89 vs 93 Octane


#1

I have an 08 Dodge Charger 5.7 V8. The manual says I should use 89 Octane. However, the gas station that I always go to has 89 and 93 octane for the same price when using the credit card. I understand the difference between Octane ratings and the reason to not spend more money on higher octane gases when you car does not need it. My question is, if price is not a factor is there any benefit at all to using a higher octane?
Thank you


#2

No. If 93 is required then it’s essential. If it’s not required then it’s a waste of money if you pay more. If you can get it for the same price as 89 then go with the 93. It should get the same mpg.


#3

The owners manual for my 2013 Ford Escape with the 2.0L Ecoboost engine specifies regular. The spec sheet gives a rating of 231 HP with regular and 240 HP with premium. So yes, for my vehicle, there’s a small improvement in HP. I’ve always used regular with no problems.

Generally what I’ve read is there’s no improvement in MPG using premium vs regular if your vehicle only requires regular. Higher octane fuel does not mean more energy content in the fuel. Ethanol however does affect energy content and therefore MPG.

I’m unfamiliar with the specs on your challenger.


#4

It’s possible to gain a little more performance and efficiency.
In some situations (accelerating in high ambient temps) the engine can start to knock a little, even with the recommended octane.
The knock sensor will cause the timing to retard, reducing power and efficiency.
My 2006 Matrix will ping once in awhile when accelerating in 90+F weather.
I figure the knock sensor picks it up and backs of the timing a little.
I’m going to fill up with 89 instead of the recommended 87 the next time we’re in a heat wave to see if there’s any difference.


#5

I’d just use the 89 if thats what the manual calls for. Sometimes if you read the small print on the pump you’ll find that they have a higher percentage of ethanol in the higher grade to boost the octane.


#6

If your engine performs well, there is no improvement in using 93 octane. I doubt that it will hurt anything, though.


#7

Same price? I’d go with the 93, you might get a tiny bit more power and/or mpgs. No harm in using it.


#8

In your car it makes zero difference. The only difference between 89 and 93 octane is its readiness to detonate. 89 detonates too readily for engines with high combustion chamber pressures and they can ping or knock (both conditions of improper ignition), so they need a higher octane rating.


#9

If the engine has a knock sensor it might help a little, allow slightly more advance on the timing. Many engines have knock sensors.

Edit - just checked, it does have a knock sensor, so using 93 will probably help a bit.


#10

A station near me would put midgrade on sale at the same price as regular; I never noticed a difference in mpg or performance but then I never tested the performance in my (non-performance) car- 2008 Toyota Matrix. The skeptic in me always wondered if their mid-grade was getting stale- they must sell 75% regular, 20% premium and 5% midgrade.


#11

The only way it’ll make a difference is if your engine has a tendency to preignite with 87 octane and the knock sensor sends a signal to the ECU which then backs the ignition timing off. If the engine runs fine on 89 octane, higher octane gasoline won’t make any difference.

The “knock sensor” is a piezoelectric device tuned to the specific frequency created by preignition. It reacts to preignition. It isn’t preemptive. The ECU won’t advance the timing until preignition begins, it’ll only back off the timing if preignition begins. The two are not the same.

The bottom line is that of your owner’s manual says your engine can use 89 octane and your engine runs fine, higher octane should not affect mileage. If it does affect mileage, than your engine is adjusting for preignition that should not be there. Its root cause might be carbon deposits, a sparkplug running hot, a cylinder running lean, or something else, but something ain’t quite right.


#12

It’s just shelf-space…Back in the day, 1975, gas stations were forced to install a third tank for the new Unleaded Regular fuel 1975 model cars required…There was 90 octane leaded regular, 100 octane leaded premium and the new 87 octane unleaded regular…The cheapest grade was always the leaded regular. There was massive consumer resistance to buying the more expensive, lower octane, unleaded gasoline. Many buyers of 1975-1980 model cars “converted” them to run on the cheaper leaded regular…The governments response was to remove Leaded Regular from the market, leaving service stations with an extra storage tank and extra pumps on the island…Some put in Diesel fuel…But when the 100 octane leaded premium also was banned, it was replaced with Unleaded Premium, (92 octane) the oil companies dreamed up “Mid-Grade” (89 octane) which was just a 50-50 blend of Regular and Premium. This new grade allowed all the pumps on the island to have a product to sell even though not a single vehicle on the road required or specified this grade of fuel…It took the oil companies and car-makers a long time to create a market for both the mid-grade and premium grades of unleaded fuel which had much better profit margins than the Regular product…


#13

Wow my posts disappear! I agree no reason for it IMO ,a friend of mine used to always run midgrade Amoco on a farm for some reason(what did they call it “Silver”)-Kevin


#14

There could very well be a difference. Just because your car is capable of running on a lower octane fuel does not always mean a higher octane will not reap any benefits. I would definitely try it out and check the mileage over time over the routes trying to drive the same speeds while commuting. I have had cars that have specifically said in the manual, they will run more efficiently with a higher octane fuel. It was never an issue of that with these cars, as the issue was; was it worth it to pay the extra amount if the improvement was so little . Where it costs the same amount for you, try it. What do you have to loose ? I don’t see what the big deal is. Test it out yourself ! There are cars out their that will run on different fuel types without specifically saying so in the manual. There could very well be cars that also show some marginal improvement in performance with a higher octane fuel…
Again, it’s a situation where you are testing a hypothesis and advice is that there " should be no difference" not that there will not be a difference. So indeed, we all know there are variations and your motor could be !


#15

It would make sense to design an engine to take advantage of a knock sensor if it has one.
Rather than set compression and spark timing to avoid pinging under all conditions (didn’t work so well in the '70s & '80s), efficiency can be increased by using more aggressive parameters.
Then, when under conditions that lead to spark knock, (high ambient temps, low speeds, heavy loads, carbon buildup) the knock sensor comes into play.


#16

A knock sensor’s function is to prevent damage from detonation (pinging is a form of detonation, as is spark knock). It makes no sense to be designing an engine to operate under conditions that cause potentially damaging detonation. Remember that the only time a knock sensor will be sending a signal to the ECU is when unwanted detonation is occurring. For the knock sensor to send a signal at all means the engine is doing something it should not be doing.


#17

TSMB. But that’s what engine designers do now. As noted above several Ford engines put out more power with premium, but run fine on regular. The do this by using knock sensors and flexible engine timing control.


#18

Claims of increased performance and / or fuel mileage can seldom be detected under real-world driving conditions by using “high octane” or “premium” gasoline …The difference in Octane (87-92) five octane points, is just not enough to support any meaningful difference. I automatically reject any vehicle that requires premium fuel simply because the benefit is largely imaginary while the expense is not…


#19


#20

With great respect, Texases, I’ve heard people claim that their cars run better on premium, but I’ve yet to see and evidence that systems were intentionally designed to induce preignition and then have the knock sensor send a signal to the ECU to compensate in order to enhance performance. I attribute the anecdotal evidence to cars that aren’t running optimally to begin with combined with placebo effects.

Caddyman, car that require premium do so because they boost combustion pressures artificially or have high combustion ratios. They do perform better, but because of the higher combustion pressures, not because of the premium gasoline.