between the 2 and all the lil stuff that goes with it it's prolly 10-15lbs of actually weight and when u have the belt running on the crank im sure it has to take some hp to turn them... i was very suprised how much they weighed when i took mine out... from what ive read they are there to keep the vibrations down that you might get when you get into high mileage. one of the reasons honda last so long compared to some other manus..

i havent seen the bisi block off but i will vouch for the kaisen kit