I am trying to install an aero turbine exhaust to the nissan 350 z 2004. The guy at the shop said it cannot be done because of space issues. I want these on can the pipes go staright from the cat to the exhaust eliminating the factory system? What will go in its place as it will leave a void?

Sounds like a custom job...
You check the specs out yourself yet...
check online too...
info@aero-turbine.com
1-877-COOLFLO (266-5356)
1-801-495-0882
Hope this helps..
CL