[1bad335]

Originally Posted by Teemo Panda

The manual suggest 89 octane but this is only as a temporary method until you can find 91++

I mean its your car, you can put lower grade gas all the time if you want to, but you will have to face the music soon.

BMW enthusiasts will not hesitate to use Premium gas, Why? Because they love their cars, like they treat it as their own, mostly like 2nd GF, idk that's just me.

My point is, if you don't treat your GF right, they will eventually break up with you, like with your car, if you don't treat it well not only you are asking for a big bill but you are compromising you and your passengers safety~

Interesting I don't ever remember seeing that 89 was only a temp. solution until 91 or better could be located. Where in the manual does it say that? I think the f30 is a great vehicle but putting in 89 is not going to kill it in anyway since BMW themselves states that 89 is acceptable. In the end we can all choose what grade/octane fuel we want to use but....Really. BTW how is using 89 octane compromising my passengers safety?

[wai2sexy]

Originally Posted by tony20009

Off Topic:
Wow, that's a lot more mpg than I get with my E92. Is that because the 335 uses a significantly different motor or is that the Eco-Pro thing doing it's job?

there are a couple things at play that boost efficiency between the f30 and e92. your 07 e92 uses an n54 engine while the 335 f30 uses the n55. the n55 includes various 'upgrades' that boost efficiency which is why it replaced the n54 across the majority of bmw's lineup.

also the last two gears in the 8 speed in the f30 are overdrive gears which help a lot to increase fuel economy. i've regularly noticed that my 335 will shift into 8th gear starting from 40 mph. eco pro works very hard to keep the rpms below 1.5k under most driving conditions.

getting back on topic, 89 is sufficient for most driving conditions. the only time i would not use 89 is on the track or some type of autocross event.

[rmeir]

put the cheapest gas you can find in it, drive it 100k miles and get back to us if the engine stayed together.

[martyp]

Originally Posted by drob23

You ask for solid advice, but I think unless you speak to an engineer who works on combustion systems or maybe a mechanic who's active these days, everyone is just going to give you whatever black magic theories they have. How can one reasonably discern whether the octane level is truly affecting anything?

LOL! Perfect Answer!

[RoundelM3]

I can only say that if the small difference in fill-up price between 89 and 91/93 octane is that big of a deal, then you probably shouldn't be driving a turbocharged BMW. I use Shell V-Power exclusively, and I'll gladly pay the $2-$4 fill-up difference. I cannot imagine why anyone would quibble about this requirement. The engine is designed to deliver its full power and torque with the higher octane; if you use lower octane, the DME will compensate for the lower knock resistance by changing the ignition and fuel mapping, delivering less power and torque. It's personal preference, but I want everything I paid for, and skimping on fuel won't give me that.

[tony20009]

Originally Posted by roundel335

I can only say that if the small difference in fill-up price between 89 and 91/93 octane is that big of a deal, then you probably shouldn't be driving a turbocharged BMW. I use Shell V-Power exclusively, and I'll gladly pay the $2-$4 fill-up difference. I cannot imagine why anyone would quibble about this requirement. The engine is designed to deliver its full power and torque with the higher octane; if you use lower octane, the DME will compensate for the lower knock resistance by changing the ignition and fuel mapping, delivering less power and torque. It's personal preference, but I want everything I paid for, and skimping on fuel won't give me that.

Read the first post, and several of the others. I could care less about saving a dime or two on gas, but my son asked me a question for which I didn't know the answer; I knew only the dogma. Besides which, he's a college student, and he didn't buy the car.

FWIW, I only put premium in my car, unless there's a circumstance that prevents me from doing so, and so far, there's only been one of those.

[RoundelM3]

Originally Posted by tony20009

Read the first post, and several of the others. I could care less about saving a dime or two on gas, but my son asked me a question for which I didn't know the answer; I knew only the dogma. Besides which, he's a college student, and he didn't buy the car.

FWIW, I only put premium in my car, unless there's a circumstance that prevents me from doing so, and so far, there's only been one of those.

Tony,

Unlike in days of yore, when we didn't have computers to constantly monitor our engines and make dynamic mixture and ignition adjustments, the DME will now compensate for lower octane fuels. I recall building a very high-compression engine setup back in the 1970s where the compression ratio was around 13:1, and I had to use premium fuel plus some modifications to the ignition (back when distributors were still in use) to keep it from "pinging" loudly under load. I could have de-tuned it to use regular, but gas was still way under $1 a gallon back then and it was no big deal, plus I wanted maximum output.

I agree, though, that if you run into a situation where you can't get 91/93, it's ok to use 89, but to also expect a little less power output. If that's all you can get, then you can just live with it or buy a bottle of octane booster at the auto parts store and use that, although that stuff is a bit pricey.

[Elk]

Originally Posted by roundel335

I agree, though, that if you run into a situation where you can't get 91/93, it's ok to use 89, but to also expect a little less power output.

The power reduction from 91 AKI to 89 AKI on a modern FI engine is 2% to 3%, here five horsepower or a little more. This is much less than a butt dyno will detect.

