525i engine swap

hi i recently bought a 1990 525i bmw, and im unsatisfied with the horsepower..and i was wondering what kind of engine i can swap it with..and how much it might cost..i have a 1984 633csi..and that puts out 185 horses which is about 20 more but it also has double the mileage..smart? or no? preferably id like to drop in a frigin 540 engine or sumthin..make the bitch fly...thnx 4 ur help

Go to BMRParts.com, they have several wreked 540's that have good engine/trans that would be exelent for a swap