[bnekic]

Originally Posted by sean10mm

BMW recommends 91 octane. Case mother-f'ing closed.

Thank you. You really must be a dumb person to run anything put premium fuel in a forced induction car.

[RPM90]

Originally Posted by Roki_014

i am running on 91 and honestly i can't notice any difference vs 93, and also it costs the same

91 to 93 is very close and likely very little to no difference.
Many places don't have 91 or 93 but they have 92 around here.
The places that have 93 don't have 91, it goes down to 89 then 87.

What stations in your area sell 91? I haven't seen that rating for a while now. Does it actually cost less than 93?

91 is the "recommended" octane for BMW turbo's so you're good to go.
The engines have been tuned to run near or at their peak on that rating, especially since 91 is the best one can get in some states like California.
There may be some difference between 91 and 93 on a dyno, but in everyday driving most of us likely can't tell.

[RPM90]

Originally Posted by EB_F30

Less octane in the fuel is not going to burn as well...more octane equals more power because the fuel is more potent and it's also burning more air...thus making more power. I highly suggest not running 89 in a turbo car, you can lean the car out causing detention, especially in the high RPM's. It's very bad for the engine.

Higher octane fuel does not contain "more potency", nor does higher octane fuel burn "more air". Also, lower octane doesn't cause an engine to run lean just because of it's lower rating.
There are some threads on this forum that explain this more.
But, do an internet research about octane ratings and how they are derived for a better understanding of what "octane" rating means.

I'll try to keep this info brief, you can easily find out the details with some research.

"Octane' is not something that gives an engine more power, nor can it create more power simply by having a higher octane rating.
It is not about how "potent" a fuel is, so having more or less of it does not translate to it giving more or less power.
Gasoline in general has the same thermal units regardless of octane rating.
*Gasoline formulation can result in more or less thermal energy based on it's composition/formulation. For example, look up what adding ethanol will do to the thermal energy of a gallon of gasoline when it's added.

Octane rating refers to a fuels ability to resist detonation under high pressure and heat. A higher octane fuel allows an engine to be tuned to a higher level before detonation will occur. You can advance timing more in an engine, which can give more power, but you then need to run a higher octane fuel in order to take advantage of the advanced timing.
With greater timing advance a lower octane fuel is more prone to detonation, thus you need a higher octane fuel in order to take advantage of the timing advance.

Turbo/super charging increases combustion chamber pressures. Thus, in order to help keep detonation at bay and extract the engines peak potential, you will need to run higher octane fuel, which is more resistant to detonation under pressure.

Fuel octane is rated differently in different countries, because different countries use different methods by which to test a fuels composition and it's ability to resist detonation.
Research Octane Number/RON and Motor Octane Number/MON use slightly different testing methods by which to come up with the
Octane Number.

In the US we use (MON + RON divided by 2), this gives an octane rating that is an average of both tests.
In Europe for example they use only the RON method, which results in a higher octane number, and that's why Euro octane has a higher octane rating than US octane. It's not because US fuel has lower or less resistance to detonation, it's because the MON test results in a lower octane number.
So when a fuel is tested in the US it is an average or RON+MON, and that results in the lower number.

Example: Octane numbers result from testing: (given for example not exact numbers)
RON = 100
MON = 90
In Europe this fuel will be rated at 100 RON/octane rating.
In the US this fuel will be rated at 100+ 90/2 = 95 RON+MON/2 octane rating.
Same fuel, different octane number, because of different test methods.

Gasoline manufactures mix their gas formulations in order to create different octane rated fuels.

Using a high octane fuel, like US 93, in an engine that is tuned to run at it's peak with 89 octane will NOT give that engine more power. In this case you are wasting your money as that engine can't use and doesn't need the the higher octane fuel. It will run at it's peak with either 89 or 93, so no reason to use 93.

If the engine has been tuned to perform at it's peak using US 93 octane, then using a lower octane, like US 87, may result in that engine not producing it's peak performance as the lower octane fuel will likely detonate under that engines design/tuning parameters.
If you use a lower octane fuel in this type of engine, detonation will likely occur to such a point that the cars computer will need to retard the timing in order to keep detonation in check. Retarding the timing will also result in lower power output and the engine not running at it's peak potential.

