I am building the showtime 4d and i am installing the engine, my question is if I could use the stock muffler or do I need to go with a pitts style oh yeah i am using the EVO 1.0 engine

Go to the large Showtime thread, do a search and all of your questions are answered there. Most of them anyway.

My son used an Evo 1.0 in his. He mounted the engine inverted and had to use an inverted muffler like this to make it fit. http://www.bissonmufflers.com/en/muf...ing_id=1136942