znod

Glad to have you jump in at any point ipse d. Gas can matter for sure. Generally, the better European gases are pretty high octane, but I don't recall how high. Unfortunately, I am stuck with measly 91 octane. And, I could not quess how additives would help or hurt or what is in any gas. I just don't pay attention. I just buy top-tier gas because the additives are supposed to promote cleaner engines, etc., but, as far as I know, not better acceleration.

znod

All of what you say is true. I sure wish we had some 550i meter men or women. It looks to me like the 550i's will be as fast as expected. For example, consider the following unadjusted 0 to 62.14 data from above:


0 to:...........0 to:...............550i...................Znod's 545i's Best 5--Unadjusted........Avg
100k.......62.14m...............5.5............... ....5.57.....5.50.....5.59.....5.55.....5.54...... 5.55

Had the 550i gotten a better start (or used a 1' rollout or a 5 mph rolling start--assuming it did not do so), then the 0-62.14 values for the 545i and the 550i would be rather similar--which would imply the sorts of 0-60 times that I got for the same tests as above (or slightly better):

.................................................. ............................Avg
0-60..........5.179...5.109...5.191...5.164...5.162. ..5.161

These are the kinds of times that I have been estimating for the 550i, although some are expecting faster times. Time will tell.

I do think that the 550i guys will need to figure out how to get the most from their cars and will have to "use" them enough to teach them a thing or two. And, I was thinking about what the worst possible case for my car would be. Oyster believes the 550i probably was tested in the area of 500' to 1,000'. So, I started wondering about my times in comparison to those of the 550i if I adjusted to only 1,000'. The pertinent comparisons are given below.

From above:..............................550i.........5 45i--Avg
Unadjusted--0.to.160k.............12.4..............12.31
Adjusted to 500'--0.to.160k......12.4..............12.05

New:.........................................550i. ........545i Avg
Adjusted to 1,000'--0.to.160k...12.4..............12.18 (estimated conservatively)

The implication is that my observations about the performance relationships between the 545i and the 550i would remain essentially unchanged after adjustment to the more conservative 1,000', rather than 500', although the magnitudes of the differences between the two cars would be smaller.

ipse dixit

Znod,

I don't think it is really proper to compare the test times in your 545i with the numbers that magazines (either US or German) produce with a 550i.

The 550i numbers achieved by magazines are from new cars, with new engines that have considerably tighter tolerances than your car, which has been broken in and the engine is much looser, allowing it to rev much more freely.

We'll just have to wait for a 550i owner to run in his/her car a bit (prob. 7500miles or 10,000km), buy a G-Meter and do some test runs.

znod

Well, the comparisons at least tell us about the difference in a new 550i and a slightly used 545i--given the test conditions. And, we don't really know how many miles the 550i had on it. And, we might as well say that it is unfair to compare because my car's unadjusted values have to be based on 91 octane at 1,600 ft'. If we continue your train of thought, we could never compare any cars except those where everything imaginable is held constant--even via times produced at a drag strip. Comparing things that are not identical is the name of the comparison game. We comparers do our imperfect bests because comparing real things with other real things is interesting and informative even though imperfect knowledge is obtained.

Please recall two comments I made above.

1. "But, all, please remember that I am not declaring a winner for my car (or any other 545i) versus any 550i. We still have much to learn about the 550i's."

2. "I don't think we will ever know much about relative quickness of the two cars, however, unless some of
us start testing 550i's. Same with SMG's and manuals versus Steps. I don't think the magazines are likely to provide as good an answer as we could through conscientious testing.

oyster

Maybe I can add something on the fuel matter. In Germany, the recommended fuel for the V8s is 98-octane SuperPlus (btw at 1,35 ?/liter), which would be the fuel used in the tests.

Magazines like AMS or auto zeitung get their test cars directly from the manufacturer, of course pretty new, but selected for quality too, and upper-class cars would be equipped to the max, thus gaining weight.

needforspeed

Znod - admire the scientific approach and thanks for adding the graph, funnily enough I drew a little graph with the same data prior to my post to you.

Statistical data is almost always manipulated to suit the user. So manufacturers will do various things to make their official performance statistics look as good as possible. Most magazine tests are less scientific and almost always show performance less than the official data.

For the data set you have used the 545 and 550's performance seems to be extremely close, but I think that the only conclusive statement you could make at the moment is that a 545 can be made to accelerate very nearly as quickly as a 550. If one wants to get REALLY picky then the only way to compare properly is to have the same driver run each car at the same time in the same conditions and with the same level of experience of the vehicle - not very achieveable. Even if you drag raced the cars 100 times, there would be a difference in respect of the drivers ability / approach / reaction time.

