the biggest problem I found with my dohc turbo were the conrods. I broke 3 engines with the same failure (1st cyl conrod),one was with c20xe forged pistons and 8:1 CR.
Pistons were right for me running around 11-11.5:1 of AFR on high boost and good ignition without knocking (up to 1,1 bar in high revs, limited to 0,7 below 4500 to avoid high torque, and ford MLS head gasket and a set of camshafts for na engines with more overlapping than std ones)

If you are with std head gasket don't go above 0,6bar.



But today you can get forged conrods and with c20xe forged cheap pistons you can make a good combo. I'm building an engine with this pieces.

http://www.maxspeedingrods.co.uk/hig...lts-x4pcs.html