# Fuel Octane Specifications for the Phaeton (includes TB 01-06-02, Fuel, Poor Quality)



## SunnyD21 (Mar 21, 2005)

*Octane Question (revisited)*

I had posed the question a few months back and I'm curious to uncover people's findings. The thought was to see what happened in both performance and fuel economy when filling the tank with 89 or even 87 octane fuel. 
Since that original discussion, I've been filling my V8 with 89 and have experienced absolutely no apparent difference in performance or fuel efficiencies from when I was using "super". Is it just me or is "super unleaded" one big marketing ploy?


----------



## GripperDon (May 9, 2005)

Since my manual mentioned 97 octane I was considering adding a "Octane Booster' to the 91 octane which is the highest I can buy locally. Except for one local that sells 105 octane for $6 per gallon blending the two to get the 97 "preferred octane" it comes out to about $4.25 per gallon. so the booster is considerably less expensive, Comments Please!


----------



## DCubed (Oct 25, 2004)

*Re: (GripperDon)*

97 octane? I might have to check the manuals, the fuel door states 91 minimum, but I know people put 87 in our loaner all the time, and it runs with no difference in performance, but when someone forgets to fill it, in we go with the 91.


----------



## GripperDon (May 9, 2005)

Sorry! Went and looked at my fuel door again again it says Mininum ROM 95, and (R+M)/2 for 91 octane


_Modified by GripperDon at 11:18 PM 6-15-2005_


----------



## PanEuropean (Nov 3, 2001)

*Re: Octane Question (SunnyD21)*

I've been filling my W12 with regular grade gasoline ever since David Cowan told me that his W12 runs great on regular grade. The door sticker gives an allowable range of octane ratings that can be used in the car. The lower of the two numbers is the minimum octane that is required for satisfactory performance. We should not ever use fuel with a lower octane number. The upper of the two numbers is the fuel that is recommended if you want to get the full performance capability of the engine.
I don't plan on driving my W12 anywhere near its design speeds, and it seems to run just fine with the regular grade (I don't accelerate aggressivly, or demand top engine output), so, I'm happy to stick with regular. If I notice any engine related problems - meaning, if the car generates a fault code indicating that a knock (pre-ignition) was detected - then I will move up one grade to a mid-grade gasoline.
Michael


----------



## dcowan699 (Nov 22, 2004)

*Re: Octane Question (PanEuropean)*

I still have no problems with using regular octane gasoline. No pings and the performance is just fine and my mileage is not bad either. I get 21 hwy and 16 around town.
Quite honestly I've never used premium grades in any vehicle I own.


----------



## Franklin2 (Apr 28, 2005)

*Re: Octane Question (PanEuropean)*

Michael, As I recall from spending several years in Geneva, the octane ratings in Europe are higher than in the USA due to a method difference in measuring octane. Is it possible the some of these fuel door European labels mentioning 97 and 95 octane were put onto USA destined cars by mistake. Mine says 91 octane. 
Larry


----------



## PanEuropean (Nov 3, 2001)

*Re: Octane Question (Franklin2)*


_Quote, originally posted by *Franklin2* »_As I recall from spending several years in Geneva, the octane ratings in Europe are higher than in the USA due to a method difference in measuring...

