If your real Quadra 800 has a dead ROM (usually due to a failed trace or internal chip death), you must burn a new one.
Early Quadra 800 ROMs shipped with a 24-bit memory addressing compatibility mode that cripples modern RAM expansions. A custom ROM patch (like the "32-bit clean" mod) forces the system into full 32-bit mode, allowing you to max out the board at 256MB of RAM. quadra800rom work
Apply overclocking patches to help the machine run stable at higher clock speeds. The Definitive Guide to Quadra800ROM Work: Emulation, Dumps,