93 octane single pump nozzle

[nOLd]

Are you really getting 100% 93 octane in a Gas Station that has a single pump nozzle? Is it possible your getting some 87 or 89 mix?

Thanks

[murellus]

If the person that pumped gas before you at the same pump filled up with a different grade you will certainly get at least a little of that gas. However, the amount in question is so small that the effects of it on a whole tank of gas is beyond negligible, unless you were filling a quarter gallon for some stupid reason.

[nOLd]

Originally Posted by murellus

If the person that pumped gas before you at the same pump filled up with a different grade you will certainly get at least a little of that gas. However, the amount in question is so small that the effects of it on a whole tank of gas is beyond negligible, unless you were filling a quarter gallon for some stupid reason.

mannn is so hard to find a gas station that has 3 nozzles, most of them only has 1 .

Thanks,

[SunnyD]

You guys are lucky you get 93 octane out there...we only get 91 in CA

[nOLd]

Originally Posted by SunnyD

You guys are lucky you get 93 octane out there...we only get 91 in CA

I think its the same 91 and 93 Octane

[Hawkeye]

Originally Posted by nOLd

I think its the same 91 and 93 Octane

It isn't. Pretty much all we have in Iowa are the 3 nozzle ones.

We are kind of a weird state though... we have E85 readily available, 89 is cheaper than 87 (the cheapest actually), and depending on which station you go to you can get 91, 92 or 93 octane for high grade.

Plus, unless you have modified your ECU I believe the Zeds are naturally calibrated for 91 octane so it is slightly less efficient if you use the higher octanes.... that is mostly hearsay from another thread though.

[Kamal]

Here in St. Louis its pretty much 87/89/91 or 87/89/93... personally, I only use 93 octane Shell V-Power.

[OH FO SHO]

Originally Posted by SunnyD

You guys are lucky you get 93 octane out there...we only get 91 in CA

imagine how much more 93 would cost ...

at some 76 gas stations in so cal you can get get 100-110 octane at the pump

[pbdm4k]

On my Z, I used to run 94 octane all the time, but with the rising gas prices I've gone to using 91 octane.

As odd as it is, I'm finding that I am indeed getting better mileage from 91 octane.

[mazzawi]

I'm putting 94 octane,
but I was thinking about the octane stuff,
what i understand is octane rating, means restance to knocking, which is kind of a miss fire in the cylinder because of the high pressure igniting the fuel prematurely?
since these engines are not turbo's, the pressure in the cylinders is not as high as a turbo car,
so there is probably no need to pay for higher octane, especially if your not at full throttle, there will be even less pressure in the cylinders.

[Stoky]

Originally Posted by mazzawi

I'm putting 94 octane,
but I was thinking about the octane stuff,
what i understand is octane rating, means restance to knocking, which is kind of a miss fire in the cylinder because of the high pressure igniting the fuel prematurely?
since these engines are not turbo's, the pressure in the cylinders is not as high as a turbo car,
so there is probably no need to pay for higher octane, especially if your not at full throttle, there will be even less pressure in the cylinders.

My understanding of it is that engines have certain compression ratios, and designed for a certain octane. WIth BMW though, the engine is design to run at 93 octane, however there is a computer that will regulate the firing to prevent knocking etc if you use a lower grade. SO this means the car will not knock however there is a chance you may loose a little preformance and possibly gas mileage since the cylinder is not optimally moving. This means you may save 10cents at the pump per gallon but say you loose .25 miles per gallon you probably break even. So it really doesn't matter. Now if gas was at the price it was 3-5 years ago then you would probably save $.

This is my general knowledge from the web, i am sure someone knows more about this stuff and might give a better answer.

[cardebt]

Maybe it was an anomaly, but at one point I put 93 octane in my F150 and it ran like sh!^. Once I was through the tank it returned to normal. I know the cars have sensors to control knock, but this was bad.

[Hawkeye]

Originally Posted by OH FO SHO

imagine how much more 93 would cost ...

at some 76 gas stations in so cal you can get get 100-110 octane at the pump

In Iowa 91,92 and 93 all cost the same.

