Shearer Pipe

I have experience..had a shearer and used it twice. On the same quad a shearer, lrd,toomey, dynoport and fmf. Honestly the shearer was the lowest on the totum pole for all around performance. My son races mx so bottom and mid is the key and the shearer which is a bottom end pipe didnt cut it.

What's his engine setup and which exhaust did you guys prefer out of all those?