That is correct.
There are two methods that can be used to rate the octane value of gasoline - one is called Research Method, and the other is called Motor Method. These two methods are defined in the American Society for Testing and Materials (ASTM) protocols d 908 and d 357, respectively.
Each method has its own advantages and disadvantages. As a broad generalization, the motor method captures the gasoline's performance at high engine speeds and loads, and the research method at low speeds. The octane rating on American gasoline pumps is usually the average of the research and motor octane numbers, which is sometimes called the anti-knock index. In Europe, pumps have traditionally displayed the research octane number. _(citation: C. A. Amann. The Automotive Spark-Ignition Engine – An Historical Perspective.)_
In the picture below, which shows the fuel sticker on my North American W12 Phaeton (disregard the writing in French - Canada is bilingual - otherwise, it is the same as a USA sticker), you can see that Volkswagen provides guidance to owners using both methods - the Research Method, which is abbreviated to RON (Research Octane Number), and the 'anti-knock index' (the average of the two methods), which is abbreviated to R+M/2 (Research Method plus Motor Method, added together, then divided by two).
This alone would be nice and simple to understand, except that there is another quite recent complication added: The Phaeton engine can accept and run quite well on fuels that span a fairly wide range of octane measurement. So, VW gives two numbers for each measurement method: The lower number is the lowest allowable fuel rating that you can put in the vehicle, and the higher number is what you should put in the vehicle if you want to demand (and get) 100% of rated engine power.
This results in a sticker (below) that is decoded as follows:
*If the fuel retailer uses RON as the rating method, 91 is the lowest acceptable rating for everyday use, and if you want to demand and get full rated power from the engine, you should put 95 in it.
If the fuel retailer uses R+M/2 as the rating method, then 87 is the lowest acceptable rating for everyday use, and if you want to demand and get full rated power from the engine, you should put 91 in it.*
If a vehicle has a fairly low power engine in it - meaning, the power output of the engine is sufficient to move the vehicle around, but there is no surplus of power provided (a Golf with a 1.2 litre engine would be a good example of this - it can barely get out of its own way), then you will only see one number provided. If the vehicle is fitted with an engine that can produce far more power than is actually needed to move the vehicle around (a Phaeton with a V8 or W12 is a perfect example of this - heck, a 3.2 V6 engine is more than sufficient for a Phaeton), then the manufacturer will normally provide a range of numbers, in order to allow the owner to choose between economy and maximum performance. The option to put different grades of fuel into the Phaeton, depending on what your needs that week may be, is a fairly recent development that is a direct outcome of the very sophisticated engine management computers that are fitted to modern, high performance engines.
Lastly - there is the question "What method is this fuel retailer using to rate the octane of what I am about to pump into my Phaeton?" There is an easy way to figure that out. Look at the numbers given for both regular and super at that gas station. Determine which of the two scales (RON or R+M/2) on your Phaeton fuel sticker that *both *the regular and super grades will fit into. That is the method they are using. It's that simple.
Michael
*North American W12 Phaeton Fuel Specification Sticker*
This sticker gives specifications for both measurement methods








*European W12 Phaeton Fuel Specification Sticker*
This sticker only gives specifications for the RON measurement method.
Why the difference between RON spec for a North American W12 (shown above) and RON spec for a European W12 (shown below)? It's because the two engines have different performance characteristics, as defined by the software in the engine management controller. It's also because the North American engine will never be called upon to deliver the horsepower needed to propel the car at 150 MPH speeds, because the Phaeton is limited (governed) to a maximum of 130 MPH in North America. For this reason, a lower 'minimum' octane fuel can be used in the North American engine (91, vs 95 for the Europeans), and there is no point at all in wasting money on fuel with a RON of higher than 95 in the North American engines, because it won't do anything for you. If you put "Sunoco 94" (the equivalent of RON 98) in your North American W12 Phaeton, you are just wasting money, plain and simple. But - if you want to cruise at 150 MPH on the Autobahn with your European W12 Phaeton, then "Sunoco 94", or some other fuel with a 98 RON, is the price of admission to the left lane.


----------



## car_guy (Aug 19, 2005)

*Re: Octane Question (PanEuropean)*

I guess I can't resist bringing this subject up again but I happened upon this item on the Web: 

Demystifying Octane Ratings (on Cars.com)
http://www.cars.com/carsapp/na....tmpl
A paragraph from that article:

"If your car requires high-octane gasoline and you habitually use regular gas because the engine exhibits no sign of knock, you’re outsmarting yourself. Most modern, computer-controlled engines include a knock sensor that detects knock and retards the ignition timing, causing the spark plugs to fire slightly later in the cycle. This typically prevents abnormal combustion and knock, which allows vehicles specified for premium fuel to run on lower-grade gasoline if it is all that’s available. While this removes the immediate hazard, it’s a bad idea to make a habit of running a vehicle on gasoline of lower-than-recommended octane. Retarding the spark causes a richer fuel/air mixture, which decreases fuel economy, increases emissions, causes the engine to run hotter, and reduces the longevity of both the engine itself and the catalytic converter. The money you save by pumping low-grade fuel into a car that demands higher octane is lost anyway, in decreased fuel economy and possibly gradual damage. "


----------



## riccone (Nov 11, 2004)

*Re: Octane Question (car_guy)*

I have been seeing this issue raised for longer than I can remember; it is the "Energizer Bunny" question. I have NEVER used Premium fuel in any car. .. NEVER. 
As the late Johnnie Cochran once said during a famous trial;
"If it don't ping. . . .buy a cheap ring"


----------



## car_guy (Aug 19, 2005)

*Re: Octane Question (riccone)*

I plan to keep my Phaeton for a long time. It doesn't seem worth the gamble to save 6.5% on the fuel price while sacrificing 7% in octane. We're talking about $150 a year (15,000 miles driven) on a $70,000 - $100,000 car.
If you keep the car for five years, you've saved about 1% of the $70k purchase price. And only that much if you don't suffer any MPG reduction, as the article indicates you will. Every time I put my foot to the floor (okay, not that often), I also don't want to worry that I might be doing some harm or not getting all the performance I paid for.
I believe what the article says: If you do this, you're only outsmarting yourself.


