the Walnut Diary

My Porsche Cayenne S has a label on its fuel filler door which sternly warns that this engine requires 98 RON fuel. I have felt guilty giving Ruby 91 octane, but it’s the hottest gasoline I can find in my area.

Then this week on the outskirts of Kingston I saw 94 octane as a choice on my pump. $1.459 per litre was quite a premium over 1.139 for regular and about 1.269 for premium. Nonetheless I decided to try a tank of super-premium and rake in the performance and fuel mileage benefits.

At low speeds Ruby accelerates a bit more strongly with the hotter fuel, and I notice the gear changes aren’t quite as smooth, as if the engine produces more torque. I didn’t notice any difference in performance at highway speeds, though. The Cayenne is pretty strong in the passing lane with its usual premium fuel, in any case.

The surprise was Ruby seems to use a bit more fuel than with 91. I’ll update this when I have more data, but my impression is that fuel consumption is up 1 to 2%.

Wikipedia informed me that the German RON 98 is the equivalent of the North American AKI 91-92, so I wasn’t actually starving Ruby. With the hefty cost increase for super-premium, I can’t see the point of the richer fuel in a Porsche V8.

Tom Stutzman sent along this link:

American vs European fuels – Octane rating

UPDATE: 1 March, 2018

After a couple of drives on two laner’s in light traffic, I have decided that Ruby’s sparkling performance in the passing lane is rather good. Next fill-up if 94 is available I may try another tank, just to be sure it’s a waste of money.

UPDATE:  7 December, 2018

In my reading about O2 sensor failure, I ran across a couple of Cayenne S owners, one in BC and one in Ontario,  who tied their O2 sensor failures to American high test gasoline.  They suspected the ethanol in U.S. 91 octane.  I was not aware that only in Canada do they keep 91 ethanol-free.