There's a couple cars with a jackshaft. The header and pipe was put on by the guy that dyno's and seals all the engines. In the stock class the engines have to be sealed so you can't do anything to the engine. They all have to be the same. Everyone has the same header and exhaust on their cars as well as the carburetors. Air filter has to be stock and sits inside the cockpit of the car which is a pain for most kids. You're allowed to take off the stock cover for it so you get more air. They have an open class where you can do anything to the engine but there's not many in that class this year because of the $4k-$5k engine cost. There's talk about using the stock Honda GX390 engine for the open cars next year but it's not set in stone yet. One kid in the open class hit 69mph at a half mile track 2 weeks ago. My daughter's fastest speed so far is 58mph at the 1/3 mile track. My stomach is always in knots and feel like I'm going to throw up when she goes onto the track and seeing her driving that fast.