You get bigger springs because of spring supply issues.
The heavier springs help valve bounce at high revs.

Hey Dattodude what sort off hp you punching out?do u need to put different springs to suit different cams?

High lift and high revs dictates the need for heavier springs.
The ca18 engines are 25 years old with who knows what thrashing the springs have had.
I dont know that springs and retainers are needed, but I wasnt married back then, so I didnt need to be sensible with budget.
Ive only managed 188kw at 12 pound boost, but forged pistons, turbo, cams are designed for 20-25 pound boost.