For those who want an absolute speed demon and don't mind staying on Android Lollipop (5.1), the unofficial CM 12.1 builds are legendarily fast on this device. The grandfather of LineageOS. Barebones and wicked fast. Why it’s top tier:
Often considered the gold standard, LineageOS 16 (based on Android 9.0 Pie) is the most stable option for the Y51L. It provides a clean, bloat-free experience that significantly speeds up the aging Snapdragon 410 chipset. vivo y51 custom rom top