----------



## PanEuropean (Nov 3, 2001)

*Re: Octane Question (car_guy)*

Steven:
What you say may be correct for the V8 engine, although I don't know what the fuel specification for the North American V8 is. In the case of the North American W12 (the BAP engine), the fuel specification is anything the driver wants between regular grade (87 Anti-Knock Index) and premium grade (91 Anti-Knock Index). The only comment that VW makes is that if you choose to use regular grade, the engine will not make full rated horsepower.
The European W12 is a different engine - although it has 12 cylinders, and probably has a lot of parts in common with the NAR W12, it's not a BAP engine, it has a different designation. It is also built to conform to different (stricter) emissions requirements. This likely explains why the European fuel specification for the engine is different.
Michael


----------



## dcowan699 (Nov 22, 2004)

*Re: Octane Question (PanEuropean)*

I continue to have absolutely no problem with 87 octane. I run it constantly and see no problem. I get 21 on the highway and around 15 or 16 around city.


----------



## iluvmcr (Jan 14, 2005)

*Re: Octane Question (PanEuropean)*

I drove 900 miles from Indiana to New Hampshire and then back in my V8 Phaeton and decided to use 87 octane fuel for the first time for the entire trip. I drove it easy - 70mph steady. No apparent knock, degredation of fuel milage, or performance loss (although there must have been some performance loss). So then I decided to drive with max acceleration, off the line like a jack-rabbit at every stop light, and still no apparent difference - no check engine light or apparent knock (pre-ignition).
Michael, doesn't the check engine light come on if knock is detected?








I'm amazed that an engine with 11.5:1 compression can handle 87 octane fuel so well.







Now that I'm done with my little experiment, I'm going back to 91 octane or better fuel.


----------



## PanEuropean (Nov 3, 2001)

*Re: Octane Question (iluvmcr)*


_Quote, originally posted by *iluvmcr* »_Michael, doesn't the check engine light come on if knock is detected?









Not unless the pre-ignition problem is so severe that the engine management controller cannot control (eliminate) it by adjusting the behavior of the engine. In other words, if you fill up with fuel that has an 87 anti-knock index, or (R+M)/2, the engine controller has the capability to deal with that, which is why the manufacturer approves that fuel for use in the vehicle. If you fill up with fuel that has a 83 anti-knock index, the controller won't be able to cope with that at all, the engine will enter 'limp' mode, and you will see an *EPC* light (Engine Power Control, or engine management) come on - not a MIL.
Remember, the MIL (Malfunction Indicator Light), which was formerly known as a CEL (Check Engine Light) is only present on USA specification cars. If the MIL light illuminates, it does not mean that there is a problem with the engine - instead, it means that there _*could be*_, or _*could have been*_ (at some time in the past) a problem with one of the many US Government mandated emission control systems. Heck, a loose gas tank cap will trigger a MIL, although it won't affect function of the car in any way.
If there is actually a functional problem with the engine, you will see the EPC light, not the MIL. It is possible that some conditions could trigger both lights. For example, if you filled the car up with fuel that has a 83 anti-knock index, not only would the engine have severe difficulty operating (and thus generate an EPC light), the fuel would not be efficiently burned, due to the pre-ignition, and this would increase vehicle emissions - thus triggering a MIL as well.
Michael


----------



## jmuoio (May 30, 2006)

*High Octane Fuel*

I found a place that sells 110 octane fuel here in San Diego. I was a little nervous about the stuff, so I only put in a 1/4 mixture to get a boost. I used a 1/3 mixture in my BMW 750. WOW. Unfreakingbelieveable difference in engine performance. I was shocked at how much more torque the engine had, and how much quieter it ran in both cars. In the BMW, the stuff makes the engine throw you back in your seat, even at the 1/3 mixture I used for it.
Some knowledgeable individuals warned me that it would make the engine run too hot. However, the water temperature never budged from 200F the whole time, so I'm not sure if that concern was valid.
Anybody else ever run high-octane fuel, or know where else to get it? Does anyone have any qualified input on what impact this may have on the W12? I'm not going to run it all the time, but I do like to take the car out on a drive on open road and I'm curious what would happen with a full strength tank. But, given the cost of a W12 engine, I'm not willing to risk it just for fun, unless someone qualified can give me some insight.
Thanks.


