Nordschleife

Colin
Bear in mind that I am talking about Turbo cars with Motronic 7.x ECUs. These DO advance and retard the timing appropriately. The Motronic unit takes a little time to adjust, it may be imagination but I feel that its not until the car is onto its second tank of 100+ RON that maximum use is made of the fuel.
I understand about the Boxsters being the same speed at Watkins Glen. As far as I can recall, there is not a strait that is more than 5 kilometres long, which is what it takes to coax the ultimate top speed out of the Turbo cars.
Everytime I fill with 95 RON, which is all that is available in some areas of Europe, I DO feel that the whole performance of the car suffers, and its usually exacerbated by high ambient temperatures as well. Under theses conditions I do notice the engine tremperature increases more than when I am running on 98 or 100+ RON.

R+C

38D

I believe that my Boxster S also had Motronic 7.x. My point is that Porsche assumes some RON or MON rating in their programming. In the US, I would guess it's around 93. Anthing less that that, and the timing will retard. Anything more and you get nothing. I think the recommended RON is 98, so I can buy that 95 will reduce performance, but I wouldn't think that 100+ would increase it.

Btw, we ran the 2 Boxster S for 2 full days (4 run per day at ~20-30mins per run), so it had plenty of time to learn (I think I filled up the tank twice).

RJay

Hmmmm.... I wouldn't be surprised if the programming is different for the US and Europe.

Nordschleife

as i say, the difference between 98 and 100+ is only felt in the ability to pull top speeds. If your US cars have 'soft' speed limiters, you would run into them before you would notice the difference in performance, i would imagine

Patrick

http://www.prime-mover.org/Engines/G...es/octane.html

"HOW DO THEY GET OCTANE NUMBERS ABOVE 100?

Often it's done by pure extrapolation. A more reliable method, however, is through the use of so-called performance numbers. Briefly, these are arrived at by determining the instantaneous mean effective cylinder pressure (IMEP), using the fuel under test, at the highest boost that does not cause knocking. This number is then multiplied by 100 and the resultant is divided by the IMEP at the highest boost that does not cause knocking on the 100 octane equivalent fuel.

Note that, technically, there is no such thing as an octane number above 100. If you're at a party, avoid saying things like "110 octane gasoline" because people will get up and walk away from you. You should say, instead, "a gasoline with a performance number of 110." That will bring the help scurrying over with more champagne. "

Geo

OK, good idea, but this thread is just full of further misinformation.

If you really want to know about gasoline, go to the Gasoline FAQ:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

Specifically, if you're interested in understanding octane, octane numbers, anti-knock index (AKI), etc., go to page 3:

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

RON (Research Octane Number) and MON (Motor Octane Number) have absolutely NOTHING to do with the transmission type.

Happy reading.

Geo

This is a huge over generalization.

Although many use the term knock and detonation interchangeably, there are others that do not. It's important to know. Some define detonation as a runaway chain-reaction event and this is very bad.

As for knock being a good thing, I quote from "The Internal-Combustion Engine in Theory and Practice, Volume 2: Combustion, Fuels, Materials, Design" revised edition by Charles Fayette Taylor (this is a text book):

"Objection to Detonation. ...Detonation may lead to overheating of spark-plug points, with resultant preignition, that is, ignition before the spark occurs. Severe preignition causes loss of power and economy, unsatisfactory operation, and often damages the engine."

There is more I can cover and quote on this subject, but it will take a little research time that I don't have at 1 am (just got in from an Easter trip).

