Hi Dave. We used fresh OE cast aluminum pistons (L67). These are fine for running quite a bit of boost. I was at 13-14 PSI, and have run up to 16. Problems occur when you go lean and severe knocking ensues, which is what happened to mine.
For what it's worth, I've read hypereutectic pistons are brittle, and not recommended for boost, but there may be exceptions here.
Diamond makes a set of forged pistons for a pretty penny, which can tolerate lots of knock, but a downside is they have piston slap when cold. It's just something I read numerous times from those running them. Not a huge deal for a race car, but not something I wanted for my daily.
Also the OE head gaskets are very good in the L67. We used these and of course the updated OE metal LIM gaskets for the rebuild.
If you've never had your fuel injectors cleaned and flow tested, this is a good time to do so. https://www.mrinjector.us/
Love the extra mid/high power from 1.9:1 rockers. One of my favorite mods for these engines!
_________________'98 SC Riviera • 281k miles • 298 HP/370 TQ • 0-60: 5.79s • ET: 13.97 @ 99.28 • 4087 lb • 20.1 avg MPG • Nelson Ledges Lap: 1:30
3.4" pulley • AL104 plugs • 180º t-stat • FWI w/K&N • 1.9:1 rockers • OR pushrods • LS6 valve springs • SLP headers • ZZP fuel rails
KYB GR2 struts • MaxAir shocks • Addco sway bars • UMI bushings • GM STB • Enkei 18" EV5s w/ Dunlop DZ101s • F-body calipers
EBC bluestuff/Hawk HP plus • SS lines • Brembo slotted discs • DHP tuned • Aeroforce • Hidden Hitch
^^^ SOLD ^^^ '05 GTO • 85k miles • 0-60: 4.8s • 16.9 avg MPG • Nelson Ledges Lap: 1:26
Because fun'70 Olds Ninety-Eight Holiday Coupe • 116k miles • 455 Rocket V8
Because cool'95 Celica • 152k miles • 0-60: yes