[davis449]

Originally Posted by david in germany

What is "premium" in this case? Premium is not an octane rating it is an octane range. The industrial standard is 91 and up is premium.

In this case we're talking about 91 Octane. Auto manufacturers making cars for the US know what grades of gasoline are widely available to the lowest common denominator in the country. For the vast majority, that lowest octane "premium fuel" is 91.

As mentioned before, in my 335i when I am running my aggressive tune I must run the higher 95 octane (98 here in Germany)

Yes, I already covered that specific circumstance in my previous post.

When I say run the lowest octane your car can take I am referring to the lowest octane the manufacturer recommend (look inside your filler door)

And when I said it wasn't entirely true, I meant go back and read what I wrote concerning cars that can and do perform better on premium which is why they print "premium fuel recommended for maximum performance" inside the gas tank filler as well as in the owners manual. Therefore, running the lowest octane that car can take will not yield maximum performance.

[F32Fleet]

A few years ago I read about some experiments with no spark direct injection gas engines. Yes, as is no spark like a diesel. I suspect they were using a very low octane fuel.

[david in germany]

Originally Posted by davis449

In this case we're talking about 91 Octane. Auto manufacturers making cars for the US know what grades of gasoline are widely available to the lowest common denominator in the country. For the vast majority, that lowest octane "premium fuel" is 91.


Yes, I already covered that specific circumstance in my previous post.


And when I said it wasn't entirely true, I meant go back and read what I wrote concerning cars that can and do perform better on premium which is why they print "premium fuel recommended for maximum performance" inside the gas tank filler as well as in the owners manual. Therefore, running the lowest octane that car can take will not yield maximum performance.

I still don't think you got my point. 91 octane is the base premium standard. Yes a car recommend to use premium fuel will run better with 91 octane than it would with 89 octane fuel. But most of the time that same car will still see no advantage with running 93 or 95 octane over the 91. Each car is different though so there are exceptions. And as I mentioned before, in my two cars I found a decreased performance and a mpg decrease when I used 95 instead of 91 octane.
This was tested and tracked with road trip app on my previous commute (50 miles one way autobahn) cruse control set to the same speed every day and traffic conditions always similar barring special conditions.

People still should follow the manufacturers recommended octane and typically will see no increase in power or efficiency with running higher than recommended.

[Red Bread]

Originally Posted by F32Fleet

A few years ago I read about some experiments with no spark direct injection gas engines. Yes, as is no spark like a diesel. I suspect they were using a very low octane fuel.

HCCI. It hasn't really been proven to work, but rumor says Mazda is close. Sounds like a blended fuel, primarily gasoline with a mix of diesel is the best way to bring down the knock risk.

[Zippster]

Originally Posted by david in germany

You should do a bit of research on it. Higher octane does not equal more power. Higher octane does allow for more aggressive timing in the engine. The lower octane is less stable than higher octane. you should run the lowest octane your vehicle can take for the most power and efficiency.

Higher octane allows for more compression which equals more power.

[davis449]

Originally Posted by david in germany

I still don't think you got my point. 91 octane is the base premium standard. Yes a car recommend to use premium fuel will run better with 91 octane than it would with 89 octane fuel. But most of the time that same car will still see no advantage with running 93 or 95 octane over the 91. Each car is different though so there are exceptions. And as I mentioned before, in my two cars I found a decreased performance and a mpg decrease when I used 95 instead of 91 octane.
This was tested and tracked with road trip app on my previous commute (50 miles one way autobahn) cruse control set to the same speed every day and traffic conditions always similar barring special conditions.

People still should follow the manufacturers recommended octane and typically will see no increase in power or efficiency with running higher than recommended.

I see, I see. I thought I had implied this already. I do apologize.

[Fundguy1]

Originally Posted by JsL

Meanwhile in CA... the Air Resource Board looks to ban 91 and 89, as cars that require those fuel are higher performing and less economical. Also a 200% new car tax on anything not a Hybrid or Plug-In.

Move, or better yet take his or her office.

[eluded]

No

[davis449]

Originally Posted by Zippster

Higher octane allows for more compression which equals more power.

Not unless the car is tuned for it.

[Zippster]

Originally Posted by davis449

Not unless the car is tuned for it.

I think you missed my point, I'm talking about if higher octane fuel becomes available, manufactures will be able to design engines with a higher compression ratio, which they will obviously tune for. Not a current design and just adding more boost.

