how can i add btcache to the torrent i want to download?

Nearly a month ago i added a torrent to download in utorrent 3.3 and surprisingly i got speed of about 1 mb/s. which is 30x faster than that of my downloading speed i.e 30kb/s. From that day i downloaded all torrent with speed 1mb/s. I later got to know that there's something called btcach which is giving me this amazing speed. But sadly i'm not getting that speed now. I didn't changed any setting of utorrent. It is same as before. Now the question is how to get that btcache so i can download torrents at 1mb/s speed. Thanks in advance... :)