Can a GTX 660 SLI work with a OCZ 550w 80+ gold modular PSU?

I have a custom PC with an Intel i7 3770k, Sabertooth Z77, 2x 8GB Corsair RAM, 2x 7200 RPM IDE HDD (300GB & 160GB; PATA to SATA converters), 1x WD Green SATA HDD (2TB), 1x Samsung 840 SSD (250GB), Zalman Z9 Plus with 6 120mm fans (2 LED) and a Hyper 212 Evo with 2 120mm fans in push pull. Currently I have one Asus GTX 660 (non-ti; GTX660-DC2O-2GD5) in it and it is running just fine with the PSU I have. When I first built this PC, I had no intention on using 2 fairly high end video cards in it. In fact I was planning on using the HD 4000 for the time being, and then the 660 was released and its price and performance made it irresistible. Newegg had a sale a few months after it was released and I got one for around $215 plus a free copy of Assassins Creed 3. It has been running strong and taking any new game I throw at it in high to ultra settings for the last 6 months. Then, as a regular newegg daily deals troll, I landed on the same exact make and model graphics card now only $168 after a $40 discount (off its release price of $250), a $20 promo code and a $20 mail in rebate. So naturally, it is on its way to me at the moment since it is the perfect card to pair with my current, identical one in SLI.

I am concerned that my 550w power supply may not be enough. I have done a few searches and have read of people asking if 650 to 750 was enough. I did go to the site below and entered all my PC's info. When factoring in my overclock of 4.5 GHz and the two GTX 660's in SLI, the fans, HDDs, RAM, etc., the PSU calculator said I needed at least 492w.

Am I going to experience sudden shutdowns or BSODs if my system draws too much power that the PSU can't handle? Will my PSU die an early death if it is being worked too hard with this setup. Or, is it adequate?

I have read other posts about testing the wattage of your PC using a kill-a-watt or a multi-meter. One method to find wattage is to find amps and volts then multiply those values. I have a multi-meter. Should I test the amps and volts? And where on the PC do you put the leads? I have read of other methods that use an extension cord in line with the PSU cord, but I'm not crazy enough to try that.

I know my motherboard and CPU setup allows for PCI-e 3.0 x16 with one card and x8 x8 with SLI. How much of a difference does if make if I am using a motherboard capable of x16 x16? I read that PCI-e 3.0 x8 is about the same as PCI-e 2.0 x16. Should I get a better motherboard or is the Sabertooth Z77 enough?

I also read that when you SLI two or more cards, the RAM is only used by one card?

Thanks, and sorry for the TL;DR-ness of my post. I appreciate any help.
7 answers Last reply
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  1. Your PSU would be enough. Just. But efficiency decreases before and after 50%. So for example, the highest efficiency for a 550W would be to pull 275W. In your case, a 1000W PSU would make it the most efficient. Not that I'm saying get a 1000W - no.

    Bottomline: Your PSU is enough but look into investing in a better PSU later down the track. You wouldn't experience random shut downs as those wattage calculators tend to make it at the worst possible scenario.

    The Sabertooth is more than enough. I've seen a review that said even a PCI E 2.0 x4 is enough (which is a quarter that of PCI E 2.0 x16.

    When you SLI two cards, the RAM is not combined. Meaning, if you get 2x 660's @ 2 GB each, it won't mean you'll have 4GB. You will effectively have 2GB.

    If I helped, please select me as the solution as it always helps. Thanks :)
  2. Your computer will only shutdown if the power consumption exceeds that of the PSU. It won't necessarily result in an early death, its just that it will run hotter and consume more power to power those fans.

    If you're going to OC the GPUs as well, then I'm afraid your PSU would not be sufficient.

    It is worthy to note that personally, I would be looking into 650W. Which should be more than enough. The 550W you have is probably enough, but I wouldn't try overclocking anything. If you do intend to overclock, then I suggest a 650W.
  3. Thanks, Oddlyinsane, how do I select a best answer?

    I won't be OC'ing these GPU's, at least not more than Asus has already done, being that they are factory OC'd "top core" cards. According to the specs, the OC is a modest 105 MHz over reference. I am currently OC'ing both my CPU @ 4.5 GHz and my GPU + 50 MHz on top of the factory OC for a total of 155 Mhz over reference. The CPU is only using 35w when it is at 4.5 GHz. I am using speedstep to bring it down to 1.9 GHz, well below the 3.5 GHz stock setting of the 3770k.

    I read that the Asus "top core" binned GPUs use less power than regular ones. So I guess that a factory OC'd "top core" would use about the same amount of power as a reference non-OC'd GTX 660?

    Are you recommending that I not OC both the CPU and the GPU's? Or am I safe with the CPU OC and the factory GPU OC?
  4. Yeah, the factory over clock is not much of a concern.

    You should be safe over clocking the CPU, but leave the GPU clocks at the default from the factory.

    There should be a "pick as the solution".
  5. I have no idea what I did wrong. I don't see a "pick as the solution" button or icon anywhere. I tried changing the original post by doing a full edit and clicking on the box "Request solutions to this Question (not a discussion)" but every time I try to publish it is the same. When I go back to the edit page, that box is unchecked. I tried adding a question mark and words like Can I...? Will a...? etc. at least 10 different ways and it is still showing up as a discussion. Maybe it needs to be brought to the attention of a moderator.
  6. After installing the 2nd GPU and running several stress tests, benchmarks, and high graphic intensive games, I can say that 550w is definitely enough to power 2 GTX 660s and an i7 3770k overclocked to 4.5 GHz. I was even able to slightly OC the GPUs +50 MHz on top of the factory OC from Asus which is a modest total of +155 Mhz or about 15%. The drawback of SLI is heat. Even in my Zalman Z9 Plus with 6 120mm case fans, the avg. case temps went from 27c to 33c at idle and 35c to 40c under load. Before, even under load, I couldn't feel much heat from the exhaust fan. Now, it feels like a small heater under load. I had to turn 4 of the fans around. Zalman uses the top and side cover fans as intakes. I turned all 4 of them out to use as exhausts and was able to shave 2-3c off the case temps and brought the CPU and GPU temps down a bit as well. Overall, I am quite happy with the setup. 3DMark 11 went from a 6,938 to 12,041 with virtuMVP off. Heaven went from a 726 to 1,412. This card in SLI performs about 20% better than a typical GTX 680 or HD 7970. The best part it is much less for both cards.
  7. I would suggest getting a 600-650w psu just to be sure. Although, 550w is enough, bu you'll never know.
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