How to make the bullet physics update faster?

My bullet physics simulation works very slowly. Let's say, one of the objects is lifting the other one, the takes many many many frames to update to the correct position. Just very laggy... Can I increase the dt? or decrease it, to make the physics react better? The fact is I use the gimpact shapes for the forks of the forklift, I can't decompose the forks into many boxes, it's too time consuming... So I have one 4 bvh static mesh, 8 gimpacts, about 10 boxes... Thanks Jack l_dynamicsWorld->stepSimulation(dt,100,dt/100);