I am new to the tread and i have Question, I herd that if you take the cats off it will back fire. does this mess up the engine

 

You don't have to take them off. You can get a highflow cat and some straight mufflers and it'll shoot a pretty good flame.

 

I have a 3" in and 3" out straight through cat and a collected 2 1/4" into 2" 1/2" straight through mufflers. If I do the "rev it to 7 grand and flutter the peddle" trick I can get black puffs and loud backfires but no actual flames Although, I didn't want to burn up an engine with less than 25K on it. I have the stock manifold with a custom 3" down pipe.