Increasing Hashrate for Sapphire 7970hd

[TheFuneral]

I currently have four of these cards

http://www.amazon.com/Sapphire-DL-DVI-I-SL-DVI-D-PCI-Express-11197-03-40G/dp/B009B6Y01Y

and am currently getting ~475khs per card. Ive seen people mention getting about ~3000khs for the four cards together. I'm currently getting 1920khs.

How would I go about getting that extra output from my cards?

my current cgminer is this;
cgminer --scrypt --thread-concurrency 8192 -I 13 -g 2 -w 256 -o pool -u user -p pass

Thanks again for your time and help,

[redxs]

you must increase frequency of GPU

[pocoqoco]

The intensity is the mos important parameter to get higher hashrates
try at least -I 17

[larkstongues]

Overclock your GPUs; don't mind the memory frequencies though; they don't matter for scrypt hashing.
Also try raising the Intensity stepwise to about 18 and check what rates you get.
With these cards you can prob. double the thread concurrency.

[uray]

-I 13 is the sweet spot, more than 13 often resulting in driver crash or GPU hang

[larkstongues]

-I 13 is the sweet spot, more than 13 often resulting in driver crash or GPU hang

I've read this multiple times now; however with my Sapphire HD7850 I get the best rates at -I 18 with no errors at all. Since OP got a Sapphire too he should at least try it.

[TheFuneral]

not that I think either of you are wrong, but do you have any blogs/articles that show it? Or just on the forums. I'm open to trying it for a day and seeing how it performs.

Currently I'm running;

thread-concurrency 8192
I 13
g 2
w 256

and am seeing about a 20% reject rate

with 18 I'm getting mainly HW errors. Does your 7850 not do that with i=18?