Premium or Regular Gas ?

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I never said it was a bad thing. Great cars. Considering one for my teenagers first car, since it is AWD. People are reading things into my posts that weren't there.
My only point was that it isn't an XK8 and the performance difference of regular vs. premium would be really trivial in this car.
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Hi Richard,
My comments were aimed at the larger audience rather than you.
I think that if the engine internals (compression ratio, computer software etc.) are indeed the same, you are correct.
However, I believe that the only engine block is shared (in the 3.0 liter 227 hp engine) and the x-type has jaguar high compression heads, ignition, fuel system and computer management. The engine (my understanding) is built by ford on a separate assembly line. This may account for the discrepancy?
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Been away....
DAS
For direct contact replace nospam with schmetterling
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I love it when dead threads are revived Double Tap
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What's the engine's compression ratio? If 10:1 or higher I'd used Premium, perhaps cheat a bit with mid grade in cool weather, but not hot weather. Higher ambient temperatures bring an engine that much closer to pinging so premium is needed then to prevent that pre-ignition.
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It's 10.5:1, so on the borderline. 227hp out of 3 liters.
You could safely run either. "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote in message

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US Premium gas is about on par with Euroland/UK regular unleaded. Or in other words your regular wouldn't pass the UK/Euroland acceptance test (not gov). However having said that you will find that the engine control system ECU will compensate for any type of crap fuel that will actually allow the engine to run but the quality of the gas does play a part in the power output and as I said the US lower quality gas is rather low quality and your high grade is about the same as our cheaper grade. Anyway, you pays your money and takes your choice.
Why didn't you buy a BMW?
Sir Hugh of Bognor
The difference between men and boys is the price of their toys. Intelligence is not knowing the answer but knowing where and how to find it!
Hugh Gundersen snipped-for-privacy@h-gee.co.uk Bognor Regis, W.Sussex, England, UK
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wrote:

Hugh, U.S. premium is 93 (R+M)/2 octane which = 98 RON.
So your UK/Euro premium is better than 98 RON? Or are you confusing sea level U.S. 93 premium with the U.S. 89~91 used in high altitude areas?
Tom K.
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wrote:

He'll get right back to you on that, once he finds someone who actually knows the answer ;-)
/daytripper '00 s4 6spd
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wrote:

Compliments of Wikipedia, he seems to have it backwards:
http://en.wikipedia.org/wiki/Gasoline
"Different countries have some variation in what RON (Research Octane Number) is standard for gasoline, or petrol. In the UK, ordinary regular unleaded petrol is 91 RON (not commonly available), premium unleaded petrol is always 95 RON, and super unleaded is usually 97-98 RON. However both Shell and BP produce fuel at 102 RON for cars with hi-performance engines, and the supermarket chain Tesco began in 2006 to sell super unleaded petrol rated at 99 RON. In the US, octane ratings in fuels can vary between 86-87 AKI (91-92 RON) for regular, through 89-90 (94-95) for mid-grade (European Premium), up to 90-94 (RON 95-99) for premium unleaded or E10 (Super in Europe)"
Our regular is 89, so 94-95 RON. UK regular is 91 RON. 87 can be found at bargain places, but not easily, at least where I live.
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wrote:

