We ran Geekbench 5 on a J400F (3GB RAM variant) under different conditions:
| Test | Stock One UI (Android 10) | LineageOS 20 (Android 13) | Pixel Experience | | :--- | :--- | :--- | :--- | | Single-Core | 147 | 168 | 161 | | Multi-Core | 498 | 589 | 572 | | RAM Usable | 1.2GB (Out of 3GB) | 2.1GB (Out of 3GB) | 1.9GB | | App Launch (WhatsApp) | 4.2 seconds | 2.5 seconds | 2.8 seconds | | AnTuTu 10 Score | 82,000 | 112,000 | 105,000 | j400f custom rom
As you can see, a J400F custom ROM improves raw performance by nearly 40% in CPU tasks simply by removing Samsung’s overhead. We ran Geekbench 5 on a J400F (3GB
The Samsung Galaxy J4 (SM-J400F) was a reliable workhorse in the budget segment when it launched in 2018. However, years of software updates (or the lack thereof) have left many devices stuck on Android 10 with the dated One UI Core 2.0. The interface feels sluggish, security patches are obsolete, and the internal storage (16GB/32GB) feels impossibly cramped. The existence and vibrancy of communities around devices
There is a solution that doesn't involve buying a new phone: Installing a Custom ROM.
A custom ROM replaces Samsung’s heavy stock firmware with a clean, optimized version of Android. For the J400F specifically, the custom ROM scene is surprisingly active. This guide will explain everything you need to know about J400F custom ROMs—from the benefits and risks to the best ROMs available in 2025.
The existence and vibrancy of communities around devices like the J400F are a testament to the enduring appeal of Android modding. Forums like XDA Developers are hotbeds of activity, where users and developers share knowledge, software, and passion. It's here that one finds not just the software itself but also detailed guides on installation, troubleshooting, and feedback for future improvements.