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[ascii42]

I googled the Volvo and it said it has a 8.5:1 compression ratio. Why would you need to run 98 octane in a low compression engine like that?

That's a turbo motor, right? That's probably why.

 

[AstroLad]

87 is just a bit more affordable and since most people don't care about nitpicking their car's performance, this tends to be the norm specially since you consider the compression ratio of the average car as well as every cars in the road.

89 is just a step up to help semi-old cars put less strain in the engine, since it contains higher combustibility putting less strain on the engines, but a bit less "efficient" than 91 (performance wise)

91 is actually far better than most people paint it out to be. Not only is it easier to ignite, but it also contains nitrogen as well as other chemicals that actually do help maintain the cylinders cleaner, and you can even use this grade to help gain higher horse power on older cars by "modding" the spark plugs.

I personally use 91 across all my cars, from the '93 ciera, to the '09 bmw (except the benz which actually required 100-102)

Now if you factor in summer blend vs. winter blend (at least here in socal) the only fluctuation is about 1 to 2 grades (give or take).

Helpful, thanks!

 

[Patrick S.]

I googled the Volvo and it said it has a 8.5:1 compression ratio. Why would you need to run 98 octane in a low compression engine like that?

I'm no engineer

The gas cap sticker and owner's manual both state that the right fuel for my car is 98 RON. The normally aspirated V/S 40's do use 95 RON, though.

 

[Patrick S.]

That's a turbo motor, right? That's probably why.

Yes, it's a turbo.

 

[Septimus Prime]

87 is just a bit more affordable and since most people don't care about nitpicking their car's performance, this tends to be the norm specially since you consider the compression ratio of the average car as well as every cars in the road.

89 is just a step up to help semi-old cars put less strain in the engine, since it contains higher combustibility putting less strain on the engines, but a bit less "efficient" than 91 (performance wise)

91 is actually far better than most people paint it out to be. Not only is it easier to ignite, but it also contains nitrogen as well as other chemicals that actually do help maintain the cylinders cleaner, and you can even use this grade to help gain higher horse power on older cars by "modding" the spark plugs.

I personally use 91 across all my cars, from the '93 ciera, to the '09 bmw (except the benz which actually required 100-102)

Now if you factor in summer blend vs. winter blend (at least here in socal) the only fluctuation is about 1 to 2 grades (give or take).

Actually it's the reverse. Higher octane gasoline is harder to ignite. That's why it's generally required (or at least recommended) in higher compression engines. It can be subjected to higher pressures without premature detonation.

Yeah. You actually get decreased performance/efficiency for using the wrong fuel either way. The uncombusted high-octane fuel just gets wasted.

 

[Baka Sempai]

Actually it's the reverse. Higher octane gasoline is harder to ignite. That's why it's generally required (or at least recommended) in higher compression engines. It can be subjected to higher pressures without premature detonation.

.... ah, ok,. now im lost haha.

I have always assumed the higher the grade, the more "refined" and pure the gas is, thus making it more easily combustible, since the lower one is less pure and some of the contained chemicals were harder to ignite (hence why race pros have to use gas/ethanol mix)

Like for example, my benz has a compression ratio of 11.2:1, when i used 91 octane, i was getting 347 hp, but then with additives and what not i brought it up to 98 octane, which resulted in nearly 420 hp and was told the compression was good, but the fuel was "weak" so i drove to a local track, bought some actual 101 octane, re-ran the numbers and i ended up with a very solid 428hp.

But again, if im wrong, im wrong haha.

 

[Septimus Prime]

.... ah, ok,. now im lost haha.

I have always assumed the higher the grade, the more "refined" and pure the gas is, thus making it more easily combustible, since the lower one is less pure and some of the contained chemicals were harder to ignite (hence why race pros have to use gas/ethanol mix)

Like for example, my benz has a compression ratio of 11.2:1, when i used 91 octane, i was getting 347 hp, but then with additives and what not i brought it up to 98 octane, which resulted in nearly 420 hp and was told the compression was good, but the fuel was "weak" so i drove to a local track, bought some actual 101 octane, re-ran the numbers and i ended up with a very solid 428hp.

But again, if im wrong, im wrong haha.

The fuel being harder to ignite is what's increasing your performance, since it allows your piston to compress the air-fuel mixture more before combustion.

 

[Baka Sempai]

The fuel being harder to ignite is what's increasing your performance, since it allows your piston to compress the air-fuel mixture more before combustion.

But the purity of the fuel allows it to burn at a higher and more stable temperature thus providing better performance correct ?
Meaning than in a higher compression engine, a high octane gas will help more no ?

 

[Septimus Prime]

But the purity of the fuel allows it to burn at a higher and more stable temperature thus providing better performance correct ?
Meaning than in a higher compression engine, a high octane gas will help more no ?

