pistons. I believe the early production Viper engines had forged pistons before switching to cast to save money. Some Honda engines have forged pistons from the factory. So it is not limited to pro stock applications like you say.
The stock piston is heavier than forged pistons because cast pistons are weaker and require more mass to make it stand up. Forgings are always stronger than casting hence require less mass. Also the stock piston has a heavy thick walled wrist pin. Most of the weight savings is in the wrist pin by about 50 grams per pin vs. after market wrist pin. The weight savings in the forged pistons vs. cast is very little. This depends on the design and machining of the forged piston to make it as light as possible without compromising strength.