[DKX4///M]

It seems noone here actually knows what octane even means...93 (aki ) is "average knock index" it's Europe's rating scale RON which stands for something like raw octane number and other countries use MON... Aki is RON+MON / 2....Octane in simple terms is like one user said it's stability. The higher the octane the harder it is to burn...it says nothing about the potential energy of the fuel. For example ethanol has almost half the pe of gasoline which is why it strains fuel pumps....if a boosted cars VE, says it required a BRAKE specific horsepower of .7 gal/hr per bhp of gasoline it will require upwards of n1 gal /hr per bhp of ethanol or methanol....a race fuel (non alcohol) will have more or the same stored energy as 93 octane but as resistant to knock as e100.

That being said higher octane does allow for more timing especially higher revs, and more dynamic compression or actual cylinder PSI at TDC. However more timing does equal more power to a point, then it will begin to fall off...also some tuners put limits on boost and timing no matter the octane. Some engines with lower compression and no boost won't pull timing with 89...in these cases using a higher octane than required to achieve 0 knock sensor activity and no timing pull or boost drop, using harder to burn fuel will lower power and mpg...

The N55 has anot unusually high static compression ratio of 10.5 to 1 and runs huge boost....Usually this means very high (hot) cylinder pressure... it also seems and this is an educated guess it has a high stroke to bore ratio as engines that produce massive torque often do. High stroke engines can relieve some of that pressure by opening the exhaust valve early on the exhaust stroke which 1. Gives a more complete evacuation of the cylinder allowing for more fresh air/fuel on the intake stroke. 2 it lowers parasitic draw (it's much easier to move a piston up in a cylinder with valves open) 3. With VANOS and the engines ability to almost infinity co3ntrol both lift and duration of both intake and exhaust valves giving the engine more precise control over actual combustion chamber pressure,,,

It can even open the exhaust valve at the end of the combustion stroke being almost all the power is being generated in the earlier stages of combustionn stroke again especially in a high cr long stroke engine...

IN CLOSING in our M2, run the highest octane possible, even boosters (depending on the ingredients which is a whole not her story) but unless u want to destroy your fuel pump twice as fast avoid anything more than e20, e30...I'd say it's befits at those levels are more due to water attraction ando lowering Temps than actual octane, unless your pumping it in through a separate alcohol friendly fuel pump like port injection.

We all know the M2 Produces 30 more whp, with high octane. Ms100, 93+ @ good reputable Oct booster or alcohol through a friendly pump. If the car doesn't require 93 u r throwing money away

Sorry for the long post just trying to inform everyone of very basic but very important info

[david in germany]

Originally Posted by DKM3Power

It seems noone here actually knows what octane even means...93 (aki ) is "average knock index" it's Europe's rating scale RON which stands for something like raw octane number and other countries use MON... Aki is RON+MON / 2....Octane in simple terms is like one user said it's stability. The higher the octane the harder it is to burn...it says nothing about the potential energy of the fuel. For example ethanol has almost half the pe of gasoline which is why it strains fuel pumps....if a boosted cars VE, says it required a BRAKE specific horsepower of .7 gal/hr per bhp of gasoline it will require upwards of n1 gal /hr per bhp of ethanol or methanol....a race fuel (non alcohol) will have more or the same stored energy as 93 octane but as resistant to knock as e100.

Exactly. Certain engines can take advantage of the higher fuels by advancing the timiming (based on the tune) If knock occurs and the engine can retard. I really don't know of any car that can read the octane level and adjust for it. Most cars can sense knock and adjust for it though.

[DKX4///M]

Originally Posted by david in germany

Exactly. Certain engines can take advantage of the higher fuels by advancing the timiming (based on the tune) If knock occurs and the engine can retard. I really don't know of any car that can read the octane level and adjust for it. Most cars can sense knock and adjust for it though.

I'm not 100% certain but I believe newer GTRs have built in ethanol sensors and adjust the tune accordingly. they also have pumps made for alcohol fuels and are made for e85......

Another problem with modern sports cars is at high revs the knock sensors pickup strong combudmstiom or engine vibration and falsely read it as knock...

But the laws of physics are unbreakable and some superior programming can predict knock based on it'd precursors...IAT, AIR VOLUME, EGT, AMOUNT OF STATIC COMPRESSION AND VALVE TIMING LIFT AND DURATION...they can compute these things extremely fast and change the conditions to prevent knock...BMWs. N55 I believe does a simplified version of this which is why I personally have never heard of add n55 blowing up from detonation.

but like u said they don't know the octane, so they come from the factory most likely programmed to assume it's 91 aki (the min recommended fuel)...Probably also y they are getting much harder to tune effectively.
.