21lb is like stock I believe. And turbo flywheel is no different than any other 240mm flywheel.
Cool thing about Fidanza is it's both 225mm and 240mm so any clutch, turbo, N/A 2+2 will bolt up. A matter of fact, my clutch is for 300zx.
I really have almost no lag due with 3.90 and 11lb flywheel (I know it's not the best gear set) It's almost like driving an automatic with 3000rpm stall.
You got 3 inch downpipe? I know that helps. and smaller, shorter diameter IC pipes/