The Centris series of Macs only included three models: the 20 MHz Centris 610, the 25 MHz Centris 650, and the Centris 660av, which is identical to the Quadra 660av. The 660av is covered on Overclocking the Quadra AV Models.
These pages provide information on the maximum reliable speed. This may vary from one machine to the next. Chipping is not authorized by Apple. Any modifications you perform on your Mac may damage your Mac. Modifications are done at your own risk.
Be sure to visit The Clock Chipping Home Page, the definitive resource on chipping the Mac.
The Centris 610 has a 20 MHz 680LC040, which is a 68040 without a built-in FPU. Simply replacing the CPU with a full ‘040 will improve performance. The 610 has a 10 MHz oscillator and the CPU runs internally at 20 MHz. You can install a 14.0 or 14.31818 MHz oscillator for speeds of 28 and 28.6 MHz while still supporting the built-in serial ports.
If you don’t need to use those serial ports, a 15 MHz oscillator will boost you to 30 MHz. If you have a PPC card and want to use the serial ports, top oscillator speed is 14.2857 MHz for a CPU speed of 28.5 MHz.
The Centris 650 has a 12.5 MHz oscillator which runs the processor internally at 25 MHz (twice oscillator speed). The maximum oscillator you can replace it with while keeping the serial ports functional is 14.7456 MHz, to run the processor at 29.4912 MHz, although 28 MHz from a 14 MHz oscillator is safer.
If you don’t need to use the serial ports, you can put in a 20 MHz oscillator, to run the processor at 40 MHz. If you perform the Centris 650 Serial Port Modification, you can make the computer run at much higher speeds. The maximum oscillator while keeping the serial ports functional will now be 20 MHz, to run the processor at 40 MHz. With an Apple PPC card installed, the maximum oscillator you can use is 19.44755 MHz, to run the 68040 at 38.8951 MHz, and the PPC card at 77.7902 MHz.
- Info from Machine Specifics