These may only be minor bumps, but over the life the car it's not a stretch to say that this can add up.

 

[scottdk]

Also an interesting read for those who have not seen this.....

http://www.genesisowners.com/hyundai-genesis-forum/showthread.php?t=5401