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ATI Radeon HD 3870 Extreme Overclocking: Results

After the BIOS update to solve the 862MHz problem, the described hardware modification enabled us to adjust the GPU and memory voltages in a wide range. The cooler’s fan was set at its maximum speed by means of RivaTuner to keep the GPU temperature within reasonable limits. Our attempt to overclock the GPU produced the following results:

  • 900MHz (891MHz according to RivaTuner) at 1.44V
  • 950MHz (945MHz according to RivaTuner) at 1.51V
  • 975MHz (972MHz according to RivaTuner) at 1.55V
  • 1000MHz (999MHz according to RivaTuner) at 1.71V

Obviously, we’ve got not the best sample of the ATI Radeon HD 3870. We only achieved a frequency of 1GHz at a voltage of 1.71V although other cards were reported to be stable at that frequency with 1.55-1.6V voltage. We could not lift the frequency to 1.1GHz at 1.75-1.77V and we didn’t increase the voltage further because 1.7V was already dangerous for the 55nm chip with a default voltage of 1.33V. The temperature showings were indicative of that: the fan working at the max speed, the GPU was as hot as 69-72°C when idle and over 90°C hot under load. We wouldn’t recommend you to repeat our experiment because there is a risk of damaging the card even if you provide enough cooling. Well, ordinary users do not use this kind of overclocking whereas true enthusiasts can’t be stopped by any warnings.

We managed to overclock the memory chips to 1242 (2484) MHz at a voltage of 2.05V. This increased the memory bandwidth from 72 to 79.5GBps. That’s not much. Anyway, that’s not the memory bandwidth that is going to be the main factor in games.

The card successfully passed a couple of test cycles in 3DMark06 and 3DMark Vantage at 999/2484MHz but would hang up in games after a while. We achieved perfect stability at 972MHz GPU and 1224 (2448) MHz memory frequencies. The card passed all of our tests successfully at these clock rates.

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