In terms of the graphical example - can you not plot distance vs time? Although the 'curve' between the data points would be interpolated this will be the most intuitive way to view things. I guess to do this you probably also need full data from a 550 with distance measurements as well as time.

znod

Thank you very much for the info. It is great to have you join in from Germany. May I recommend a meter for you? For comparative purposes, note that my car is pretty much maxed out weight wise--except for my after-market wheels and tires. Does the article indicate whether the 550i has the sport package for sure? And, does the magazine give an actual test weight for the 550i--with or without the driver? Does the car have comfort seats?

znod

Gosh, I hope not. (but, your point certainly is valid many, many times). I am doing a variety of things to present somewhat conservative results for my car. For example, I always chose the least favorable of the data sources for weather information. I generally emphasize averages of best tests. Finally, we have started adjusting our data to 500' rather than to sea level.

Be aware, though, that I have had many crummy passes. To some extent, I agree with you about manufacturers except BMW, for example, gives pretty darned conservative claims. I know of one good example where the magazines could not quite get the manufacturers claim--the C5 Z06--on which Chevy claimed zero to 60 of less than 4 (one magazine got 4.0). But, many have achieved the not-overly-hard-to-accomplish feat of 0-60 in less than 4.0.

Using the Pro RR I would not have to interpolate anything. I can get time/speed to/for "any" distances for time increments as small as .01 seconds over the whole 1/4 and beyond. Time to distance would be a great way to do comparisons, but, for example, even drag strips provide only limited time to distance data. And, magazines seldomly provide much in the way of time-to-distance data.

Thank you for your thoughts. What kind of meter are you going to buy?

cobradav

Offered in the respect of comparing octane ratings in Europe and US. However, it does include a discussion on the merits (or not) of higher octane gasoline (or petrol )

Octane
Octane is measured relative to a mixture of isooctane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane. A complementary standard for diesel fuel is the cetane number. A low octane rating means that the fuel has a high tendency to autoignite, which is undesirable.

Measurement methods
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON), which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "normal" gasoline in the US and Canada, would be 91 in Europe.
The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, straight ethanol, Avgas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher. Typical "octane booster" additives include tetra-ethyl lead and toluene. Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition.


Effects of octane rating
Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression ratio only governs the maximum compression that can be achieved).

It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist spontaneous ignition (pre-ignition = engine knock) as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.

A simple explanation is the carbon bonds contain more energy than hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the Octane rating. A premium motor fuel will often be formulated to have both higher Octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content. The reason for this is that ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl radical for a H hydrogen which transforms the gas C2H6 ethane (which is an alkane) into ethanol (which is an alcohol). Note that to a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high Octane fuels that carry less energy per liter than lower Octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

Using a fuel with a higher octane lets an engine run at a higher compression without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure which is a function of elevation and weather conditions.

Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine power is a function of the fuel as well as the engine design and is related to Octane ratings of the fuel... power is limited by the maximum amount of fuel-air mixture that can be stuffed into the combustion chamber.

Many high-performance engines are designed to operate with a high maximum compression and thus need a high quality (high energy) fuel usually associated with high octane numbers, and thus demand high-octane premium gasoline.

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is mostly false?engines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal.
Using high octane fuel for an engine makes a difference when the engine is producing its maximum power. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. These conditions are present only when the accelerator is totally depressed.

When this occurs, if a fuel with below recommended octane is used, then the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a white paper that gives an example: http://dinancars.com/whitepapersFile.asp?ID=9 . In this example the engine maxium power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 HP: 280 VS 291). If the engine is being run below maxium load then the difference in octane will have even less effect. The example cited does not indicate at what elevation the test is being conducted, and what the barometric pressure is. For each 1000 feet of altitude the atmospheric pressure will drop by a little less than 1 PSI. An engine that might require 93 Octane at sea level may perform at maximum on a fuel rated at 91 Octane if the elevation is over say 1000 feet.

The octane rating was developed by the chemist Russell Marker. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.

grogan545

Thanks for the information on octane.I was wondering why Znod only has 91 octane available in his area(1500' altitude).I have been using 94 octane in my car for the last 6 weeks and did not notice a difference in performance or mileage.I guess i'll go back to 93 octane since it appears to be fine for my car.