Bill935K3

Here is some interesting info I lifted of the VP fuel site. And some facts you all might find interesting about my old motor. I’ve been using their C12 for 6 years. In bad old day when we ran a 3.4 CIS, we finally ended up with two GM 300cc injectors over the top of our Euro CIS injection for enhancement under boost. I think we were at 65% duty cycle at 6500 RPM and 1.25 bar. We always stayed with the 3.4L because my mechanic liked the piston ring design better than the 3.6. More meat in case we did get some detonation and erosion at the piston edge. Once we got this motor refined we were getting in the low 500’s RWHP and a max service life of about 60 hours. We would tear down every winter and alternate light and heavy rebuilds. A light rebuild was pistons, rings, rod bearings, valve guides. Heavy added full sets of jugs, valve train etc. Now we have moved up to the big league with 3.8L and EFI. We stayed with the c12 as it is sold from bulk tanks in our area and due to this sales volume is cheapest of the race fuels around.
Interesting note the info below speaks of “peak cylinder pressure”. With our new motor this is the limiting factor. We can’t run more boost than we do due to the RPM range that we make peak torque at. If I understood the explanation right there is a calculation that can be done to arrive at PCP. If anyone has any info or links on this subject I love to read up on it
(all below info is from )http://www.vpracingfuels.com/index2....B7C86BA94CD299
C12 The best all around racing fuel made. Recommended for CRs below 15:1, satisfying the needs of 75% of today's race engines. One of the winningest fuels in racing history, including Modified Tour, GNN, D.I.R.T., Indy Lights, NHRA, AMA as well as other local and national championships across the U.S. and around the world.

Specification Sheet: VP C-12
Specific Gravity: .717 @ 60F
Lead: Leaded Color: Green Motor Octane: 108 MON
RVP: 7.3 Oxidation Stability (min.) 1440+
Distillation:
10% evap @131.0°F
50% evap @194.0°F
90% evap @228.0°F
E.P. @233.3°F Production: Elmendorf, Texas USA
FOUR FUEL PROPERTIES

Listed below are the four basic qualities of fuels. As in everything, there are trade-offs. You can't make a racing fuel that has the best of everything, but you can produce one that will give your engine the most power. This is why we produce different fuels for different applications. The key to getting the best racing gasoline is not necessarily buying the fuel with the highest octane, but getting one that is best suited for your engine.
1. OCTANE: The rating of fuels ability to resist detonation and/or preignition. Octane is rated in Research Octane Numbers, (RON), Motor Octane Numbers, (MON), and Pump Octane Numbers (R+M/2). Pump Octane Numbers are what you see on the yellow decal at the gas stations and represents an average of the two. VP uses MON because this test method is more prevalent in racing. Most other companies use RON because it is higher ad easier to come by. Don't be fooled by high RON numbers or an average. MON's are most important for a racing application, however, the ability of the fuel to resist preignition is more that just a function of octane.
2. BURNING SPEED: The speed at which fuel releases it's energy. In a high-speed internal combustion engine, there is very little time (real time - not crank rotation) for the fuel to release its energy. Peak cylinder pressure should occur around 20° ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure, which is what the rear wheels see.
3. ENERGY VALUE: An expression of the potential in the fuel. The energy value is measured in BTU's per pound, not per gallon. The difference is important. The air fuel ratio is in weight, not volume. Remember, this is the potential energy value of the fuel. This difference will show up any compression ratio or engine speed.
4. COOLING EFFECT: The cooling effect on fuel is related to the heat of vaporization. The higher the heat of vaporization, the better its effect on cooling the intake mixture. This is of some benefit in a four stroke engine, but can be a big gain in 2 stroke engines.

JCP911S

AMAN to that. Why just the other day I was explaining the antiknock properties of various branched chain hydrocarbons to a very attractive woman at the bar, and as soon as I used the term "110 Octane gasoline" she excused herself to freshen up, and never came back.

Now I know what I should have said....

Geo

Just say "I've got a Porsche."

Oh wait.... What did that survey say? Perhaps you should just have said you had a BMW or something.

SundayDriver

You should really read what I wrote before accusing me of generalizing. I was very specific that knock is a good thing from a HP standpoint. I did NOT say it was a good thing. Simply look at one of those many charts in the Taylor book (I am very familiar with it) and you can see that a sharper climb in combustion pressure will improve the efficiency of the combustion cycle. The downside, as I stated, is that it is very hard on parts. I never advocated intentionally running with detonation, unless you are willing to do the things they do with top fuel motors.

