I'm for the moment looking at installing one of these on the exhaust side when I get my proper power supply.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835192022
That fan is only 66cfm, I believe the S1 fans are 130CFM. I tried putting in some 120mm 95CFM fans on the output and they seemed to be blocking the airflow more than assisting as the miners ran a few degrees hotter.
I have ordered a fan that is purported to be similar to the stock S1 fans and will report back once I get it
http://www.amazon.com/gp/product/B004YELGR4/
I had found something with 130 but it didn't specify pins and had no reviews.
What are these fans considered ? Are they server fans as is why I can't find something on newegg close to that level.
I put a second fan on (corsair Sp120) and it actually made everything much worse, I've got a lot of X and speed dropped. I removed the second fan and simply OC'ed to 375 MHZ instead of 393 or 400. It did not affect the temp (at least I do not see much difference). I think that room temp is much more important than extra fans.