Bognor Regis, W.Sussex, England, UK
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The computer can retard the timing to deal with the lower grade of fuel. Having said that, it is not possible to retard the timing AND retain the performance. There must be a trade off. Is the trade off noticable to him, or you? Maybe not, and therefore regular fuel should be okay. But, there is certainly something lost by retarding the ignition timing.
Personally, I would run a minimum of 3 full tanks of gas doing your normal kind of driving, and 5 tanks is better. Average the consumption then switch to the other grade of fuel and run the test again. I suspect that premium fuel will indeed give better mileage. Divide the fuel cost by the mileage yielded to arrive at the cost per mile. You may find that the cost per mile is actually lower with the expensive grade of fuel. In my area, premium fuel typically costs $0.20 more than regular, so if regular costs 2.30, then premium will cost 2.50. If the mileage is 22 on regular and 25 on premium, then regular costs 0.1045 per mile, but premium costs $0.1000. Premium is cheaper in this example. In 10,000 miles, you'll save $45, and have a bit more pep.
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Jeff,
I have been following the thread since my original post. I like your suggestion and will try it.
Double Tap
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I have not followed up on all of the posts, but I did reply to your initial post.
I happen to run 89 in my '94 BMW 3 Series. My daughter also runs 89 in her '00 BMW 3 Series. We are both happy with the performance and economy trade offs, and the cars don't seem to mind.
I have not run the mileage tests that I described, but there is no reason to believe they will not give the results -- except that the actual numbers may vary -- I talked about. The idea being that once you establish the benchmarks, you can then make the decisions you are asking us about. Without the benchmarks, the gas you buy is more or less a crap shoot.
I elected to simply use the mid grade in my cars. If I go to Costco for gas, they only sell regular and premium, then I get the premium, but at the station down on the corner, I get the mid-grade.
Cars that only require regular derive NO BENEFIT from premium, but a car that needs premium will run better and more efficiently on premium than it will when it is fed regular. A car wants premium will run okay on regular, better on mid grade, and best on high test.
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(snip)
I agree with your logic and plan to test 87 PON mileage against the 93 I normally burn in my E46 - as soon we no longer have the "reformulated" winter gas. But I'm not really tempted by 89 PON as it's 10 cents more than 87, but 93 is only 10 cents more than 89 (in my area). In other words, by the pricing, "mid-grade" should be 90, not 89. Also, a new phenomena is "off brand" stations charging a differential of only 12 or 13 cents between 87 and 93, making the 93 even more of a bargain.
The manual for my BMW R1200RT motorcycle (12:1 compression) actually states that rated hp drops from 110 to 101 when the knock sensor retards the timing because of lower octane.
Wouldn't it be nice if EPA mileage figures specified the test octane on those cars which call for above regular grades?
Tom K.
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What a great and informative discussion of this critically important issue!
My two bits worth:
Re: using lower grade fuels. I found the following in an article on the Internet, for what it is worth:
"... there are fuel refineries across the country that will occasionally blend in bigger percentages of the inexpensive and very plentiful alcohol. It is said that some of these blends can contain as much as 15 to 20 % alcohol. Is this legal? ... probably not. However in a world of discount gas stations located in outlying areas, a don't ask don't tell policy is in place when the price is right. If an unknowing motorist buys a load of 15% - 20% alcohol fuel, his car starts a little harder and runs a little lazier. How can you know the true content? ... you can't. This underlines the need to buy fuel at a name brand retailer, or a station that you are familiar with.
"Another complication of alcohol is the high solvency. That is, it has a lesser lubricicity than the fuel it is being blended with. This higher solvency literally washes internal engine surfaces that require a presence of lubrication.
"The last significant complication with alcohol is that it attracts water. That is to say that it literally draws water out of the surrounding atmosphere into the fuel. This drawn-in water then enters the engine along with the fuel and oil. While the percentage of water content is low, it further contributes to the internal "washing" of surfaces needing lubrication. Blends that contain more alcohol can attract more water."
A final note: I use Chevron 94 Octane (the highest rating available in Canada) in my 2001 VDP. Chevron contains Techron, which has been formulated to remove potentially harmful deposits from injectors, intake valves, and combustion chambers. Currently it costs $1.11 a litre -- about 10 cents a litre more than 91 Octane and about 12 cents a litre more than 87 Octane.
Alan Strickland Victoria BC Canada

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Why not? They call blends like this ethanol.
However in a world of discount gas

They don't sell ethanol in my area, but I _thought_ they had to clearly indicate that they were selling ethanol if that was what they are selling.
This underlines the need

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You might want to check the recent state law changes in your area. In my state, Maryland, ethanol is now virtually mandated (see link )and has replaced MTBE for the "reformulated" gas we get from November to March. From what I can tell, my mileage is a bit worse and the pumps are not so labeled!
http://www.mde.state.md.us/ResearchCenter/Publications/General/eMDE/vol2no4/alternativefuels.asp
Tom K.
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wrote:

Bognor Regis, W.Sussex, England, UK
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I have no doubt that the grade or octane level is not as constant as we all might think. Anyway, mixing alcohol to stretch the gasoline dollar is not the final answer to any energy discussion. Why? Because you'll use more gallons or litres.
What a great idea! We'll mix cheap alcohol with expensive gasoline. Too bad the end product has less than 90% of the calorific value of plain old gasoline, meaning that to achieve an equal amount of energy you'll have to burn more of it. People will spend just as much and in many cases more money than before.

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