Methods and systems are provided for adjusting engine operation of a hybrid vehicle to increase power output and fuel efficiency. In one example, a method may include operating the engine using an Atkinson cycle during a lower than threshold engine torque demand and a lower than threshold battery state of charge, and operating the engine using an Otto cycle during a higher than threshold torque demand. During operation in the Otto cycle, an octane booster is injected to the fuel line to increase the octane level in the fuel, if desired.