You can run lower octane in engines that are tuned for higher octane, but you will not get the best performance or peak power that the engine is capable of.

There is more and detailed info on this, just do some internet searches.
You can learn the difference in testing methods using RON and MON.
In the US, it's claimed that MON is a better test for actual driving as the test engine is run at a higher along with some other factors.

[Elk]

Originally Posted by sean10mm

Case mother-f'ing closed.

Hardly. The issue is vastly more nuanced, and interesting, than you pretend.

[bnekic]

^ No it's not. You have a forced induction car, put premium gas in it (91,92,93)...end of story.

[Roki_014]

Originally Posted by RPM90

91 to 93 is very close and likely very little to no difference.
Many places don't have 91 or 93 but they have 92 around here.
The places that have 93 don't have 91, it goes down to 89 then 87.

What stations in your area sell 91? I haven't seen that rating for a while now. Does it actually cost less than 93?

91 is the "recommended" octane for BMW turbo's so you're good to go.
The engines have been tuned to run near or at their peak on that rating, especially since 91 is the best one can get in some states like California.
There may be some difference between 91 and 93 on a dyno, but in everyday driving most of us likely can't tell.

Mobile gas station by my place sells 91 and 93 and they both cost the same

[Elk]

Originally Posted by bnekic

^ No it's not. You have a forced induction car, put premium gas in it (91,92,93)...end of story.

See above, re-read the manual, do some additional research. It's a fascinating subject. It's also highly amusing how non-engineers regularly claim there is only one answer to a mechanical question.

And again, run whatever you would like in your car - bet it 87 or 110 leaded - or anything in between. No one is forcing your gas pump handle hand.

[bnekic]

^ 87 or 110 leaded?!...please stop providing false statements on this forum that might harm members vehicles.

Speak with any reputable tuning shop or engine builder and ask them what kind of gas should be used in a forced induction engine.

[Kozality]

Originally Posted by RPM90

Octane rating refers to a fuel's ability to resist detonation under high pressure and heat.

I tried to explain this earlier in the thread, but I like your explanation a bit better. =)


Once again. Octane does not mean cleaner burning, nor does it contain more energy. It only affects the properties quoted above.

[sean10mm]

So tell me again why people shouldn't use the fuel that BMW recommends under "Recommended Fuel Quality"?

I love how BMW built the engines, but somehow we're going to out-smart BMW with our fuel selection or something. If they're too stupid to know what kind of gas should go in the car they just built why are you even buying their cars? They're Bayerische Motoren Werke AG... but we should fuel their cars based on what some random twats on the internet think instead of using the fuel they list under "Recommended Fuel Quality"?

[JUSKIDN]

the car will tell the service manage you are putting the cheap stuff in her next time you go in for service

[yepeztroncoso]

Here is something interesting from my 2013 BMW 3 series f30 320i luxury line owners manual. This car comes to the Dominican republic, and i guess other latin american regions. Recommends 95 octane, and 91 octane minimum.

Funny thing is, octane ratings aren't even regulated in my country, since the only oil refinery is owned by the government. There is no law that requires the different brands established here to inform about the octane ratings on the fuels they sell (which all come from the same government owned refinery).

Each brand basically sells 2 types of fuels, a regular and a premium. Some aftermarket tests have been done on these fuels and the results were that the "premium" has an octane rating of about 87, with regular a rating of as low as 83.

So sad...

[IMG][/IMG]

[Michael Schott]

Originally Posted by bnekic

Thank you. You really must be a dumb person to run anything put premium fuel in a forced induction car.

Can you please stop saying this? You are just plain wrong. There are plenty of turbocharged and supercharged cars that work fine on 87 octane. Also, modern cars will not be damaged by gas with too low of an octane as their knock sensors will retard the timing instantaneously. The need for higher octane is generally a function of compression, not induction although I'd guess higher volumes of air and fuel require higher octane gas to make peak HP. It really all depends on a car's engine management system.

[S-Dot]

Originally Posted by yepeztroncoso

Here is something interesting from my 2013 BMW 3 series f30 320i luxury line owners manual. This car comes to the Dominican republic, and i guess other latin american regions. Recommends 95 octane, and 91 octane minimum.

