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Originally Posted by BCT748  That's true for older motors. Newer ones will retard the timing if it starts to knock. |
I still haven't come across many knock sensors on motorcycles yet... : )
That said, I stand by my assertion that newer motors are designed to do more on lower octane. You can't go by the old 10:1 == high test rule any more, it's not that simple.
For example, I've got one motor with 300+ PSI of dynamic compression, I dunno how much more 'cause I haven't found a compression tester that reads high enough. Static compression is around 13.5 to 14:1, gotta recheck since I went to thinner gaskets. It runs all day long, whipped and abused on 89 octane. It's air cooled to boot. Ignition is running 3 deg advanced from factory.
Flatter valve angles, better understandings of combustion chamber shapes, piston dome shapes, and their interactions together are resulting in much more detonation preventing setups. (A good example is the Honda V4 series in the mid 80s, a big part of the design effort for the heads was coming up with something that would allow higher compression while being able to run on 87 octane.)
For the most part, unless you're running a BUILT motor in your bike, it'll likely be quite happy with midgrade or even low test. It's easy enough to drop from Premium to mid grade and see if it gives warning pings. If it doesn't, when the tank is half empty, fill it with low test and see what it does. No pings, feed it straight low test, etc.