----------



## chrisj428 (Feb 26, 2005)

*Re: High Octane Fuel (jmuoio)*


_Quote, originally posted by *jmuoio* »_Some knowledgeable individuals warned me that it would make the engine run too hot. However, the water temperature never budged from 200F the whole time, so I'm not sure if that concern was valid.

But what did it do to exhaust and combustion chamber temperatures? See the thread about how much replacing an oxygen sensor on a W12 costs & ask yourself: "Is it _really_ worth it???"


----------



## PanEuropean (Nov 3, 2001)

*Re: High Octane Fuel (jmuoio)*

The W12 engine in the NAR Phaeton (the BAP engine) can run on either regular or super fuel. It is the choice of the owner what to put in it - if you put regular fuel in it, the engine will not develop full horsepower, but it will not be harmed either. There is an extensive discussion about fuel specifications for the Phaeton engines elsewhere.
I don't know a lot about fuel specifications, however, I think that the octane rating is primarily a measure of the anti-knock (resistance to pre-ignition) rating of the fuel - I don't think it is a measure of the calorific energy contained in the fuel. The engine controller in the Phaeton will adapt automatically to various octane ratings that are available at the pump in North America. I rather suspect that it will disregard octane ratings higher than what is listed on the fuel cap door sticker.
Michael
*Fuel Specification for NAR W12 Engine (BAP engine)*


----------



## GripperDon (May 9, 2005)

In a nut shell the higher octane fuel will allow the engine spark advance to maximize. This will ignite the fuell earlier in the power sstroke and provide aN INCREASE IN POWER however the engine will not be hurt. Cylinder Temperature and pressure will increase. But that is why we have thermostats to provide more coolant flow and maintain proper opeating tempoerature. No effect on the oxygen sensor. The cat converter will also not be effected. 
It's a great engine and capable of handeling the small increase in effective power.
Enjoy


----------



## PanEuropean (Nov 3, 2001)

*Re: (GripperDon)*

Hi Don:
Thanks for clarifying that.
Would it be reasonable to assume that the engine control unit will only advance the spark timing 'so far' - in other words, if you put the top grade of fuel available at a normal gas station in the car, and the car runs fine on that (meaning, the engine advances the spark timing as far as it wants to), then there would likely be no difference if you put an even higher octane level fuel in?
What I am getting at is this: I am guessing that the ECU will only advance the spark timing up to a certain point, no matter even if you put rocket fuel in the car. Is that a correct guess?
Michael


----------



## GripperDon (May 9, 2005)

YES, A combination of A Knock Detector and the ECU's look up table. The Knock detector says no ping go t o the highest value in the look up table. A 150 octane aviation gas will most likely be the same spark advance as a 110 octane. I would really be a bit suprised that anything over 100 octane gives much more advance.


----------



## deepak.tripathi (Apr 14, 2006)

*Shell V-Power 99 RON Petrol*

I have switched from BP Ultimate Unleaded to Shell V-Power (99 RON) in the past fortnight and the engine and acceleration seem to be smoother. 
Is V-Power a good fuel in the long run? Or is it better to continue using BP Ultimate, which is I think 98 RON?


----------



## GripperDon (May 9, 2005)

Wish we had it here!


----------



## DCubed (Oct 25, 2004)

*Re: (GripperDon)*


_Quote, originally posted by *GripperDon* »_Wish we had it here!

European fuel is measured differently than american fuel, I think he is talking about the difference of 92 and 93 octane IIRC....or 91 and 92.....

Correct me if I am wrong though....
They use research method only....we use research+motor method/2=us octane measurement.