The over the counter octane boosters are both expensive and typically ineffective. There have been a number of magazine articles on these additives, probably some of which are on-line.

[RoundelM3]

Originally Posted by Elk

The power reduction from 91 AKI to 89 AKI on a modern FI engine is 2% to 3%, here five horsepower or a little more. This is much less than a butt dyno will detect.

The over the counter octane boosters are both expensive and typically ineffective. There have been a number of magazine articles on these additives, probably some of which are on-line.

Nonetheless, and especially here in a very hot climate, I prefer to use the available 93 octane. I've grown so used to just pushing the "93" button on the pump that it's second-nature now. I've been fortunate not to have gone anywhere that doesn't have 93 available. It may be difficult to feel, but the hotter temps down this way can also contribute to pre-ignition, especially when the ambient air temp is 100+ degrees.

[Elk]

Of course one should run whatever you prefer, for whatever reason.

93 AKI offers no benefit as the engine is tuned for 91 AKI, but there is absolutely no downside.

My point is simply that one is not going to feel a difference in power between 89 AKI and 91 AKI.

[drob23]

Originally Posted by roundel335

Nonetheless, and especially here in a very hot climate, I prefer to use the available 93 octane. I've grown so used to just pushing the "93" button on the pump that it's second-nature now. I've been fortunate not to have gone anywhere that doesn't have 93 available. It may be difficult to feel, but the hotter temps down this way can also contribute to pre-ignition, especially when the ambient air temp is 100+ degrees.

As someone who sounds like they've worked on engines, what are your opinions of fluctuating the octane level (as the OP suggested but went relatively ignored throughout the thread)?

If you go 93 for a couple tanks, then next tank 89, then half a tank of 91 then back to 89, then full tank of 93...aren't you going to create issues? ECU should be changing timing for each configuration based on the knock sensors...so I'd think it not smart to fluctuate. You're fine with 89, but stick to that. Else, just stay with 91/93.

Of course a limited number of knock events are probably not going to create any major issues...would this be different from an older engine without variable cam phasing? Essentially the engine doesn't have the ability to change timing to allow it to run leaner in a cylinder with a high compression ratio (not sure I said that right lol)? I don't know much about engines so I appreciate the insight.

[Elk]

Originally Posted by drob23

If you go 93 for a couple tanks, then next tank 89, then half a tank of 91 then back to 89, then full tank of 93...aren't you going to create issues? ECU should be changing timing for each configuration . . .

The engine does not care. The ECU reacts instantly to changes in load, throttle, air pressure, manifold pressure, temperature, air charge, etc. It is choosing between fuel maps, timing, etc. continually. A new tank of fuel is trivial.

[drob23]

Originally Posted by Elk

The engine does not care. The ECU reacts instantly to changes in load, throttle, air pressure, manifold pressure, temperature, air charge, etc. It is choosing between fuel maps, timing, etc. continually. A new tank of fuel is trivial.

But none of those have to do with octane. I'd think the only way to deduce a change in octane is through the detection of a knock event. Presumably during wot. Once it assumes you're at 87, then how to tell you've changed it back to 93? So if my first assumption is correct, then you're saying it just assumes 93 at all times and then just dials back timing once it detects a knock event? Wouldn't that be harmful?

[Elk]

Actually, these relate to what you are referring to as knocking, especially temperature and load. The ECU is well aware of the characteristics of the burn at all times and quickly adjusts, long before there is any pre-detonation.

A simple example is going up a steep hill, low RPM, heavy throttle on a hot day and then descending down the other side with light throttle having gotten up to speed. The engine will not misfire on the way up and will quickly adjust to greater efficiency on the way down.

[drob23]

Originally Posted by Elk

Actually, these relate to what you are referring to as knocking, especially temperature and load. The ECU is well aware of the characteristics of the burn at all times and quickly adjusts, long before there is any pre-detonation.

A simple example is going up a steep hill, low RPM, heavy throttle on a hot day and then descending down the other side with light throttle having gotten up to speed. The engine will not misfire on the way up and will quickly adjust to greater efficiency on the way down.

I'll admit I don't know much about combustion control systems and I only really follow your example in the context of changing driving conditions. Doesn't the difference in octane correspond to the resistance to detonation as a function of pressure/heat? So unless you actually have pre-detonation or knock, how do the characteristics of the burn change? Especially in a way that can be measured via indirect methods like exhaust manifold pressure or comparing with tables parametrized by load, temperature, intake manifold pressure etc.?

Edit - appears that I'm vastly oversimplifying things and pre-ignition is a lot more common then I'm proposing. Elk is right that things are characterized much more frequently than I proposed, and octane is only a player in the grand scheme. I'll leave my previous comments just for completeness sake. Interesting document that I'll have to read in greater detail - https://static.cobbtuning.com/cobbtu...20FAQ%20v2.pdf

[RoundelM3]

Drob - you are on the right track, but even though our engines have many ways to prevent or reduce pre-ignition, there's always a price to pay in terms of reduced performance, however slight. The engineers who design the engines and their control systems are pretty smart guys, and if they say we should use premium (read higher-octane) fuel for best performance and engine life, then that's advice that should be followed.

