Maybe it was that one?

 

Yes - just posted in his new thread.

 

Spain is a beautiful country but it doesn't have it's own set of physics laws.
He demonstrated his misunderstanding of how engines operate when he refered to the engine in the STR as low compression as if that fact alone was enough to make an eligible candidate for low octane gas. Someone might read that and think he's correct. He is not.

You're doing that same thing by not understanding that this engine will adjust for lower octane and you probably never will hear a ping.

 

It's an assertion that it will adjust for lower octane. Hopefully it will, but I've never seen any evidence that the PCMs (they vary) in the STR actually do that for gas below the specified octane range. The PCMs are VERY busy in these cars so they may not.

 

That's what I've told by Jag service managers but I'll bring this topic up at next weekend's Jag club picnic. It's quite likely that someone from the technical department of Jaguar North American will be there so I'll ask. They should be able to find out if they don't know outright.

 

Jorge,

You made some valid points, especially with the misguided assumption that higher priced premium gas means higher quality gas, but are off the mark when it comes to comparing the compression ratios of the R with non-R. The 9:1 spec of the R is without benefit of the boost provided by the supercharger. The actual C/R with the engine running and 'on the boost' is equal to or higher than the non-R.

I liked your comparison to filling swimming pools with mineral water- many people do treat their cars that way with overpriced boutique oils, additives, filters etc etc. The cars don't benefit in any way, but the owner feels much better.

 

It seems then that I was wrong with the compression, as pointed to the "piston" compresion we have to add the already compressed air so the total compression is higher I guess.

In any case Jaguar recommends RON95 for the STR and in Spain that means "standard" petrol so I put that. On my Porsche 964 it says RON95 so I feed her with that and I only put RON98 (premium in Spain) when I go to a trackday... just in case it gives a little more, but in fact I don't know if it does.

This thread is very long and so far my conclusion is that in Spain I can put "standard" but if I take my STR to the US I'll have to put premium.

By the way "standard" petrol in Spain cost 1.32€ per litre which is about 1.82USD per litre or aproximately 6.89USD per US galon. How much is your "premium" there?

It might be that, accounting for cost only, my standard is like "super-premium" in the US.

Thank you for your help, I'll continue with RON95

 

Let`s just close this up. You want to run regular in an R? Do it. It won`t be good for it and likely will cause problems in the future. No need to debate a rather useless argument. Do it or not, it`s your car. Geez.

 

Good idea...

Wait, this statement isn't closing anything up, in fact it's "fueling" (pun intended) the debate...

 

We can't possibly close the thread until I speak with Jaguar tech on Saturday ...

Besides I think I may have finally invented the perpetual motion thread ...

 

By Roland Jones Business news editor msnbc.com

updated 7/23/2008 1:25:25 PM ET

With gasoline prices hitting record highs almost daily, you might be wondering if you can get away with filling up your expensive car with regular instead of the expensive premium gas your manufacturer recommends.


The answer: Regular’s fine in most cases, but it’s best to check your owner’s manual.
Given the high cost of a fill-up these days, Americans in almost every income bracket are cutting back, and those who drive high-end vehicles that demand premium gas are paying a higher price.


“In the vast majority of cars out there you can get away with using regular gas instead of premium, but there are a few hot rods like the Dodge Viper that require you to use it all the time,” says John Nielsen, director of the AAA’s Approved Auto Repair and Auto Buying Network.


“If it’s required, you’re often going to see that word in the owner’s manual, and that’s going to be very clear, but if it says premium is ‘recommended’ you can probably use something less expensive without any damage. So the best advice we can give to drivers is to check if their car requires premium gas by looking in their owner’s manual,” he said.


There are three basic provisos for gasoline usage in owner’s manuals: when only regular gas is required, when premium is “recommended” and when premium gas is “required.” Only in the third instance will deviating from the manufacturer’s requirements potentially harm your car, said David Champion, director of automobile testing at Consumer Reports.


Using premium gas in a car that only requires regular won’t help performance. As for cars for which premium gas is recommended, but not required — such as the V6 Nissan Maxima, the Toyota Camry V6 and Nissan Murano — using a higher-grade gas like premium will give you better engine performance, but not significantly better mileage, Champion said.


But if premium gas is required, those cars are designed to run only on premium and could possibly be damaged if you use regular over a prolonged period, Champion said. Cars that require premium gas are typically made by luxury brands like BMW, Mercedes, Lexus, VW and Audi, and some Acuras are also on that list, he said.
Video: A gadget that saves gas

At certain temperatures and altitudes, you might want to use premium because there could be some ‘pinging’ or engine ‘knock’ and there will be a slight loss performance, and the impact on the engine can sometimes be significant, he added. “So if premium is required, you could try using regular, and if [the engine] starts to ping use premium.”
Premium gas’ name is in some ways misleading. Premium doesn’t mean higher quality, it means higher octane, a term that measures how quickly a fuel burns (the higher the octane, the slower the burn).


A fuel’s burn rate used to matter because it controls the amount of engine “knock” or “pinging,” which refers to premature ignition of the fuel-air mixture inside the engine’s cylinders (it makes a sound similar to marbles inside an empty can). Occasional knocking is fine, but prolonged knocking can seriously damage an engine, according to AAA’s Web site, and so higher-octane, slower-burning gas is recommended to control it, especially in older cars.


But if you use regular gas in a modern car that requires premium, the potential for engine damage is somewhat limited because most of them now have a device that can sense engine “knocking” and can compensate for it to prevent any damage by automatically adjusting the car’s settings to a lower-octane gas.



