I dont know its four random people and it wasnt a complete apples to apples comparison. the one guy added more to his setup then just shorty headers. Not only that you arnt running properly with out having the computer retuned with headers. I know your going to say that's more then just bolting up headers but your not going to have the right AFR with out it. Again as well depending on mods results will vary greatly. Somone running a 383 wont want to run shortys. as well not all Long tubes and shortys are equal. some are stepped some are 5/8 and some are 3/4 and so on.

 

down farther there is one guy that says the shorties are adding good hp and only gained 2 hp by adding lts but no dynos. on the other side one guy also says he gained almost nothing adding shorties. judging by the variables and that the uper gains from the shorties are the same as the lower range of gains with the lts i would say its possible either way, its possible to have almost no gain switching from shorties to lts and its also possible to pick up a good gain doing the switch.

 

Like I said before, without the dyno result it's all speculation. The point here was the 4 cars that had dyno results. some had more mods than others which is pointless because the baseline is before adding headers and exhaust. They were stock exhaust except I had trueduals with the h-pipe. The RWHP differences being;
1) The GM HIghTech post; added Hooker shorty and catback, 17 rwhp 11 tq
2) lt1-xjs post; added homemade shorty with X pipe full exhaust, 17 rwhp 16 tq
3) slow94 post; added LPP longtube with off road Y, 19 rwhp 14 tq
4) Shaefz28 post; added Pacesetter LT, ORY , Magnaflow catback, 14 rwhp 8 tq
True dyno proven exhaust gains. Shorties have a 3" collector.

 

in a latter thread 96lt1m6 said he gained hp by going to long tubes over his shorties.LS1TECH - View Single Post - Long tube vs shorties on a lt1..

speed demond said "I went from 276rwhp to 303rwhp with lt's and a mailorder tune." im going to guess stock manifolds to long tubes. LS1TECH - View Single Post - Long tube vs shorties on a lt1..

and a guy with an lt1 corvette said he gained 15 hp going from shorties to long tubes. LT1 shorty vs. long tube header results - Corvette Forum