----------



## PanEuropean (Nov 3, 2001)

*Re: Shell V-Power 99 RON Petrol (deepak.tripathi)*

To the best of my knowledge (wich is not much), RON, or Research Octane Number, is a measure of the ability of the fuel to resist pre-ignition (sometimes referred to as detonation, or knock) within the engine. VW puts a specification for the minimum required RON on the inside of the fuel filler cap. 
I don't think there is much benefit from running a higher RON fuel than VW specifies, although you never know. Perhaps the engine controller is noticing that the fuel is more knock-resistant and as a result, it is adjusting the engine operating specifications to take advantage of that.
Those who have the W12 engine are given a choice of either running 91 RON or 95 RON. If the owner wants to achieve full rated power from the engine, 95 RON is required. If the owner is willing to accept a slight reduction in total horsepower produced, 91 RON is perfectly acceptable. Somehow, the engine is able to determine what the octane of the fuel being used is, and adjust things accordingly so that it runs perfectly well on either flavor.
Michael


----------



## deepak.tripathi (Apr 14, 2006)

*Re: Shell V-Power 99 RON Petrol (PanEuropean)*

Thank you, Michael.


----------



## Realist42 (May 14, 2006)

*Re: Shell V-Power 99 RON Petrol*

What Michael says is all true, however all modern engine management system can advance the ignition beyond the factory optimum value, with this you can see up to 10% improvement in bhp by using a higher octane fuel, as well as increased torque and engine responsiveness.
Depending on how quickly the engine is set to notice and react to better fuel, and this is sometime very slow, it can take a tank or two until you see the full effect. 
What it ultimately comes down to, and I had a Mercedes that had an Optimax addiction, if if you like the way the car feels with the other fuel, the stick with what you like.
Shell do put other additives in to the fuel to improve the combustion curve and ensure a smooth, quick and even burn of the fuel, and reduce soot etc. It is a matter of taste...
regards
Johan


----------



## Rowayton (May 29, 2004)

I'm no engeneer but it would seem to me that there would be no need for knock sensors to have memory. The engine management system is designed to constantly monitor the knock sensors in real time. The CPU adjusts the ignition curve instantanoiusly. Knock detection is more than fuel octane management. The CPU has no idea of what octane fuel you have in your tank. Many things like temprature, humidity and altitude, just to name a few, all come into play. Automotive manufactures state optium octane numbers so that their engines, as designed, can better meet an intended design spec both for power and emissions. It would seem that factory CPU's can dumb down an engine (if needed to avoid knock and potential engine damage) but very few if any should be able to smarten one up. Lower octane and potential knock equals less power and efficency as engine timing has been adjusted to compensate to avoid damage. Higher octane equals the engines ability to meet, not exceed, its engineered design spec. Think of your engine as if it were a customer in a resturant. If you asked for a steak and the waiter brought you a hot dog you could eat it. It may not kill you as food is food but you asked for steak. 
RB


----------



## car_guy (Aug 19, 2005)

*Re: Shell V-Power 99 RON Petrol (Realist42)*


_Quote, originally posted by *Realist42* »_What Michael says is all true, however all modern engine management system can advance the ignition beyond the factory optimum value, with this you can see up to 10% improvement in bhp by using a higher octane fuel, as well as increased torque and engine responsiveness.


I've never heard this before. May I ask what the source of this information is?
My understanding is that a car that requires only regular gas (say 87 U.S. method) does not benefit in any way from higher octane gas as long as the same detergents are in the regular as in the premium. 
I've never heard that a car that requires premium (say 92-93) benefits from anything higher.


----------



## deepak.tripathi (Apr 14, 2006)

*Re: Shell V-Power 99 RON Petrol (car_guy)*

I have just checked inside my fuel cap. The RON range advised is 95-98. For a fortnight, I have been using 99 RON Shell V-Power petrol and my impression is that the drive and acceleration are smoother compared to BP Ultimate Unleaded of 97 RON grading. Micheal has given his insight into it, which I appreciate. 
I have highlighted the word impression in the above paragraph, because I agree with those who suggest that in situations like this, one's mind likes to believe what it has selected in the first place and tries to rationalise that choice. This is why I started this thread, to hear from those who may know more than I do.



