if i put shortyson my LT1 and leave the stock Y pipe is the sound gonna change or do i need to change the Y pipe?

 

It'll be a little louder and you'll get a bit more power in the mid- to high rpm range (if I remember correctly). Long tubes though are best if you can swing them in your state, which most allow as long as they are EGR equipped and you keep the cats.

 

yes sound will change, be better with matched pipes to the cat back.

 

I could but then I'd have to modify the y pipe which is a potential pain in the ***