Also guys, there's more to pistons than weight.
Silica content determines how much the pistons expand. Some forged pistons contain almost no silica. Other can have up to 11%. This changes the expansion rate and how much clearancing must be done for the skirts.
Ever wonder what makes a hypereutectic cast piston hypereutectic? Silica content over 12%. In fact most are 15 to 21%
Silica hardens the alloy the piston is made from. This increases durability. It also allows the top ring groove to be located closer to the top of the piston to reduce emissions.
But that comes at a price. The more silica, the more brittle the metal. Less silica? Higher expansion and more clearancing is needed in the build. This is why some forged piston motors sound like diesel engines when they start up cold. After they warm up and the pistons fully expand in the bores, they quiet down.
It's a balancing act. You've got to determine what you want out of your motor, the types of power adders you're going to use (turbo, n02, etc.), determine the RPM range it's going to operate in, and then select the piston that best suits the job.
Do you know that many manufacturers make pistons slightly elliptic rather than round? Some are up to .035" shorter across the wrist pin axis than the major axis to compensate for the different expansion rates in the area that has thicker piston mass by the wrist pin.
So to really work out what you want to do, if you want to truly "design" an engine rather than just "throw one together", you need to know not only your power goals, but how you are going to get there. What turbo will you use? What speed will you have to turn your little 3.0 liter motor to boost that big ass turbo enough to hit the goal. Will you use nitrous? Will you be able to live with the high boost threshold without it?
Get all of that together, then you'll be able to calculate things like mean piston speed to determine how much stress you're putting on the rods. You'll be able to tell if you need a piston that's more forgiving of detonation (low silica pistons take it better, but are softer overall).
What's the use of the car? Daily driver? Lots of cold starts? You might not want a low silica piston. Just a weekend driver? Maybe a loose bore with a more forgiving piston works better for you.
There's a lot more to this than just weight.
