Conversation so far:
why is mtbe used as a gasoline additive
Methyl tert-butyl ether (MTBE) is a blending component of gasoline, used as an oxygenate to raise the octane number and to replace tetraethyllead (TEL).

Question: what is the benefit of rasing the octane number
Self-contained rewrite: what is the benefit of raising the octane number in gasoline