So I was talking to a BMW master tech the other day in regards to my Z4M and how it runs on California 91 octane gas. He was telling me that not even the 93 or 94 octane available elsewhere in the country are sufficient to exact the full performance the car is capable of and tuned for from the factory. He suggested the ideal octane would be 100, stating that anything higher would no longer be beneficial. Seeing as the gt3 has a similar but even higher compression engine, what do you guys think would hypothetically be the ideal octane to run once I take delivery of my mkII?

 

my RS has Revo software with two ECU settings, 1 for 91 and another for 100. And the 100 is noticeable stronger. I suspect you will need software like Revo or GIAC to extract maximum benefit from higher octanes (vs. no software).

 

If your car is stock, 91 is good enough. You will only benefit from higher octane if your tune is on the edge or close to the edge of blowing up.

 

My ECU was flashed for and set for 93 octane. I recently did a track event where I mixed 93 and 100 at a 50/50 rate. The car definitely ran stronger with the mix, which should have averaged out to 96 or 97 octane. For the last run of the day, I needed to refuel again, so I just put in 93 thinking I would run the rest of the tank out on the street, and there was a noticeable performance decrease with straight 93.

 

Your "seat of the pants" feel is not from the higher octane, it's most likely from the different tune, or you simply just drove better when you mixed the 100. There is always a notion that a car performs better when using higher octane fuel, but it's all psychological. Octane doesn't add HP, it just gives you more cushion from detonation, so you can tune the car leaner which will yield to more power. If you dyno a car without changing the tune, just with different fuel, I would bet you won't see any performance gain. You do run "safer" with a higher octane fuel though.