Tune Pipe

HI, to all I am trying to find out what pipes work and don't?
I have a Tamiya TNX with a O.S .18CV-RX engine with a NEW ERA BIG TUBE HEADER.
#1 I just put on a CVEC pipe #165 that CVEC told me to use.
All I can Say is that it sucks!!!!! I lost big bottom and top end Power.I tryed to tune the carb every way I know and I tryed to tune the pipe also no good.
#2 The stock pipe had so much more power over the CVEC pipe
#3 I put on a MGT pipe and Holly S**t it made very big bottom end power and top end was very good.
I would like to know what pipe you are using and how you like it and where it made power to?