Mods and exaust

allright thnx guys...i got another Q....im sure all of u have watched rally's at one point or another and tha fire comes out of tha exaust when u switch gears, now i know that its because its a straight pipe so the cycle hasnt actually finshed when it comes out but does this straight pipe increase any horse power? I kno it is illegal here in canada but still....lol ...and is the horsepower alot greater than most exausts out there? thnx alot