a b18a1 block has a longer stroke than a b16a block, so the b18a1 cam duration must be longer to fully charge the cylinder with fuel and air, so if i used a b16a head and cams on a b18a1 block the b16a cams won't fully charge the cylinder and that defeats the purpose of a ls vtec power increase or is there something i'm missing. or ( do you have to use gsr cams or adjustible cam gears.) please leave feedback.

 

everything is on one timing belt, therefore everything is in sync and ok

 

no it dont defeat the purpose, you'll still make power.
smaller cam will make power peak earlier, thats all.
Example: if you put r cams on a b16 power will peak higher in the rpm range than the b18c5.