Originally Posted by S10 Racer
Thats a typical problem with the old glasspacks. The back pressure they cause (somewhere around 15-18psi) is robbing power from the motor. A good quality muffler like Magna Flow, Walker Ultra Flow, Thermal, A'PEX, Borla, etc. are good low back pressure mufflers. Any of these will only cause about 1-2psi back pressure. It's not the tuning, it's in your mufflers.
Please show your references for these data. I'd be very interested in reading it.