I'm not really sure how octane rating affects purity, but what it does do is that, the higher the rating, the more compression it allows the air-fuel mix before it ignites. With lower octane (high cetane) rated gas, what could happen in higher compression engines is that the heat and pressure from the compression is so high that it ignites the fuel before the spark plug fires, which does all sorts of bad things, like throwing off timing, and not allowing your piston to get a full stroke, which causes knocking and decreased performance.

 

[DoomGyver]

Also octane starts to degrade as soon as it has been refined. So that premium fuel you bought at the gas station might have been in that tank for months if you purchase you fuel from a station that doesn't get a lot of business.

 

[UFO]

But the purity of the fuel allows it to burn at a higher and more stable temperature thus providing better performance correct ?
Meaning than in a higher compression engine, a high octane gas will help more no ?

Octane has nothing to do with purity. It's just a measure of how much compression the gas can take before it auto-ignites. Using low octane gas in a high compression engine would cause it to knock because the gas would ignite before it was supposed to. Modern engine have knock sensors and can adjust timing if it detects this, but at the cost of reduced power.

There are of course better quality fuels, but that doesn't have anything to do with octane.

 

[Baka Sempai]

I'm not really sure how octane rating affects purity, but what it does do is that, the higher the rating, the more compression it allows the air-fuel mix before it ignites. With lower octane (high cetane) rated gas, what could happen in higher compression engines is that the heat and pressure from the compression is so high that it ignites the fuel before the spark plug fires, which does all sorts of bad things, like throwing off timing, and not allowing your piston to get a full stroke, which causes knocking and decreased performance.

Octane has nothing to do with purity. It's just a measure of how much compression the gas can take before it auto-ignites. Using low octane gas in a high compression engine would cause it to knock because the gas would ignite before it was supposed to. Modern engine have knock sensors and can adjust timing if it detects this, but at the cost of reduced power.

There are of course better quality fuels, but that doesn't have anything to do with octane.

Well, i just learned something new today, Thank You
(and i used to consider myself a car enthusiast haha, pfffff..... not even close)

 

[Al-ibn Kermit]

Why do you use such low octane fuel over in the states? The least you can get hear is 95 (Sweden).

Which as explained by some smarter people than myself in this thread is equal to our highest 91 octane due to different measuring scales. I use 91 (your 95) in my my Volvo S40 with the turbo engine but a higher compression ratio requires engine parts to either be more durable or for the consumer to accept that they'll break down sooner. You're simply putting more pressure on everything

For driving in the US where we generally travel a lot more miles per year than you all in Euroland, it might make sense for the manufacturers to design engines to be as low-stress as possible so they can easily last a long time. That's my theory at least.

 

[MasterMongoose]

The other thing people don't get taught often is that higher octane = lower energy density.

So for x amount of gasoline, the lower octane will actually help you travel further (if your engine is calibrated for it). People who needlessly put higher octane in cars are just handicapping their gas mileage.

The other neat thing is that E85 is equivalent to something like 110 Octane, which is why it is a favorite of people with highly modified turbocharged engines (this also points to why E85 cars have such TERRIBLE range compared to their regular ol' gasoline cousins).


I wish all of my cars ran on 87... so much cheaper.

Also people will use 89 in mountainous roads or something, I'm told. I've never looked into it.

 

[ascii42]

Also people will use 89 in mountainous roads or something, I'm told. I've never looked into it.

Yeah, atmospheric pressure, and therefore elevation, has an effect on combustion timing. So lower level octane fuels are available in mountainous regions. Like I think regular is 85 instead of 87, and premium is 89. Not sure if it matters as much on fuel injected cars as it did on carbureted cars.

 

[UFO]

Which as explained by some smarter people than myself in this thread is equal to our highest 91 octane due to different measuring scales. I use 91 (your 95) in my my Volvo S40 with the turbo engine but a higher compression ratio requires engine parts to either be more durable or for the consumer to accept that they'll break down sooner. You're simply putting more pressure on everything

For driving in the US where we generally travel a lot more miles per year than you all in Euroland, it might make sense for the manufacturers to design engines to be as low-stress as possible so they can easily last a long time. That's my theory at least.

American cars have also historically used higher displacement/ lower compression engines then their European and Japanese counterparts. A turbocharger in anything other then a sports car was unheard of here until about 5 years ago.

 

[Iorv3th]

Leaded, Unleaded, Diesel.

Leaded doesn't exist anymore.

Unleaded - Premium - Diesel.

 

[ahoyhoy]

That smells like regular OP.

She needs premium!

 

[DJ Lushious]

My car is 14 years old and some guy at a car shop i go to said that it would increase my gas mileage for some reason and actually be cheaper

Not sure why though

When in doubt, consult the manual.

