I just replaced my mufflers (and a lot of motor parts). I turned my tips 15 degrees upward. I don't remember the total, less than 90, maybe 75 degrees. Before they were turned so low that I blew gravel away from the car. Some times this was a problem for the cars beside me. I think they were louder. I think the sound (noise) would bounce off the pavement and back to me. I took the Cobra for a short trip today because Friday it's off to the dyno for tuning. Car runs rough now but a re-tune of the chip will fix everything.
It will be next weekend before I can tell if changing the angle upward made a different.
I think I need wider tires
Dwight
P. S. we have 13 Cobras in the area and mine had the lowest angled pipes. I changed mine because I think it will be better. Time will tell.