[The HACK]

Sigh...Where do I begin?

First, turbo or force induction engines actually have much lower cylinder compression ratio than typical BMW NA engines. For example, the N54 runs a 10.5 : 1 compression ratio where as the N52 runs a 11 : 1 compression ratio, and the S54 is as high as 12 : 1. The main difference is the air entering into the cylinder in an FI engine is already compressed. The compression ratio simply means the cylinder will compress the air down to that ratio before the spark ignites the air/fuel mixture.

The problem with gasoline, is that it's highly flammable. Compressing the gasoline/air mixture sometimes leads to premature detonation of the mixture before the ideal compression ratio is reached and before the spark goes off, especially in high compression cars. The act of compression actually heats up the mixture, so what they do is put in RETARDANTS in the fuel to prevent it from igniting prematurely. So actually, higher octane fuel burns slower.

I know what you're going to ask next. Why do we put "higher" performance gas in the engine when it actually BURNS SLOWER? Simple. If the fuel ignites prior to the pistons reaching the top of its travel, what happens is the gas is expanding while the piston is moving upwards, creating massive stress on the cylinder walls and leading to premature failure. Ideally, you want the fuel to burn when the spark goes off, which is typically right at or after the apex of the piston travel. Fuel igniting prior to the spark is what's called "detonation" or "ping" in the engine.

In a modern BMW high compression engine or any FI engine, it is typically designed to run on high octane fuel not because it burns faster, but it burns SLOWER. So how exactly does that improve performance? Well, the amount of energy released in a gallon of gas is the same regardless of how fast it burns. If you can increase the compression ratio, that means you get more air in the system per liter of displacement and the engine combustion is more efficient and if you can control the rate of combustion you can increase performance and efficiency by running higher octane (slower burning) fuel.

So, in short, you should run fuel with the octane rating your engine is designed to run. For example, if you have an engine with a very low compression ratio, like 8.5 : 1 (say, a typical truck engine designed for low-revving, low-end pulling torque), it'll probably run best on 87 or 89 octane gas because the low compression does not create a detonation problem. Putting in higher octane gas would actually make the car run worse, because the slower burn nature of higher octane gas. You would actually get a lot of unburnt gas existing the exhaust port fouling up the O2 sensor. However, on a high compression engine designed to run on high octane gas, running low octane gas would result in pinging or detonation leading to premature engine wear.

What BMW has done to get around the masses who do not comprehend the nature of gasoline octane properties, is to put a "knock" sensor in the engine to detect ping or detonation due to low octane gas, and retard engine spark (by making the spark fire later in a combustion cycle) to alleviate the problem. The result is lowered fuel efficiency and reduced performance, but the general masses probably won't feel the difference.

How's that for a freakin' long winded post?

[Hawkeye]

^^^ Freakin' awesome! I did not know that. Thanks!

[rc'Z]

Good job Hack. I'm able to run regular in one of my cars in the winter, but in the summer, regular knocks, so I move up a grade. Same driving habits, difference in temperature.

[nOLd]

excellent

[The HACK]

Originally Posted by rc'Z

Good job Hack. I'm able to run regular in one of my cars in the winter, but in the summer, regular knocks, so I move up a grade. Same driving habits, difference in temperature.

I have a beef with that logic and here's why. If you're running 89 octane gas on a car that's designed to run 91 or better, but has a knock sensor to retard timing, how much are you actually saving? In most areas 89 is about 10-12 cents cheaper than 91, that leads to about $1.50-$2.00 per fill-up. Extrapolate that to an entire year's worth of fill-up, say 12,000 miles (and let's just pick a conservative number, like 22 mpg), That's about $800 in savings out of $2,500 in gasoline. Well, at this point you're probably saying, $800 is a month and a half of payment on my car, it's not insignificant. And you would be right.

