Jim (CIA PCA region)

John, I believe that 98 number is via European measure. With the US (RON+ROM/2) measure, they are recommending 93 only, which you may or may not be able to find, depending on location. I have only two stations with 93 Octane VPower left in my area, the rest have 10% Ethanol. BP recently downgraded their "Ultimate" fuel to 91 -- no decrease in price, unfortunately.

Last autumn I did the PCA Treffen (highly recommended, BTW), and the PAG employees filled the cars with VPower exclusively (southern Germany, at about $6.90/U.S. gallon) and it was labeled '100 Oktan', which if we could get in the U.S., would be 95 octane by our measure. PM if you want to see a photo of the pump.

In England one can buy 'BP Ultimate 102', which is 102 by their measure, and 96 by ours, plus it meets FIA F1 specs. I think Shell's competing fuel is Optimax.

HTH,

Jim

John Boggiano

OK, guys. Thanks for all the info.

So the Euro (RON) rating works out at 5 to 6 points higher than the equivalent Octane (USA) rating. And Porsche still recommends 98RON or 93 Octane wherever the car is marketed. But it seems some people have no option but to use lower grades.

I guess I'll only do so if and when it becomes absolutely necessary and then be gentle with it.

Just as a final confirmation, could someone in CA (and therfore running 91 Octane) please confirm for me that the fuel flap still states '93'?

Jim (CIA PCA region)

Well my car isn't a California car, but the flap says Recommended 93 (RON+ROM/2), Minimum 91 (RON+ROM/2). I believe California is the same, but can't say for sure.

John Boggiano

Thanks, Jim.

Suggests to me that there may be some difference in the ECU or elsewhere to allow for the lower grade in ceratin markets, as the Euro cars (well mine, at least) simply state '98 RON'.

dasams

If I were responsible for US applications of the ECU, I'd design for 93 (RON + MON)/2 so those fortunate enough to get it aren't penalized. I'd also design the ECU to retard the ignition as necessary for 92 and 91 gasolines. In other words, a single ECU for all US gasolines (which is what we have).

Perhaps the flap doesn't have a (RON+MON)/2 rating simply because it isn't reported that way in the UK. What info is given on the pump?

Jim (CIA PCA region)

D'oh! I meant RON+MON/2.

Jim (CIA PCA region)

While the plural of anecdotes isn't data, I read a post once where the person had talked to some engineering types at the 997 launch, IIRC, and they said the GT3 and 997S engines on 93 isn't an optimal combination, they really would like more octane (I note they use the equivalent of 95 in Germany). So it's multi-hand information, but it sounds plausible. I suspect using 91 is a notable performance hit.

Jim

aperalta

In southern cal you can actually get 100 octane unleaded. For my 96tt I put 5 gallons of 100 and the rest 91.

silverboy

Can octane boosters help for those days you want to push the car hard?

Max Power

in Pennsylvania, a few Sunoco stations have GT100. $8.19/gallon. Almost as expensive as gas in Europe

most Sunocos here only carry 93 octane though

you could put 5 gallons of GT100 in and then top off with 93.

http://www.sunocoinc.com/site/Consum...T100Locations/

Nordschleife

D'oh you meant

(Ron+MON)/2

John Boggiano

OK, guys, this has been an extremely informative discussion, but it's time for me to hang my head in shame.

Although I had 'read' the manual when I took delivery, it's only last night that I found the time (been too busy driving! ) to read it cover-to-cover. Buried inside on two separate occasions is the news I was seeking - my engine will run perfectly happily on 95RON, but (obviously) will only give optimal performance on 98RON. Now why couldn't Porsche just have given that option on the fuel flap and in the 'beginners start here' bits of the manual?

Still, I've ended up not only with the answer to my question, but a working knowledge of worldwide fuel grades and how they are calculated. Thanks, everyone.

Jim (CIA PCA region)

NoSubEDU

FWIW, I ran 100 octane (unleaded) in the 3 at VIR and the car seemed to pick up some torque and HP. Also purred like butter.

Jim (CIA PCA region)

Okay, here are two pumps, one in Bavaria last fall, the other here in the Midwestern U.S. as of last Saturday -- assuming I got them attached correctly. The Bavarian pump isn't marked as to method, so I'm guessing RON. The U.S. pump is (R+M)/2.