As far as your other post about transmission types, I could well be wrong, but I suspect not. Note (read again what I said) that I did not say the RON/MON was based on transmission type. Rather I was talking about the reason that the specs were set the way they were for the test. The CFR engine does not have, and has never had, a transmission attached and that has nothing to do with the test itself. Rather, I was reporting what I learned about the origins of the tests and the specs for RON vs. MON. That info came from some old timers from the fuel testing arena and I trust their stories and background as their professions made them part of the standards setting group for many years. If you have some insight that differs, I would love to know about it and the sources. Just what is it that makes you say that is not true?

Geo

From p3 of the Gasoline FAQ:

6.4 Why are two ratings used to obtain the pump rating?

The correct name for the (RON+MON)/2 formula is the "antiknock index",
and it remains the most important quality criteria for motorists [39].

The initial knock measurement methods developed in the 1920s resulted in a
diverse range of engine test methods and conditions, many of which have been
summarised by Campbell and Boyd [103]. In 1928 the Co-operative Fuel Research
Committee formed a sub-committee to develop a uniform knock-testing
apparatus and procedure. They settled on a single-cylinder, valve-in-head,
water-cooled, variable compression engine of 3.5"bore and 4.5" stroke. The
knock indicator was the bouncing-pin type. They selected operating conditions
for evaluation that most closely match the current Research Method, however
correlation trials with road octanes in the early 1930s exhibited such large
discrepancies that conditions were changed ( higher engine speed, hot mixture
temperature, and defined spark advance profiles ), and a new tentative ASTM
Octane rating method was produced. This method is similar to the operating
conditions of the current Motor Octane procedure [12,103]. Over several
decades, a large number of alternative octane test methods appeared. These
were variations to either the engine design, or the specified operating
conditions [103]. During the 1950-1960s attempts were made to internationally
standardise and reduce the number of Octane Rating test procedures.

During the late 1940s - mid 1960s, the Research method became the important
rating because it more closely represented the octane requirements of the
motorist using the fuels/vehicles/roads then available. In the late 1960s
German automakers discovered their engines were destroying themselves on
long Autobahn runs, even though the Research Octane was within specification.
They discovered that either the MON or the Sensitivity ( the numerical
difference between the RON and MON numbers ) also had to be specified. Today
it is accepted that no one octane rating covers all use. In fact, during
1994, there have been increasing concerns in Europe about the high
Sensitivity of some commercially-available unleaded fuels.

The design of the engine and vehicle significantly affect the fuel octane
requirement for both RON and MON. In the 1930s, most vehicles would have
been sensitive to the Research Octane of the fuel, almost regardless of the
Motor Octane, whereas most 1990s engines have a 'severity" of one, which
means the engine is unlikely to knock if a changes of one RON is matched by
an equal and opposite change of MON [32]. I should note that the Research
method was only formally approved in 1947, but used unofficially from 1942.

6.5 What does the Motor Octane rating measure?

The conditions of the Motor method represent severe, sustained high speed,
high load driving. For most hydrocarbon fuels, including those with either
lead or oxygenates, the motor octane number (MON) will be lower than the
research octane number (RON).

SundayDriver

So Geo, what is it you are trying to say that differs from what I asserted?

There were multiple ratings. RON became predominant in the US as cars moved to nearly 100% automatic transmission. The Germans found this was not the right rating for their vehicles. WOW - they were almost entirely manual transmission and they discoverd that MON more closely modeled their needs.

It is really nice that you can quote a bunch of text. How about adding something that has some meaning or actually supports your assertions.

BTW - Have you ever actually seen, let alone run one of those "Co-operative Fuel Research" engines you reference? Interesting that it has the initials CFR just like the test engines I operated as a student.

Geo

Wow Mark, I guess you must have read the word transmission somewhere in there that I don't see.

I suppose you're trying to assert because you have seen and used one of these engines and I have not that it's not possible I could know anything about the subject and that you are infinitely more correct. Not what I'd expect of you Mark.

As for quoting text and referencing the source, that is the mainstay of any research. Just because I'm not creating new knowledge doesn't mean I can't learn from the experts.