I was wondering if modifying an engine changes the redline. and how much? I have a streetported 13B with aftermarket carb flywheel exhaust ect. What do you think my new redline is?

 

the red line is set to ensure the engine doesn't fly apart and kill itself. Unless you have built the engine for high rpm (lightweight rotars, tiny clearances, reenforced shafts and gears) then your redline wont change. Most of the time however it should be safe up to about 8 -8.5k rpm

 

Typical rotary redline is 8000 rpms.Some say 8500 is OK,so long as you dont hold it there.
Thats about the point where the apex seals start to chatter and e-shaft whip sets in,espcially on the longer 13B engines with heavier rotors.Shorter,lighter 12A's like high revs a little more than the 13B,but for the most part,if you observe an 8000RPM redline,you should be fine.