Once I enabled K-boost but after some time I deactivated it. But the effects of K-Boost does not turn off even after when I disabled it in Precision X. I have uninstalled Precision X and the re-installed it but the problem persists and K-Boost feature is still turned ON. Can someone help me tto fix this prob. because My GPU temperature exceeds 70 C while playing Assassin's Creed Revelation. But before, when the K-Boost feature was OFF, I played this game and temperature does not reach 69C Also by enabling this feature will the card downclock when it reachs 70 C? 

Try re-installing PrecisonX and when it prompts you if you want to keep your settings select "no" and it will do a clean install. Yes your cards will still downclock if they hit 70C. Honestly they really shouldn't get above 64-66c, my 670 FTWs run around 50-52C @1254mhz core/3707mhz memory, which is a pretty nice oc on top of the factory +85mhz. I would check out your fan curve, make sure it looks like mine- if your still unable to keep under 70C with adjustment to curve, you may want to check out your case/cooling solution/fans. 

Thnkx a lot SeanEJohan. Re-installing Precision X did not help. However I un-installed and then re-installed the NVIDIA Drivers of my GPU and that resolved my problem. You said that the card will still downclock if it hits 70C. I have heared it from different people as well. But a member of EVGA support team mailed me and said that
"This model has a thermal threshold of 97c, so if you are below 90c I wouldn't be concerned."
(We are talking about GTX 670 FTW+ 4GB)
Can you (or someone else) explain the contradiction please? Moreover, I have recently purchased it and I am new. So I'll highly appreciate if you guide me in detail how to overclock my GPU using Precision X to achieve max performance it can deliver. I don't care about fan noise but right now, I can't afford Water Cooling System.
 
Intel i7-2600 Sandy Bridge @ 3.4 GHz
Motherboard = Intel DH67CL
RAM = 16GB DDR3
GPU= EVGA GeForce GTX 670 FTW+ 4GB
PSU= GS Series GS800- 80 PLUS® Bronze Certified Power Supply “2013 Edition”
Chasis = Cooler Master Storm Enforcer
  

Well their are 2 heat thresholds to be aware of, 70C and the higher max tolerance of 97C(I personally think its 104C but we'll stick to what the Evga guy said). You really shouldn't freak out about the 70C temperature downclock, its minor -15mhz. Although it should be easy to stay under 70C with the proper fan curve, if you go over it, no big deal, you aren't doing any damage to the card if you running 75-80C, but you also won't get the best performance out of them running above 70C. 
With every card being unique in what it can handle overclock wise, I would start off with a +58mhz to the core clock, and the memory can easily handle +400(3500mhz). Max the voltage setting to 1.175(this is safe, the card can handle much higher voltage with a custom bios)If you temps are okay and your aren't seeing artifacts or driver failures then you can overclock more, this time go in increments of +25 to the core. My top card is stable at +135 or 1319mhz and memory is stable at +600 or 3707, but my bottom card only will go up to 1280mhz or +58, before becoming unstable(same memory setting +600/3707). Also always make your pwr target max of 145%.
Now K-boost is ideal for overclocking and getting the most out of your cards. Without it, you may not see your overclock come into play much, as your letting the boost program dictate when to use higher core frequencies in games.
I would add some points on your fan curve(just click on the area you want to add one) and make it similar to mine, and you should be way under the 70C threshold. The highest temp my cards will see is 64C with this curve. I also have tons of case fans which def attributes to the cards staying cool(dedicated gpu fan).
So try this- at 50C make your fan speed 55%/at 55C make it 60%/ at 60C make it 65%/ at 70C make it 72-75%/ and at 75C make it max of 80%.

I've been running K-boost for well over 9 months with clocks/voltage locked. K-boost will not harm or damage your gpus. 

 2 670 GTX FTWs running 1254mhz core/3707memory(+58/+600/145%) 48C

 
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Hi all
After i enable KBoost sometimes i will get signal lost to monitor forces me to hit the restart button.
Im currently running Sli 770 with k boost on the 2nd gpu will show as stock clock 1150 mhz and 1st will show the overclocked value any idea **** is going on.
Doing my head in been searching around the forums for the past couple of days
any help appreciated
lou

K-boost gives me a locked 1150 on the core. doesn't raise a sweat doing it..

I've never tried K-Boost how does it work ? If i enable it do i raise the  K-Boost all the way up to max for each card ? Do i have to raise the over-voltage ? 

oG kill3r
I've never tried K-Boost how does it work ? If i enable it do i raise the  K-Boost all the way up to max for each card ? Do i have to raise the over-voltage ? 

K-Boost allows users to lock their GeForce GTX 600 cards to Boost Clock/Voltage, even in 2D mode. K-Boost needs to be disabled when installing/uninstalling the graphics driver and when enabling SLI (once SLI is enabled K-Boost can be activated).