pistons

[Billla]

You're maybe getting a little hung up on the relief thing Omnivec nailed it - it's just a manufacturing shortcut so the pistons can be used in either bank. Although it has nothing specifically to do with the quality of the piston, typically the "rebuilder" pistons are 4-relief.

In terms of CR, 2 reliefs are generally around -5cc volume; doubling that to -10cc can mean about a .5 drop in CR. Even flat-top pistons will likely have valve reliefs.