Why does the LS1 intake manifold look so much different from the LT1 or the 3.8 V6? Does this improve airflow, and if so, why doesn't the LT1 have this feature?

 

It's called Evolution !

 

Because the LS1 is a new design? They didn't a supplier/manufacturer that could make something like that with that material before? Simply didnt' consider it before? I assume it does help airflow, and help position the fuel injectors in a supposidly more optimal place...

 

Cadillac Northstar, around for 10 years, has an intake manifold almost identical to the LS1 manifold. It's all part of the LSx series design for ports, injector placing, etc. It's also lighter than aluminum and doesn't transfer heat as much. Down side is that it's nearly impossible to port.

FWIW, both the LS1 and the Northstar manifolds can be turned around 180 degrees. Northstar folks do it to run the engine in street rods, LS folks do it for certain mid engine sports/prototype racers.