Delcrossv is correct. I've extensively experimented with the timing through out the RPM range and E90-E98 likes pretty much what non-oxgenated gas based fuels like. You "might" gain a tad from adding 1-3 degrees, but it's not much. You gain much more from the added compression. On this build, I would start with a few degrees less. My really high compression (17:1 static) Busa engine, at peak torque, actually likes 2 degrees less than the stock timing curve when on E98.