It's like the argument that comes up every so often about using E85 (85% ethanol, 15% gasoline) to boost octane and increase power for cars with performance-modified engine software (higher boost, aggressive ignition, etc.). It's great for that, but a steady diet of ethanol will corrode our non-flex-fuel systems, and it's only about 70% the thermal efficiency of gasoline, meaning you get way less fuel mileage. Can you try a tank every so often? Sure, but a steady diet will eventually cause problems.

[Elk]

Originally Posted by drob23

. . . octane is only a player in the grand scheme.

It is truly fascinating stuff.

I'm glad you found a reference that made things more clear than I was doing.

[Mav12]

Today's mass market engines are meant to be used in most of the world, where more often than not 91+ octane is not even available.... If BMW says minimum 89, 89+ is fine. The engine adapts (knock sensors etc as already mentioned). 91+ may give a slight edge to performance and smooth running but I really don't think there is any risk of actual damage.

I would take most people's feelings while driving with a grain of salt... I don't think most of our butts, hands and feet are so sensitive that we can adjust for the host of other factors that day to day (or even hour to hour) would have a much bigger effect on performance (weight, humidity, elevation and the list goes on).

So if it's damage u fear, I wouldn't worry about using a mid grade fuel. Especially if u know u are keeping the car for a handful of years only. But with that said I still use a premium grade when available for my cars, especially because one of them I'm never going to sell! :-)... Any tiny advantage over the LIFE of a car, might actually add up. So for strictly piece of mind and longevity, and also because I don't do a ton of miles, so the cost is manageable, I go premium. I sleep at night better .

[NISFAN]

We are talking about a Turbo charged engine with a relatively high compression ratio.

Anyone who knows anything about turbo charged engines will know that the most important factor in it's design is Fuel Octane. There are charts of boost pressure vs. Octane vs. Compression ratio, in the Turbo chargers bible. If BMW have designed the engine for x octane, it is foolish to run it on lower octane.

Yes the engine has knock sensors, but it also has a map that optimises engine performance which it tries to run to by default unless told otherwise by things like the knock sensors. Running into knock is not good for an engine, even if only temporarily, and using low octane fuel makes this a common occurrence. Knock if severe enough can destroy a turbo charged engine in a matter of seconds: FACT!

Now I can't comment on the engine in question, and how much safety margin it has, but it is turbo charged, and does have a high compression. I would strictly heed the manufacturers advice on fuel octane usage.

Being thrifty is fine, but there are limits. For example you might decide that Bridgestone tyres are 'non thrifty' and fit Nang Jin Fuk's for half the price, or top up oil with 30SAE mineral. These options might seem thrifty to some, but those in the know think otherwise. Where do you draw the line?

[Elk]

Originally Posted by NISFAN

We are talking about a Turbo charged engine with a relatively high compression ratio.
. . .
If BMW have designed the engine for x octane, it is foolish to run it on lower octane.

Yes, and the engine is designed for 89 AKI and up.

By the way, there are forced induction engines which happily run on 87 AKI and up such as the Hyundai Genesis 2.0L turbo. Forced induction does not mean higher octane is required.

[tony20009]

Thanks to everyone who responded to the request I made. I appreciate your sharing the outcome of your personal observations.

Originally Posted by drob23

...

You ask for solid advice, ...

Actually I didn't. I asked for folks to share observations and/or anecdotes of what one may have experienced from having violated the premium fuel mandate. Precious few folks responded with what I asked for. You'll see my original post below.

Originally Posted by tony20009

...

So, if anyone here has tried using mid-grade all the time, have you observed any ill affects from having done so?

I've read a variety of stuff on the Internet about this matter, (http://usatoday30.usatoday.com/money...emiumgas_x.htm among others), but I'm interested in what real owners here are experiencing (not what they think, surmise or believe) from having done so.

[noro]

That's great! Total dollars saved a month: $3.56

How about cancelling that gym membership he never uses.


Joking aside, I don't know you or your son, but I find it a bit "silly" when somebody invests into a car this expensive and then proceeds to turn into a cheapo when it comes to gas.

Originally Posted by tony20009

I bought my kid a 328 F30. He called me this a.m. asking if he really had to put premium gas in it. I told him if he wanted to save some money, he could fill up with premium one time and then going forward, upon the needle showing half full, top it off again with mid-grade octane fuel. I said further that that so long as he keep refueling at the half full point, he could alternate back and forth and be okay, but that if he falls below half, he should only refill with premium.

He doesn't want to do that. (This shouldn't surprise you or me; kids always just want to do it their way, even when they ask and you tell them something other than what they had in mind.) He just wants to use mid-grade all the time.

So, if anyone here has tried using mid-grade all the time, have you observed any ill affects from having done so?

I've read a variety of stuff on the Internet about this matter, (http://usatoday30.usatoday.com/money...emiumgas_x.htm among others), but I'm interested in what real owners here are experiencing (not what they think, surmise or believe) from having done so.