[maciek2000]

I really dont know. It is for sure related with chain. Can anybody help me ?

[XIXTRUMP]

Octane rating is a scale that indicates the anti-knocking capacity of fuels, based on the comparison between the iso octane knocking capacity mixed with heptane. High octane number indicates a low tendency  of an hydrocarbon to explode (knock) in an engine system.

It was demonstrated that chain ramifications raises the octane rating. Functional groups involving oxigen, such as alcohols and in this case an ether, raises the octane rating too.