question about shorty headers

almost none. they flow about as good as stock('kay, may be tiny bit better), and sound about stock. Spend your money elsewhere i say.
If you MUST install shortie, I would go with JBA tho
 
My friend is getting JBA shorties put on his Mach while the dealership is putting a new head on his Mach for the head tick problem. I'm really curious what kind of power he gets from them. He bought an SCT 2 and he's gonna get his Mach dynoed and tuned afterwards.
 
there will no real noticalbe sound change. you will gain a bit of hp up in the band. you will lose power low in the band so you will have about the same 1/4 time. the car will pull a bit higher in the upper band.

I would not even think about shorties. if you want headers do longtubes. If you want more power but that $$$ somewhere else.