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      04-20-2017, 01:02 PM   #1
BuffSlut916
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E92 Octane Rating

Hey whats up guys. Normally I put in 91 octane (Chevron) but recently, I've ran a bit short so opted for 87. Is this detrimental to the motor at all?
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      04-20-2017, 01:04 PM   #2
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I'd keep an bottle (or two) of octane booster in your trunk. Just in case you run into this again.
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      04-20-2017, 01:17 PM   #3
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Any brand you'd recommend? I'm looking between VP Racing and Gold Eagle
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      04-20-2017, 01:17 PM   #4
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^ This. Definitely get some booster in.

I'm pretty sure the gas cap says min. rating of 91.

What happens if you put a lower octane than your car requires?

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In short, MAYBE nothing. This one is kind of a big risk. The stack exchange article says that a modern knock sensor will correct for lower octane fuel. This is true, but only in steady state conditions; like cruising down the road, or steady uphill, etc. Transient conditions are where the problems lie. Since it does take time to analyze the knock sensor signal, fast changes in engine load or speed, are difficult to prevent knock. Every automaker is going to be different in this regard, since the ability to analyze this knock quickly depends on the skill of the programmers and calibrators and even the speed of the PCM processor. So, if you put in a lower octane fuel, and then go drive your car hard, press the accelerator quickly, it is possible to experience heavy knock, and possible engine damage. I will say, it is unlikely to actually happen in cars produced in the last few years, but you are certainly exposing your engine to the possibility. ALWAYS, ALWAYS, ALWAYS use the fuel recommended in the owners manual of your car, or any signs on the fuel door or cap. When engineers say to use a certain fuel, we have good reasons for doing so.
http://oppositelock.kinja.com/the-re...ane-1785829176
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      04-20-2017, 01:22 PM   #5
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Do NOT use octane booster in these cars. You will foul the spark plugs and potentially lose performance.
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      04-20-2017, 02:04 PM   #6
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Hm ok. This may be a dumb question, but what is engine knock?

I usually cruise around in my car on the highway and rarely punch it until I get my pockets back up next week.
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      04-20-2017, 02:27 PM   #7
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Quote:
Originally Posted by BuffSlut916 View Post
Hm ok. This may be a dumb question, but what is engine knock?

I usually cruise around in my car on the highway and rarely punch it until I get my pockets back up next week.
Engine knock (otherwise known as dieseling) is premature detonation of the charge in the cylinder. Insufficient octane can cause this as the high compression and high combustion chamber temperatures can ignite the fuel before the intended ignition occurs. This can damage pistons and connecting rods (or more) and can cause valve (and other) damage if valves which are supposed to be shut during the power stroke are open.
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      04-20-2017, 02:33 PM   #8
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Would the best way to mitigate this be driving at low rpms until next week?
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      04-20-2017, 02:35 PM   #9
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Quote:
Originally Posted by m3m3mr View Post
Do NOT use octane booster in these cars. You will foul the spark plugs and potentially lose performance.
If it's a consistent measure then, yes, perhaps. Not half a bottle mixed with half or quarter tank of 87.
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      04-20-2017, 02:36 PM   #10
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Is the tank full? If not, go get as much 93/94 as you can fit in there lol.

Do not use octane booster.

Either way you'll be okay, the engine management is smart enough to adjust timing for 87. Just don't drive it hard.
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      04-20-2017, 02:37 PM   #11
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Originally Posted by BuffSlut916 View Post
Would the best way to mitigate this be driving at low rpms until next week?
The best way would be to syphon out most of the gas in your tank and fill up with premium fuel. Barring that, the risk of damage is lowered by not straining the engine, but I would also recommend topping off the tank every day or 2 with the highest octane gas you can find over the next week or so (depending upon how much you drive) to up the overall octane level of the gas in your tank.
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      04-20-2017, 02:47 PM   #12
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Isn't buying bottles of booster going to cost you more than the difference in buying 91 vs 87 octane fuel?
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Last edited by M43S7RO; 04-20-2017 at 03:07 PM.
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      04-20-2017, 02:48 PM   #13
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Thread of the year nominee.
      04-20-2017, 03:15 PM   #14
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I really don't mean this the way its going to sound but what are you driving an M3 for if you can't afford the gas?
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      04-20-2017, 03:20 PM   #15
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Haha I can I just figured I'd be ok with 2 tanks of 87 for a week. I think 91 is the highest around me. I'm at half right now. I'll fill up some 91 after work, Valero offers a discount with cash
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      04-20-2017, 03:39 PM   #16
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Quote:
Originally Posted by BuffSlut916 View Post
Haha I can I just figured I'd be ok with 2 tanks of 87 for a week. I think 91 is the highest around me. I'm at half right now. I'll fill up some 91 after work, Valero offers a discount with cash
For some reason every time I read your username it registers at "ButtSlut69". Is this intentional?
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      04-20-2017, 03:48 PM   #17
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Quote:
Originally Posted by BuffSlut916 View Post
Hey whats up guys. Normally I put in 91 octane (Chevron) but recently, I've ran a bit short so opted for 87. Is this detrimental to the motor at all?
When you say ran a bitshort, what do you mean?

You cannot afford 91 versus 87? If so, I hate threads like that. You are driving the performance benchmark between the years of 08-13.....if you cannot afford a dollar more per gallon than you should not have the car.

If a bitshort means something else, I retract that statement.
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      04-20-2017, 03:51 PM   #18
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Reading some of the other OP's post, I think the dude is a troll. So you put 87 because you were short on funds? The difference is pennies on the dollar.
"Discounts on gas with cash". Talk about penny pinching
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      04-20-2017, 03:52 PM   #19
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Quote:
Originally Posted by m3m3mr View Post
Do NOT use octane booster in these cars. You will foul the spark plugs and potentially lose performance.
Curious to learn - why is that?
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      04-20-2017, 05:25 PM   #20
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Quote:
Originally Posted by Shredicus View Post
For some reason every time I read your username it registers at "ButtSlut69". Is this intentional?
Lmao not at all
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      04-20-2017, 05:32 PM   #21
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Quote:
Originally Posted by R3dliner View Post
Reading some of the other OP's post, I think the dude is a troll. So you put 87 because you were short on funds? The difference is pennies on the dollar.
"Discounts on gas with cash". Talk about penny pinching
Yeah had to pay over a grand for convertible roof parts, paint, cabin sensors, little shit like that. Diagnostics ran me $200, sensors themselves ran me $400, roof parts $200, paint $200, labor $200 at BMW Mountain View.

But point taken regarding octane rating. The guy at the dealership told me it was chill for a little bit but not to make it a habit.


Out of curiosity, is there a limit for octane ratings for the S65 when filling it with 100+ race gas?
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      04-20-2017, 06:17 PM   #22
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Quote:
Originally Posted by Helmsman View Post
Curious to learn - why is that?

There's a thread somewhere here with guy had fouled up orange colored spark plugs from octane boost. The plugs on our cars serve as knock sensors.
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