Flames is normal and awesome!!! I had them with my s2000 and turbo back 3" exhaust on a N/A motor!!! freaking sweet sound and huge flames. what happens is the hot unburnt gas ignites when it reaches the significantly cooler air toward the end of your exhaust. I always joked with my buddies if they tailgated me at a red light I would melt their bumpers
I have some pics of a Supra at lil tally that I took and it was throwing out 3ft flames!!! it was EPIC!!!