gdg1006

Does anyone know if it matters which way the exhaust flows through Flowmaster 40 series mufflers. I have a 02 GT and mine are mounted with the center mounted inlet facing forward. On my dads 02 GT his are facing with the center mounted inlet facing backward. His exhaust was done at a very reputable shop and mine were on the car when I bought it. Mine sound really good, but I was wondering if it was robbing HP.