First Gen F-Body LS-2

[PTAddict]

There are probably hundreds of posts on LS1Tech.com relating to this topic, but to generalize, on a performance cammed 5.7L or 6.0L, shorties are worth minimal to no gain over stock manifolds, long tubes can be worth 20-30 HP and maybe even a bit more than that in torque. The higher end designs with merge collectors do seem to be somewhat better than the conventional cannister-style collectors, but not hugely so.

Edit: Funny, I was typing my response before I saw Jody's, so there seems to be some consensus here.