 

[Baka Sempai]

Also octane starts to degrade as soon as it has been refined. So that premium fuel you bought at the gas station might have been in that tank for months if you purchase you fuel from a station that doesn't get a lot of business.

Wut ?

As others have pointed out, the octane grade is the rate at which the gas combusts, not ignites, hence why the european difference between the american (RON vs. Octane), since over there is rated by its RON if that makes sense.

So for example, if you store 91 Octane in a car for a few years, without being exposed to extreme temperatures or contaminating conditions, you will NOT loose any grade.

It may evaporate if the gas cap is not properly set, but its combustibility properties should remain the same.

After all, Octane is the sum of the RON and the engine's graded performance (MON)
so unless your car loses power from storing gas, and the gas gets contaminated, your octane will remain at whatever grade you put it at (Octane = RON + MON \ 2 )

 

[dodgeme]

They don't even offer 89 Octane in my area, it's ether 87,91 or 93. I exclusively run 93 Octane in my WRX but it is also tuned for that so I try to avoid anything lower.

 

[Box of Kittens]

Every once in a while I'll be at a station that offers several extra grades. A few months back I was at one that had 88. I really had to wonder who uses 88.

 

[Al-ibn Kermit]

American cars have also historically used higher displacement/ lower compression engines then their European and Japanese counterparts. A turbocharger in anything other then a sports car was unheard of here until about 5 years ago.

Yeah. Ford Crown Victoria's 4.6L V8 makes around the same horsepower as the 2 liter in the Focus ST but the reason cab companies liked the crown vic was that it could easily go 500,000 miles with just regular maintenance.

 

[frankie_baby]

I'm not a driver but didn't even know there were different types of petrol, most filling stations I see here in the UK sell either unleaded or diesel and that's it

 

[Septimus Prime]

Every once in a while I'll be at a station that offers several extra grades. A few months back I was at one that had 88. I really had to wonder who uses 88.

Chinese people probably would. 8 is lucky, so more 8s, more better.

 

[Kelsdesu]

If I start getting knock I use 91.

 

[GoldenEye 007]

In Orlando I've seen stations with 5 types of gas from 87 to 91. Can anyone from Orlando explain that?

Yeah I've noticed that sometimes. Also places with race fuel, but those are generally near race tracks. Maybe the additional grades are for certain tools or boats? IDK? There must be some market demand for it for them to stock it.

Edit: I've also seen a few that offer E85 or ethanol-free. Same octanes of course, though.

 

[turtle553]

In Orlando I've seen stations with 5 types of gas from 87 to 91. Can anyone from Orlando explain that?

Some stations might have have 87,89,91 with ethanol and 87,91 without. Common in Virginia at least.

 

[ascii42]

Yeah I've noticed that sometimes. Also places with race fuel, but those are generally near race tracks. Maybe the additional grades are for certain tools or boats? IDK? There must be some market demand for it for them to stock it.

Edit: I've also seen a few that offer E85 or ethanol-free. Same octanes of course, though.

Don't really need to stock more than the highest and lowest grades. They can just mix them to get the grades in the middle.

 

[Stinkles]

I put it in my Honda Ruckus.

 

[GoldenEye 007]

Don't really need to stock more than the highest and lowest grades. They can just mix them to get the grades in the middle.

Ha, yeah that would make sense from a product standpoint. But then still why have it as an option at all, you know?

 

[iamblades]

Wut ?

As others have pointed out, the octane grade is the rate at which the gas combusts, not ignites, hence why the european difference between the american (RON vs. Octane), since over there is rated by its RON if that makes sense.

So for example, if you store 91 Octane in a car for a few years, without being exposed to extreme temperatures or contaminating conditions, you will NOT loose any grade.

It may evaporate if the gas cap is not properly set, but its combustibility properties should remain the same.

After all, Octane is the sum of the RON and the engine's graded performance (MON)
so unless your car loses power from storing gas, and the gas gets contaminated, your octane will remain at whatever grade you put it at (Octane = RON + MON \ 2 )

This is not accurate at all.

Gasoline is not a chemically stable mixture even largely in the absence of contaminants, and doesn't really last for more than a year or so in the best conditions. If you store gasoline in a car for a couple years, I'd be shocked if it even started, much less if it retained the same properties.

 

[Flo_Evans]

Fun fact, there is no such thing. It's just a mix of high and low octane.

 

[KillGore]

GAF, I have a car that's supposed to use premium gasoline but most of the time I just put regular gasoline. Is the car already dead?

 

[ascii42]

Ha, yeah that would make sense from a product standpoint. But then still why have it as an option at all, you know?

Doesn't cost much to offer and enough people buy it for whatever reason to justify the costs, I suppose.

