Assalamualaikum Brother. I have no personal experience in Suzuki Alto or Toyota Corolla Altis 2010 1.8VVti, but i know that maybe the manual PKDM 1.8 with 1ZZFE, that you mentioned may touch 8km/l or max 10km/l in the city. Meanwhile the newer 2011 - 2014 Corolla Altis facelift with 1ZRFE in Manual may touch 9km/l to 11km/l. All these are assumptions above. None of this justifies the 1.8 newer manual or CVTi Corolla Altis 1.8 touching anywhere above 12km/l or above in normal conditions even with hi octane inside the city or urban traffic. None the less your car, your rules. Maybe you have long drives and have no traffic or signals in your daily route. Still 18km/l in the city, is out of this world. Peace Out.