But what most people are not factoring in is by running 89 octane on an engine design to run 91 you are losing fuel efficiency. Let's pick another moderate number, say, 89 octane is about 5% less efficient than 91, so instead of 22mpg you get 21mpg instead. And let's say, 91 octane cost $4.50/g compared to $4.40/g on 89. Again, extrapolate that out, you actually get $2,454 per year filling up with 91 octane and $2,514 per year filling up with 89 octane, it actually cost you MORE to fill up with the cheaper gas (go figure).

In reality, if fuel cost is a real concern, and say, you average 70 mph on your 30 mile a day commute, you will save a lot more by averaging 5 mph slower on that commute than to use cheaper, lower octane gas. You would easily see 2-3 mpg improvement and that will dramatically impact your bottom line. And by averaging 5 mph slower you may also minimize the impact on fuel efficiency and engine wear when running with a lower octane gas because you're placing a much lower load on the engine.

I've gotten past having to be the fastest driver on the freeway (in my 20s you'll often see me blasting down the freeway at least 10-15mph faster than the fastest car on the road), now I just strive to be the fastest car on the track.

[Stoky]

Originally Posted by The HACK

But what most people are not factoring in is by running 89 octane on an engine design to run 91 you are losing fuel efficiency. Let's pick another moderate number, say, 89 octane is about 5% less efficient than 91, so instead of 22mpg you get 21mpg instead.

In reality, if fuel cost is a real concern, and say, you average 70 mph on your 30 mile a day commute, you will save a lot more by averaging 5 mph slower on that commute than to use cheaper, lower octane gas.

I know that you are more knowledgeable on this area than me and agree that you should use the octane the car was made for. However, here in chicago to get 93 octane it is 20-24 cents more per gallon, which is what is recommended. So useing the price for 91 octane might not be totally fair. Also I completely agree that preformance drops with lower octane, but how can you be sure its 5%. I have never seen any data for that. However, I agree in the end I would think you at best break even in terms of price over the long haul in using the lower octane.

In terms of speed I can remember watching a History channel special about cars/gas mileage and they said in general cars run optimally at 70mph in terms of gas mileage, which is why some states raised the speed limit to 70 maybe 10-15 years ago. Now going above 70 you see a reduction and driving at 60 you get a little less value. It really is the hard/fast accellerations that kill you on the mileage.

Not trying to refute your facts, because you obviously know more about this than me. So these two statements are more of questions that rebutal.

[Yal]

i've done tests where I averaged my fuel consumption over three tanks driving always in the fast lane, then the same always in the slow lane. Fast lane speeds were typically 65-70 mph and i'd get around 22 mpg. This is +/- .5 mpg. Do the same where i'm running 50 to 55 in the slow lane and i'm up at 25 with about the same +/- .5. This is a 12 mile drive on the freeway with the cruise on. Some uphill, some downhill.

My background is engineering test and analysis for both mechanical and semiconductor process engineers. I've done thousands of tests and analysis of results over the last 25 years, so when i set out to do these impromptu, non-scientific tests, I keep things as regulated as possible. Same gas, same station, even same fill up time. Also, I run it to almost the same fuel level in the tank. I currently fill at about 8 gallons down. And yes, my life is incredibly repetetive and possibly boring, but this is the kind of thing I do for fun.

Is slowing down ruining the fun factor? Don't know about that, I drive for fun on the weekends or days off, not when i'm headed to work.

[wasupdu]

I do A LOT of freeway trips since my gf lives out of state so I think I get very good mileage in my vehicles (all require premium fuel).

2005 Z4 - 27 mpg
2005 525i - 26.5 mpg
2007 Yamaha R1 34 mpg

Sure I could buy a hybrid but those aren't as fun to drive ......unless I had a Tesla of course.

[The HACK]

But to answer the original poster's question, yes you can be sure that you're getting 93 octane gas even with a single nozzle. All the gas station ever really store, are the highest octane they carry and the lowest in 2 separate tanks, and they mix the in between grades by mixing the two gas. 50% 91 octane and 50% 87 octane to get 89 octane. So when you're pumping premium, it only draws fuel from the premium tank.

At least that's the way I understood it and it's been explained to me this way.