What octane really required?

[clickman]

This question got buried by all the flaming going on in the original thread, so I'll try again:

So I'm trying to understand what octane rating I really need here in the great white north:

My manual says:

1. "Your engine is designed to provide optimum performance and fuel economy using unleaded premiuim fuel with an octane rating of 98 RON (93 CLC or AKI).

Porsche also recognizes that these fuels may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI), since the engine's "Electronic Oktane knock control" will adapt the ignition timing, if necessary."

2. On the fuel filler door of my Box it says "Minimum octane RON+MON/2 = 93"

Some quick net research tells me that AKI (Anti Knock Index) is the same as (R+M)/2.

Therefore the manual and the fuel filler door don't agree, and I'm left wondering if I really can run 91 or 92 instead of the much pricier and rarer 94 I'm currently using.

It sounds some of you are running 91 without any issues, but I'd like to know if that's more universally the case before I switch.

And I'm also curious if USA cars have the same label on the fuel filler door that I have.

[TriGem2k]

Here in California you will be hard pressed to find anything above 91 Octane.

Personally if we had 92 93 or 94 Octane here I would use the highest possible. If what I know is correct our engines were tested with 93 Octane.

You also have to consider the fact that just because the pump says 94 Octane you could very well only be getting 92 or maybe you're getting 95. It all depends on the process in which that particular batch of fuel was made.

If you’re not worried about saving a pretty penny then stick with 94. If you’re looking to save a buck or two every fill up by all means use a lower octane but I don't think anyone would recommend that you do.

~James

[LowFlyR]

I have not found 93oct here anywhere, but I have found some stations with 100oct racing gas. So I'm wondering if this thought of mine daes make any sense:
How to get 93 oct with 91 & 100 oct.
available:(gal x oct + gal x oct) / tankfull gal = average
First tank(4*100+12*91)/16=93.25
next tanks(3*100+10*91+3*93.25)/16=93.11

So, first time put in 4gal of 100oct and the rest 91oct (if your tank is 16gal total) from then on you only have to fill 3gal of 100oct, because you have a leftover 3gals of 93.25oct. Does this make ANY sense???

[r9i8c7k]

Just use the highest octane you can find and call it a day.

[porsche986spyder]

My Chevron (Texas) always carries 93 Octane. I'm not sure about the ones up North.

[LowFlyR]

Originally Posted by r9i8c7k

Just use the highest octane you can find and call it a day.

I wish. 100oct is $4.99 / gal

[racer_d]

Originally Posted by clickman

My manual says:

1. "Your engine is designed to provide optimum performance and fuel economy using unleaded premiuim fuel with an octane rating of 98 RON (93 CLC or AKI).

Porsche also recognizes that these fuels may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI), since the engine's "Electronic Oktane knock control" will adapt the ignition timing, if necessary."

2. On the fuel filler door of my Box it says "Minimum octane RON+MON/2 = 93"

Some quick net research tells me that AKI (Anti Knock Index) is the same as (R+M)/2.

Therefore the manual and the fuel filler door don't agree, and I'm left wondering if I really can run 91 or 92 instead of the much pricier and rarer 94 I'm currently using.

It sounds some of you are running 91 without any issues, but I'd like to know if that's more universally the case before I switch.
.

To me the manual and filler door say the same - see bold. The manual then states you won't necessarily harm the motor with only 91 octane. It simply will play with the ignition, an potentially reduce power, so as to limit any detonation.

[Darkhamr]

The manual and the filler door are the same.
In many places 91 is the highest and many people are using it without issues. You may see a reduction in performance with 91, but it would be hard to test and statistically prove a performance difference with 93 over 91 for the consumer. If cost was an issue I would spend the extra for the 94 during the hot summer months and 91 or above the other 9 months when it's cooler out and less chance of knocking.