_Modified by deepak.tripathi at 5:10 PM 10-7-2006_


----------



## PanEuropean (Nov 3, 2001)

*Re: Shell V-Power 99 RON Petrol (deepak.tripathi)*

There is always the possibility that whatever liquid happens to be in the '95 octane' underground tank at the service station might not be exactly 95 octane. In other words, maybe due to age of the fuel, little mishaps that happen during transport and storage, stuff like that, what comes out of the end of the 95 octane hose might only be 94 octane or similar.
If that is the case, then putting a higher rated fuel (e.g. 99) in the vehicle might result in the car actually getting something that meets or exceeds the 95 octane specification, and this would account for the performance improvement that Deepak has noticed.
I'm quite startled that the VW recommended octane range (RON, the European measurement) for the V6 petrol engine is 95 to 98. That's considerably higher than the VW recommended octane range for the W12, which is 91 to 95. I guess that the V6 engine is a more sophisticated engine than the W12, in the sense that it requires a higher specification of fuel to deliver peak performance. Perhaps it is a newer design.
Michael


----------



## deepak.tripathi (Apr 14, 2006)

*Re: Shell V-Power 99 RON Petrol (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_There is always the possibility that whatever liquid happens to be in the '95 octane' underground tank at the service station might not be exactly 95 octane. In other words, maybe due to age of the fuel, little mishaps that happen during transport and storage, stuff like that, what comes out of the end of the 95 octane hose might only be 94 octane or similar. 
 
That is a very good point, Michael, and would appear to explain what you say below. 

_Quote »_ If that is the case, then putting a higher rated fuel (e.g. 99) in the vehicle might result in the car actually getting something that meets or exceeds the 95 octane specification, and this would account for the performance improvement that Deepak has noticed. 
I'm quite startled that the VW recommended octane range (RON, the European measurement) for the V6 petrol engine is 95 to 98. That's considerably higher than the VW recommended octane range for the W12, which is 91 to 95. I guess that the V6 engine is a more sophisticated engine than the W12, in the sense that it requires a higher specification of fuel to deliver peak performance. Perhaps it is a newer design.
Michael
 
In answer to your allusion to the engine of my car being more sophisticated, I would say it was registered new on 31 January 2005 and, I believe, would be one of the last front-wheel drive 3.2 V6 petrol cars before the introduction of 4-Motion. I know not whether this has any significance for the engine being more sophisticated.


----------



## Realist42 (May 14, 2006)

*Re: Shell V-Power 99 RON Petrol (car_guy)*


_Quote, originally posted by *car_guy* »_
I've never heard this before. May I ask what the source of this information is?
My understanding is that a car that requires only regular gas (say 87 U.S. method) does not benefit in any way from higher octane gas as long as the same detergents are in the regular as in the premium. 
I've never heard that a car that requires premium (say 92-93) benefits from anything higher.

Since the arrival of 'premium fuels' here in the UK of the last years, various car magazines have done trials with the fuels. The fill the car up with the fuel run it on a test route, and then stuck it on a rolling road. All cars so better than manufacturers figures with the premium fuels, some more than others. So, even if the cars were rated at RON 95, they gave more BHP using a RON 97 - RON 99 fuel...
Here is one example: http://www.thorneymotorsport.c...c%3D1 
rgds
Johan


----------



## Realist42 (May 14, 2006)

*Re: (Rowayton)*


_Quote, originally posted by *Rowayton* »_I'm no engeneer but it would seem to me that there would be no need for knock sensors to have memory. The engine management system is designed to constantly monitor the knock sensors in real time. The CPU adjusts the ignition curve instantanoiusly. Knock detection is more than fuel octane management. The CPU has no idea of what octane fuel you have in your tank. Many things like temprature, humidity and altitude, just to name a few, all come into play. Automotive manufactures state optium octane numbers so that their engines, as designed, can better meet an intended design spec both for power and emissions. It would seem that factory CPU's can dumb down an engine (if needed to avoid knock and potential engine damage) but very few if any should be able to smarten one up. Lower octane and potential knock equals less power and efficency as engine timing has been adjusted to compensate to avoid damage. Higher octane equals the engines ability to meet, not exceed, its engineered design spec. Think of your engine as if it were a customer in a resturant. If you asked for a steak and the waiter brought you a hot dog you could eat it. It may not kill you as food is food but you asked for steak. 
RB 

I am no automotive engineer either, but a friend of mine has a hobby of programming ECU, and has explained it all to me, not that I can recall it all, but apparently it is safer for the engine to slowly adapt to better fuel, a certain amount of inertia in the system weeds out fluctuations and gives more even performance... I would have to mention that he is quite mad, as he drives a Westfield with a Mazda RX7 rotary engine in it... Mad







http://en.wikipedia.org/wiki/Westfield_Cars 
Not his car, but still just a mad http://locostbuilders.co.uk/upload/2pic1.JPG


