Right now on my 87 yz125 i have an fmf fatty pipe with an answer equalizer silencer. I mostly ride trails and i like the torque the fatty gives on bottom but i want a stronger hit on top and dont mind sacrificing some on bottom. What's a good pipe for top-end?
Pro Circuit should make a pipe for that 87 (I've got a 87KX 250 with a PC pipe on it). I've never had any other pipe on it but the PC pipe on mine seems to have a good bottom with a nice bit of overrev.
You could also try knocking down the rear sprocket a tooth or 2. That'll take away some bottom and put the power more toward the top.