If you don't plan on running crazy amounts of boost then you could replace with stock ones. I am using new stock pistons with gold coat and polymolly coatings by swain tech. The coating spreads heat evenly over the piston and reduces the chances of detonation. I think I should be able to run 18-19lbs of boost safely. The stock pistons run about $240 for a set and $230 for the coating. Forged pistons like JE run about $730 - 770