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      10-11-2012, 12:09 AM   #1
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My reflection on 87 Octane (vs. 93)

So my brother thought he was being nice by putting gas in my car, but little did he know that I fill it up with 93... Anyway, I noticed some things here, and was just wondering if others in this situation noticed the same. This is regarding my N54 engine, although I assume the same experience would occur with the N55, could be wrong.

First, I am getting much better mileage! I'm just below a half a tank, with the amount of driving i've done, I should be below a quarter tank! This, apparently is the upside, in my personal experience.

However, performance is compromised, as expected. The torque is just plain slower, and I notice much more lag. It is easily noticeable, since I drive always with 93 in the tank.

IMO having the 93 is a must. If there are people out there not running 93 then you're not realizing the most potential of the car.

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      10-11-2012, 12:17 AM   #2
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Kudos to your brother for putting gas in the tank!

I can't even imagine putting regular gas into a turbo motor. The engine controls will keep harm from being done (short term), so you could use it in a pinch.

It does handcuff performance, though.

Even my NA 128 is set up for premium gas. Inside the fuel filler door, it does say "91 octane recommended." I haven't used anything else.
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      10-11-2012, 05:48 AM   #3
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You are getting better mileage because the engine has retarded the timing to compensate for the lower octane. If u really want good gas try sometime mixing a gallon of e85 with regular 87 octane. I used to do this n my turbo a4 and the difference in performance from 91 or 93 was amazing. You have to be careful though because too much e85 will 1 harm your fuel components or 2 make the octane to high and the car will go in limp mode. Basically I would run my tank below a quarter left. Throw n 1 gallon on e85 and then fill up the rest with 87. E85s octane is an average of 106 so when mixed with regular it makes it about 96 or 97 which is like what they have in Europe and Japan and partly why their cars perform better.
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      10-11-2012, 06:12 AM   #4
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If you get better gas mileage at the expense of performance, does that suggest that 87 would be good for a long road trip where power isn't a concern? My fuel door says "minimum 89 octane"... so I can't imagine that I'd be damaging my engine if I used that.

On the other hand, if I'm using the "fuel economy" mode on my JB4 tune, the timing is probably already adjusted without needing to change the fuel grade...
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      10-11-2012, 08:25 AM   #5
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First, I am getting much better mileage!

Simply put, No way!
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      10-11-2012, 09:05 AM   #6
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Quote:
Originally Posted by Walt White Coupe View Post
First, I am getting much better mileage!

Simply put, No way!
Agreed. Lots of misinformation. There is no difference in energy content between different octane grades, so I don't believe there will be differences in mileage.
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      10-11-2012, 11:25 AM   #7
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Agreed. Lots of misinformation. There is no difference in energy content between different octane grades, so I don't believe there will be differences in mileage.
Premium fuel gets better gas milage because the higher octane allows the engine to advance timing because it doesn't see knock as early. This inproves the efficiency of the engine and equates for slightly better gas milage as a result, tho it is not much, maybe 1 mpg if that. Likely the OP is just seeing a random sample that is higher than his average.
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      10-11-2012, 11:44 AM   #8
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Originally Posted by Bmwbreed View Post
You are getting better mileage because the engine has retarded the timing to compensate for the lower octane. If u really want good gas try sometime mixing a gallon of e85 with regular 87 octane. I used to do this n my turbo a4 and the difference in performance from 91 or 93 was amazing. You have to be careful though because too much e85 will 1 harm your fuel components or 2 make the octane to high and the car will go in limp mode. Basically I would run my tank below a quarter left. Throw n 1 gallon on e85 and then fill up the rest with 87. E85s octane is an average of 106 so when mixed with regular it makes it about 96 or 97 which is like what they have in Europe and Japan and partly why their cars perform better.
^Thanks for the info!


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Agreed. Lots of misinformation. There is no difference in energy content between different octane grades, so I don't believe there will be differences in mileage.
^It's not misinformation. I'm not telling you that you'll get better mileage. I'm simply telling you that this is what I experienced. I've been pushing the engine harder, to try to get rid of this gasoline, lol, and it won't disappear like it usually does.
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      10-11-2012, 01:27 PM   #9
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^Thanks for the info!
That info's not 100% correct tho. Retarding the timing across the board makes the engine less efficient. The same amount of fuel is injected, it is just burned at a different, less efficient time. Equaling worse gas mileage.
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      10-11-2012, 03:21 PM   #10
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Quote:
Originally Posted by Stohlen
Quote:
Originally Posted by FIRST1 View Post
^Thanks for the info!
That info's not 100% correct tho. Retarding the timing across the board makes the engine less efficient. The same amount of fuel is injected, it is just burned at a different, less efficient time. Equaling worse gas mileage.
Well I'll be the first to admit when I'm wrong so if I am forgive me. But I thought when the timing was slowed so was the rate at which fuel was burned. To put it simply a more powerful engine needs more fuel and if you aren't operating at 100% power capacity then it may burn a bit longer. Not necessarily more efficent because its not creating as much power as it could. But I've been wrong before so if I am my apologies. It always felt like tho the few times I had no choice but to use crappy gas in my a4 (premium is limited n north dakota this why we mixed e85 at times) it lasted forever. IDK.
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      10-11-2012, 04:17 PM   #11
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Quote:
Originally Posted by FIRST1 View Post
IMO having the 93 is a must. If there are people out there not running 93 then you're not realizing the most potential of the car.
We don't get 93 in California, only 91. Oh, and as of today, it's hovering around $5/gal. But thanks for the suggestion.
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      10-11-2012, 04:42 PM   #12
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Quote:
Originally Posted by Stohlen View Post
That info's not 100% correct tho. Retarding the timing across the board makes the engine less efficient. The same amount of fuel is injected, it is just burned at a different, less efficient time. Equaling worse gas mileage.
I was mostly referring to the suggestion of adding a gallon of E85 into the tank. Although, I've found that there's no conveniently located gas stations near me that offer it, so I probably won't be using E85 anytime soon.