Funny thing is, octane ratings aren't even regulated in my country, since the only oil refinery is owned by the government. There is no law that requires the different brands established here to inform about the octane ratings on the fuels they sell (which all come from the same government owned refinery).

Each brand basically sells 2 types of fuels, a regular and a premium. Some aftermarket tests have been done on these fuels and the results were that the "premium" has an octane rating of about 87, with regular a rating of as low as 83.

So sad...

There are three different ways to measure Octane rating - I'm wondering if that manual is listed in RON, and the one that established your local fuel is only 83 / 87 was measuring MON.

Most of the earth uses RON. North America uses the average of RON and MON, which is AKI. Some places still measure in MON, though that's more common in the aviation industry.

83 MON is roughly 87 AKI, or 91 RON, and that's pretty common for regular grade gas.

87 MON is roughly 91 AKI or 95 RON, which is a premium-ish gas.

Just speculating...

[yepeztroncoso]

Originally Posted by S-Dot

There are three different ways to measure Octane rating - I'm wondering if that manual is listed in RON, and the one that established your local fuel is only 83 / 87 was measuring MON.

Most of the earth uses RON. North America uses the average of RON and MON, which is AKI. Some places still measure in MON, though that's more common in the aviation industry.

83 MON is roughly 87 AKI, or 91 RON, and that's pretty common for regular grade gas.

87 MON is roughly 91 AKI or 95 RON, which is a premium-ish gas.

Just speculating...

That would be very optimistic, since the fuel in my country has a very big reputation of being bad.

The 91/95 rating from the manual doesn't say if its MON/RON/AKI but according to your calculations and owners manual from the USA, maybe its a RON rating as you point out.

The tests that were ran by independent studies also don't specify MON/RON/AKI.

In a worst case scenario for me, those 83/87 tests results in my country would be RON or AKI, doubt it would be MON, which would mean really crappy fuel. Either way, I'm thinking of testing an octane booster called TORCO which is supped to be racing fuel, and see how my engine responds to it. Reviews of the product claim it can raise a US octane rating of 95 to like 100.

[Elk]

Originally Posted by bnekic

^ 87 or 110 leaded?!...please stop providing false statements on this forum that might harm members vehicles.

Oh please, the inherent heavy sarcasm and inherent obvious ridiculousness was insufficient?

You honestly believe unsuspecting readers will read this thread and conclude 110 leaded is precisely what they should seek out and and buy for their family hauler? Just wait until they learn of its limited distribution . . . and the price.

Instead, we hope they will rely on the 2013 manual: "BMW recommends AKI 91" and "BMW recommends AKI 89." Either is fine. They will pick one, based on their predilections, and happily drive off.

NB: Amusingly, in the context of this discussion, the 2012 F30 never even mentions premium fuel, only AKI 89.

On a more serious note, forced induction has been refined in the last 30 years. We no longer have problems with an overly hot intake charge arising from compression, no issues adequately cooling the engine, the impellers, etc., no challenges based in timing inconsistencies, we have improved cylinder head and piston designs, . . . blah, blah, blah.

Forced induction has not invariably required high octane fuel for years. This "rule" died with the mandatory 3,000 mile oil change.

Change your points, rotor and distributor cap lately?

[woderd]

I will be running 87. I might loose a few ponies, but its a 335, I dont think I will miss them.

[RPM90]

Originally Posted by Roki_014

Mobile gas station by my place sells 91 and 93 and they both cost the same

Interesting.

I would use 93 if that's the case.
Free octanes!

[RPM90]

Originally Posted by Kozality

I tried to explain this earlier in the thread, but I like your explanation a bit better. =)


Once again. Octane does not mean cleaner burning, nor does it contain more energy. It only affects the properties quoted above.

Thanks.

Correct, yes.

[RPM90]

Originally Posted by woderd

I will be running 87. I might loose a few ponies, but its a 335, I dont think I will miss them.

Did you read the first post?

[jddssc121]

Originally Posted by EB_F30

Less octane in the fuel is not going to burn as well

that made my day

[Monkeycmonkeydo]

So an honest question here... If a shop specialized in 100 octane how much more performance would I get in my 335? Would I notice the car driving better than say 91?