Mid-grade gas is cheaper than premium, but it isn’t worth bothering with, said Champion. Regular gas has an octane level of 87, while mid-grade usually has an octane level of 89 and that is not sufficient for cars that require premium gas, which generally has an octane level of 91.


In the end, lowering the octane level of your gas will offer a modest saving. While the precise price difference between regular and premium gas changes depending on market conditions, AAA calculates that the current price spread between self-service regular and self-service premium is approximately 40 cents per gallon on a nationwide average basis.


So with regular gas at about $4 a gallon, that’s a saving of 9.5 percent of your fuel bill each time you visit the gas pump, said Jeff Sundstrom, AAA’s fuel price analyst.
Far more important than using regular or premium is the type of gas you put in your car, Sundstrom added. AAA advises using a major brand of gas that includes a detergent like Chevron’s Techron, he said. Detergents keep engine valves and fuel injectors free from the build-up of carbon deposits that can reduce an engine’s performance.


Another effective way to save on gas is to drive like your grandmother, said Champion. That means gentle acceleration, gradual braking and avoiding hard stops, he said. Accelerating too quickly can mean you have to brake harder and that can waste gas.
“Drive like your grandmother and your gas mileage will go up noticeably,” he said. “No changes you make at the pump can do that for you.”

 

Ooops. Argument against:

As long as it's clean
Profit is meaningless to the modern engine, which, regardless of what's specified in the owner's manual, hardly cares what you use — as long as it's clean.
Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used.



Extreme pressure inside the cylinders causes knock, which is the sound of the pistons literally rattling inside the cylinders. Too much too long can damage the engine. A little now and then won't.



The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.



Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.


Automakers say they don't test premium engines on regular to check the difference, but some auto engineers estimate that power declines roughly 5%.
"We can't guarantee the vehicle will perform as specified if other than premium fuel is used," says Mercedes-Benz spokeswoman Michelle Murad. All U.S. Mercedes engines specify premium.



All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.


Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.
High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine. No data show that engines designed strictly for regular run better or longer on premium.



The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."


There is "no way of taking advantage of premium in a regular-grade car," says Furey.
"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.

 

I do believe octane improvers are available as additives to petrol from accessory stores.
The forbidden tetra-ethyl-lead is not the only additive there is to slow combustion. I did some experiments in the 1970s with iodine. It cured knock-ping in a fleet of 1100 cc. Ford Escort estate cars. Try Google.
Whether or not you notice any difference in such a powerful car is a moot point of course.
Leedsman.

 

I think that by posting articles either for or against high octane fuel, (especially ones that contain inaccuracies) this just fans the flames of the debate, not acts to close it out.

 

If you can get a tech who works in the computer part of Jaguar to let us know (and for each of the PCMs), that would be useful. Realistically no-one else is likely to know for sure, though they may have an opinion.

The idea of putting a fuel out of the stated specification into a performance car does strike me as crazy, whatever the answer as to what the PCMs will do.

 

I thought about this long and hard. The AJ27 S/C comes with a lower CR than the NA 10.75:1 CR. In addition- at low load- which is in traffic and lower speeds the M112 supercharger is running on bypass and running no boost (this addresses the false claim that the engine is always running boost- at part load not only is it throttled but the SC is bypassed) and considered that it may be possible to run low octane. Then a flash of memory came back from 12 years ago and my Whitley development days in Coventry.I made a long distance call to an old friend/mentor from my Jag development days. I seem to recall some cars coming back from South Africa with badly nibbled pistons.
The knock sensing has a limit and beyond a certain point will no longer retard anymore.
It IS true, knock is far worse at Full load conditions but the S/C Jag engines are knock limited at some points at loads/BMEPs as low as 3 bar! Add to that that under the conditions where it is knock limited and running on 87 octane- the engine will be running alot less efficiently. After considering all of this I decided to continue running 93 octane

 

Aha. Looks like the answer - thanks!

 

So he decided to continue with 93 octane... but is that 93AKI or 93RON?

In any case my manual recommends 95RON which is what I put

Thanks,

Jorge.
(By the way, and here comes the misleading, 95RON y "regular" in Spain so I'm not putting "premium" but that is only a relative and misleading word, we should stop using the words "regular" and "premium" and use only what is really important the octane number using RON or AKI)

 

Jorge911 raises a point: We should not confuse compression ratio with "compression pressure". With a naturally aspirated petrol engine there's a direct link between the two, the wider the throttle opening the higher the compression pressure. The "ratio" is fixed by engine geometry. As soon as you force air into the engine with a super or turbocharger, the compression pressure rises, making knock-ping more likely.
This whole problem came to a real head with the RollsRoyce "Merlin" engine in the WW2 Spitfire, producing 2500horse with a compression ratio of over 12:1. I do believe combustion cooling and therefore slowing was achieved by water injection in that case. The petrol was also very high octane, as some RAF car drivers found out when they "acquired" it and put it in their cars causing damage. Petrol was strictly rationed then.
Suffice it to say, car makers have worked it all out as far as is humanly possible, the knock-ping problem being nothing new to them. Hence all the focus on stratified-charge petrol engines lately.
Leedsman.

 

With where he lives it will be 93 AKI I think, whereas only 91 is needed (for the S-Type R) I understand. 93 is likely harmless but I suspect also pointless. (Oh what have I said......)

edit: added (for the S-Type R) - the relevant poster (Count I) has an XJR