Okay first off, 4-cylinder engines have better Power Delivery than 3-cylinder engines, this doesn't necessarily mean they are powerful, it just means they have better pick! This also doesn't mean that 4-cylinder Vitz is less powerful than 3-cylinder, I am debunking the myth that 4-cyl in general are more powerful. Second up, I think 1L Vitz engine has a compression ratio of 11 or 11.5. whereas 1.3L Vitz engine has a compression ratio of 10 or 10.5. The higher the compression ratio the more picky the engine is about fuel due to pre-detonation and knocking. Less power and fuel is used to maintain engine on idle for 3-cylinder engines due to less frictional losses and more fuel-efficiency. That is why 4-cylinder Vitz can run on local fuel whereas 3-cylinder Vitz requires higher octane numbers.