----------



## sidcup-jon (Mar 31, 2006)

*Re: Shell V-Power 99 RON Petrol (deepak.tripathi)*

I am no petrol head,more of a diesel junkie.But I think I have a rough idea what you guys are talking about.
I remember from some old Audi brochure,the rated BHP of their V6 engine and above were developed by using a 97 RON fuel.At the bottom of the spec sheet there is also a foot note says that a lower Ron of 93 may also be used with a slight reduction in power with no adverse effect to the engine.
You guys are lucky,you can tweak your engine simply by switching fuel.
Jon


----------



## sidcup-jon (Mar 31, 2006)

*Re: Shell V-Power 99 RON Petrol (sidcup-jon)*

I would like to add roughly what I remember from the brochure.I think this relates to the 4 cylinders petrol engine.
If either 95 or 93 Ron fuel are not availble,91 Ron may also be used,but prolong use is not recommended.( This is UK spec Brochure ).
Jon


_Modified by sidcup-jon at 6:56 PM 10-7-2006_


----------



## GripperDon (May 9, 2005)

Well I am sure you were waiting for this.
I was a Automotive Engineer designing both Diesel and gasoline fuel injections and we use a running average of "Hits" from the knock detector. If the vehicle had a turbo the running average was very short so it could react to the boost and regulate the waste gate. Every engine had it's own averaging time which was controlled by inputs of temperature and throttle position. WOT for example reduced the time duration of the averaging period. Actually this "time" was a # of Crank revolutions.


----------



## deepak.tripathi (Apr 14, 2006)

*Re: (GripperDon)*

Don
I am NOT an engineer and you completely lost me there.


----------



## sidcup-jon (Mar 31, 2006)

*Re: (GripperDon)*

I am no expert ,"Knocking" is that anything to do with compression ratio.A quick browse in the Phaeton and Touareg 3.2 V6 engine spec,the Phaeton has a higher ratio of 11.3:1 as compare to 10.8: for the Touareg.I assume the lower ratio is set up to suit the Touareg off road purpose.
I remember in the past when the oil company withdrew the leaded petrol from the pump,a quick fix for cars that can only run on leaded petrol was to fit another head gasket the engine to stop the knocking,I presumed this is to lower the ratio.( Please correct me if I am wrong ).
I like diesel engine not only for the fuel economy but also for the stonking torque and longivity of the engine.I will miss the constant knocking if I drive a petrol car.
Cheers Jon


----------



## jmuoio (May 30, 2006)

*Re: (GripperDon)*

Thanks for all the knowledgeable response to my posting. It's nice to have a bona fide discussion forum.


----------



## jmuoio (May 30, 2006)

*Re: Shell V-Power 99 RON Petrol (deepak.tripathi)*

I'm in so Cal, and I tried the Shell V-Power (91 Octane, R+M/2 method) here and something about it makes my W12 "burp" during idle at a definite interval. I don't know if it is the methanol content here in California, or what. I've stopped using it and will always try to stick with Chevron or Mobil, which mine likes.


----------



## GripperDon (May 9, 2005)

The "Knock" has a couple of forms but basically when a gas engine fires the spark plug "TOO SOON" you get a "Knock" The "Knock" is the result of the expanding gasses in the cylinder being forced to compress as the engine piston was still moving to compress the gasses within the cylinder rather than letting them expand to provide power.
The timing of this spark plug event is variable and is adjusted to account for the speed that the flame front moves through the combustible gasses. 
It is not at all unusual to trigger this event before the piston reaches top dead center in order to extract the most power from the combustion event. The pressure, temperature, fuel and additives, combustion chamber configuration, etc. all have effects on when to trigger this event. These are stored in a sort of look up table within the ECU Engine Control Unit) The ECU tells the spark plug when to fire based upon when the engine operation is occurring as per the look up table. However the table is a sort of fallback basic guide so to speak and can be adjusted or trimmed or changed to a degree by inputs from things like throttle position etc. But if the over ruled event timing should cause a knock then the timing is reduced so the knock is eliminated.
This is really a rough outline. Some look-up tables a include as few as 5 factors and some can go to a dozen or more. The algorithm of how the look up table is used and the "weighting" of trim variables is a selection made at the time the ECU is "set"

