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Old May 13th, 2008, 08:52 AM   #1
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gas grade

Its more than likely a foregone conclusion, but is it must to use premium gas in a 2002 Boxster?
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Old May 14th, 2008, 11:51 AM   #2
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What's premium at your location? 91 or 93? Since you cannot get 93 everywhere, cars must be able to use 91. I don't know what the performance benefit might be. Some engines benefit from the higher octane. It also might have more additives.

I would not use 89.
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Old May 14th, 2008, 02:32 PM   #3
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gas grade

Thank you for your reply. Is not using 89 octane a question of performance or will using it or something inbetween premium and regular or regular more a question of doing damage to the engine? I have been using 91 and 93 when I can get it. I have owned the car for a little less than 6,000 miles and it has ran great so far. The question I ask is of course somewhat brought on by the rapidly rising gas prices, especially in WV.
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Old May 15th, 2008, 09:17 AM   #4
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The reason why the recommended gas in the Boxster is minimum 93 octane is because the car has a high compression ratio 11.3:1 IIRC.
Higher compression engines will prematurely detonate lower octane grades, causing pinging and knocking which can potentially damage the engine in the long-term.
The Boxster can compensate somewhat for the lower octanes, but you should use the highest octane you can find.
There is a minimal performance boost with the higher octanes. Try racing fuel one day (100+ octane) and you will see.
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Old May 17th, 2008, 10:15 AM   #5
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I use 91 premium (its what we have in the bay area) in my 02. No sense in risking your 10k engine to detonation to save 5c/gallon in gas

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Old May 18th, 2008, 08:06 AM   #6
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It is not as bad as you think

Actually if you do the math you will realize that the higher grade is not as expensive as you think

If there is a 20 cent difference between the 87 and 91 octane fuel and you are putting 15 gallons in you are only paying an extra $3.00.

Not too hard to stomach.
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Old May 19th, 2008, 03:21 PM   #7
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Octane rating is the ability of a the fuel to avoid pre-ignition. The higher the rating the more resistance. Engine compression - the higher the compression ratio the higher the likelihood of pre ignition. Engine timing is set to get the spark to fire prior to the cylinder hitting top dead center such that the complete explosion occurs at the optimum time (each engine is different). The pinging that happens with the lower Octane gas is because it preignited (as Pedro stated). This is bad for the engine because it puts extra stress and wear on the critical engine parts. Porsche recommends 93 Octane but says 91 is acceptable. I agree, do not go below this to 89. The Porsche engine has sensors determine if/when predetonation occurs and compensates accordingly. I do not know what technique Porsche uses, but most either increase the fuel mixture or change the ignition timing. This can only compensate so much. It also reduces the engine preformance because it is now in a non optimal setting. I think that Pedro has it reversed. 100 Octane does not increase performance. If you had a car that was made for low Octane (low compression) you would see no effect with 100. What you see is the degradation of performance in the Porsche as it compensates for the lower octane fuel that is available to us.
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Old May 19th, 2008, 03:34 PM   #8
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I ran 87 in my '99 all the time unless I was on the track or at an AX.
Car did not run any rougher with the lower grade gas and never pinged (detonated)
the very complex computer programs and detonation sensors will always just back off the timing a bit and the car runs just fine.

you may have a slightly decreased level of perfomance, but it won't hurt the motor. The computer won't let it.
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