In regards to whether or not better fuel consumption is realized with lower octane, it seems like there's too many variables to fully come to a conclusion. It just seems that from my experience with it, I've made a conscious effort to consume more of this 87 octane, yet I still notice an obvious difference in how much gas I have left. In any case, I'm just surprised that there's no research that's been conducted to come to a conclusion on this (if there is, excuse me, b/c I haven't came across it yet.)
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      10-11-2012, 05:28 PM   #13
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Its a pretty well known fact, theres been load of research over the years. Nothing recent however because it is considered a law of automotive science.

And pushing your car harder on 87 octane to use up gas is a very unwise decision when your car requires premium.
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      10-11-2012, 06:19 PM   #14
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Well I'll be the first to admit when I'm wrong so if I am forgive me. But I thought when the timing was slowed so was the rate at which fuel was burned. To put it simply a more powerful engine needs more fuel and if you aren't operating at 100% power capacity then it may burn a bit longer. Not necessarily more efficent because its not creating as much power as it could. But I've been wrong before so if I am my apologies. It always felt like tho the few times I had no choice but to use crappy gas in my a4 (premium is limited n north dakota this why we mixed e85 at times) it lasted forever. IDK.
Timing isnt slowed, its retarded, which just means the spark happens earlier. The earlier the spark, the further the piston is from top dead center when combustion starts. Which means more pressure builds that the piston must fight as it rises to top dead center, and thus less horsepower per power stroke.

For example: if an engine run with 87 octane makes 100 hp at 50% throttle, firing 10 degrees before top dead center. And that same engine run on 93 octane makes 105 horsepower at 50% throttle, firing 5 degrees before top dead center. Then you could reduce the throttle of the engine when run on 93 octane to 45% and make 100 horsepower and save some gas, while getting the same amount of power as the 87 octane.
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      10-11-2012, 07:57 PM   #15
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Quote:
Originally Posted by Stohlen
Quote:
Originally Posted by Bmwbreed View Post
Well I'll be the first to admit when I'm wrong so if I am forgive me. But I thought when the timing was slowed so was the rate at which fuel was burned. To put it simply a more powerful engine needs more fuel and if you aren't operating at 100% power capacity then it may burn a bit longer. Not necessarily more efficent because its not creating as much power as it could. But I've been wrong before so if I am my apologies. It always felt like tho the few times I had no choice but to use crappy gas in my a4 (premium is limited n north dakota this why we mixed e85 at times) it lasted forever. IDK.
Timing isnt slowed, its retarded, which just means the spark happens earlier. The earlier the spark, the further the piston is from top dead center when combustion starts. Which means more pressure builds that the piston must fight as it rises to top dead center, and thus less horsepower per power stroke.

For example: if an engine run with 87 octane makes 100 hp at 50% throttle, firing 10 degrees before top dead center. And that same engine run on 93 octane makes 105 horsepower at 50% throttle, firing 5 degrees before top dead center. Then you could reduce the throttle of the engine when run on 93 octane to 45% and make 100 horsepower and save some gas, while getting the same amount of power as the 87 octane.

I just learned something new. Thanks man. While I know a decent amount I don't know everything.
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      10-11-2012, 08:22 PM   #16
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Lots of misinformation here... I think Stohlen might be the only person that knows what he's talking about. No offense to anyone, just a warning to not believe everything you see posted on the internet.
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      10-11-2012, 11:01 PM   #17
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Quote:
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And pushing your car harder on 87 octane to use up gas is a very unwise decision when your car requires premium.
Do any of the engines (N51/N52/N54 et al) have knock sensors?

My old E36 with the M42 engine had multiple knock sensors connected to the engine block...

Just wondering.
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      10-12-2012, 12:10 AM   #18
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Interesting information here. Glad I brought this up on the forum. Still not convinced that I'm not getting better gas mileage though!
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      10-12-2012, 03:12 AM   #19
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What does your display read? This discussion doesn't have to be subjective.
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