 

[GoldenEye 007]

GAF, I have a car that's supposed to use premium gasoline but most of the time I just put regular gasoline. Is the car already dead?

Probably just reduced performance. Car would be dead eventually if you put in E85 Ethanol, though.

 

[ascii42]

GAF, I have a car that's supposed to use premium gasoline but most of the time I just put regular gasoline. Is the car already dead?

Most modern cars can adjust, which is why they'll "recommend" instead of "require" premium. You'll just get worse performance and fuel economy, most likely. If it can't adjust, yeah, you are damaging your engine.

 

[rrs]

American cars have also historically used higher displacement/ lower compression engines then their European and Japanese counterparts. A turbocharger in anything other then a sports car was unheard of here until about 5 years ago.

Gas is (was?) cheap, so you can get away with increasing displacement for more power and leave the other cool things for higher end models. Today though, the USA divisions are like "hey euro fam can I borrow your engines"

 

[nephilimdj]

Use to use 91 in my Mitsubishi/GM Holden's, ran perfect but then again there muscle cars. Now need 95 in my Alfa Romeo.

 

[Baka Sempai]

This is not accurate at all.

Gasoline is not a chemically stable mixture even largely in the absence of contaminants, and doesn't really last for more than a year or so in the best conditions. If you store gasoline in a car for a couple years, I'd be shocked if it even started, much less if it retained the same properties.

I thought a bottle of stabil and the gas would be fine for at least a year or so, since i based all my info on gas empirical laws (ideal temp, absolute temp, xylene, etc... )
anyways, ....
I'll watch myself out of this thread, i've been nothing but a "wreck" :/

 

[Septimus Prime]

Most modern cars can adjust, which is why they'll "recommend" instead of "require" premium. You'll just get worse performance and fuel economy, most likely. If it can't adjust, yeah, you are damaging your engine.

This is good to know because I think I accidentally put 87 in my X3 a few days ago.

 

[iamblades]

I thought a bottle of stabil and the gas would be fine for at least a year or so, since i based all my info on gas empirical laws (ideal temp, absolute temp, etc... )
anyways, ....
I'll watch myself out of this thread, i've been nothing but a "wreck" :/

If you used a fuel stabilizer(and the tank is full and properly sealed), a year or so sounds about right, maybe up to 18 months.

That doesn't mean the fuel isn't degrading though, it's just slowing the rate down a bit.

There is no way I know of for storing gasoline for two or more years though. Even storing it in a vacuum sealed container doesn't stop the various components of the gasoline from reacting with each other. Eventually a large enough percentage of the molecules will react with various other molecules to render the fuel unusable for it's original intended purpose.

 

[Patrick S.]

Interesting Fifth Gear video where they test what exactly happens if you put the wrong fuel in a car.

 

[TimeLike]

Fun fact, there is no such thing. It's just a mix of high and low octane.

Ha so true. Everything in between is just a blend/grade ratio. Three octane levels to choose? Only two tanks in the ground.

 

[Flo_Evans]

Ha so true. Everything in between is just a blend/grade ratio. Three octane levels to choose? Only two tanks in the ground.

Also a fun fact, you get a bit of whatever grade the guy in front of you pumped that is still in the hose.

 

[Patrick S.]

If you used a fuel stabilizer(and the tank is full and properly sealed), a year or so sounds about right, maybe up to 18 months.

That doesn't mean the fuel isn't degrading though, it's just slowing the rate down a bit.

There is no way I know of for storing gasoline for two or more years though. Even storing it in a vacuum sealed container doesn't stop the various components of the gasoline from reacting with each other. Eventually a large enough percentage of the molecules will react with various other molecules to render the fuel unusable for it's original intended purpose.

I've seen videos of people starting up barn finds that had not been started for years. The biggest problem of leaving fuel in a car for a long time is that the fuel will erode the rubber/plastic hoses it has contact with and the resulting dirt in the fuel line will clog or glue shut your injectors.

 

[TimeLike]

Also a fun fact, you get a bit of whatever grade the guy in front of you pumped that is still in the hose.

If they're out of low grade, buy the middle grade because it'll be 100% high grade!

 

[Patrick S.]

Also a fun fact, you get a bit of whatever grade the guy in front of you pumped that is still in the hose.

In Europe we have one hose per fuel type.

 

[mmazurkiewicz]

I drove a new 535i today that required 89 or 91. I'm on the east coast and we only get 87, 89, and 93 so I used 89.

It felt weird as I only ever have to use 87 or 93 around here depending on the car.

 

[UFO]

I've seen videos of people starting up barn finds that had not been started for years. The biggest problem of leaving fuel in a car for a long time is that the fuel will erode the rubber/plastic hoses it has contact with and the resulting dirt in the fuel line will clog or glue shut your injectors.

They probably put fresh fuel in it though.