The knocking of a diesel engine is a whole different matter. The Diesel as you know has a Wide Open Throttle (WOT) all the time and power is varied by changing the amount of fuel used for each combustion event. The fact that the cylinders always have normal atmospheric pressure in them is one of the advantages of Diesels, they have no pumping losses as do gasoline engines. 
The fuel being "ignited" when it is injected into the cylinder just before the TOP dead center position of the piston. The combustion is typically more rapid than for gasoline and typically is heard as a knock of the engine. This increased rapidity of flame from velocity is related to a number of items a couple being the much higher temperature and pressure in the combustion chamber when the fuel is injected ( hot enough to ignite it without a spark plug)




_Modified by GripperDon at 4:59 PM 10-8-2006_


----------



## PanEuropean (Nov 3, 2001)

*Re: Shell V-Power 99 RON Petrol (jmuoio)*


_Quote, originally posted by *jmuoio* »_ ...I don't know if it is the ethanol content here in California, or what...

That raises another concern about fuel quality for forum members who live in the United States. In Europe and Canada, automotive fuel specifications are set at the federal level, so they are the same all across a country. In America, auto fuel specifications can be set at the state or local level, and there are about 50 different specifications in America.
In some areas (notably around Chicago), the fuel (any octane) has a higher ethanol content than VW recommends, and this leads to problems with (for example) starting hot W12 engines in the winter after a brief shutdown, say, 5 minutes or so.
About the only workaround we have discovered so far is to buy fuel that comes from a different refinery.
Michael


----------



## PanEuropean (Nov 3, 2001)

*Re: Shell V-Power 99 RON Petrol (PanEuropean)*

Attached is a TB (Technical Bulletin) that VW of America promulgated last year after investigating the problems that Chicago area W12 owners were having with starting the engine, when hot, in the winter, when the engine had been off for 5 minutes or less.
It's kind of a vaguely worded document, but the bottom line seems to be that if the car isn't running right on what you are putting into it, try changing your refinery.
Michael


----------



## NorCalJason (Sep 26, 2008)

*Re: Shell V-Power 99 RON Petrol (PanEuropean)*

Most ECU's cannot take advantage of increased octane.
Engines are designed to operate at a specific octane level (Octane = slower burning fuel = less energy).
So, if your engine was designed to run off of 91 octane, running 100 octane will DECREASE engine performance.
I know I know, but all that marketing by oil companies tells you otherwise.
Most ECU's today operate in two modes. Closed, and open loop. Open loop mode uses an air measuring device to determine fuel requriements, with a baseline timing table, an oxygen sensor to continually adjust AFR to 14.7:1 (or close to it). The ECU does NOT increase timing, to the point of knock, then dial it back a notch. It can ONLY retard timing (this is why they use KNOCK sensors... only able to sense detonation). Open loop mode is used continuously in all conditions, with the one exception of WOT.
Closed loop mode is reserved for only WOT. In this senario, the engine operates off it's pre-determined fuel/ignition table, and completely ignores knock sensors. This is how it's possible to damage your engine with aftermarket programming tools... 
There are only a handfull vehicles today that contain a 'learning' ecu, that continually adjusts engine performance to octane requirements. They do not use Knock sensors at all, but employ a computer system that actually measures itself while it drives down the road.
I am not a VW engineer, and cannot make any claims as to the abiltiies of the Phaeton ECU. Although, I see no reason why the Phaeton (or Bently, or Audi A8) would require such a system.
Some other random thoughts from reading this thread...
Oxygenated fuels's octane rating is sufficient. Although, there is less energy in an oxygenated fuel. Meaning, your fuel mileage will decrease a bit.
I'm told, that years ago only premium fuel contained all the additives that were good for your engine. Today, all grades contain the same additives.
Fuel from every gas station carring the same octane is exctly the same. It is refined at a central location, and distributed to local fueling stations. BP = Arco = Shell. You can even watch the fuel truck stop at different stations on the way.
Fuel attatives found at your local auto parts store, do not significantly change the composition of a normal tank of fuel, and therfore, will not provide any benefit (except lightening your wallet).
Jason


----------



## kc drifto (Jul 7, 2008)

*Re: Shell V-Power 99 RON Petrol (NorCalJason)*

that's allot of info norcal jason...i agree except that the only time the knock sensors get "ignored" is only when the engine is <70 degrees f. my cars have a potentiometer in place of the sensor for on the dash air fuel ratio adjustment http://****************.com/smile/emthup.gif


----------



## PanEuropean (Nov 3, 2001)

Photos and PDF re-hosted.

Michael


----------

