I have an Xu10j4rs in my 205 with forged pistons about to go in for 11.5:1 compression. As far as I know the head hasn't been skimmed. The engine builder is worried that the quality of 98 octane in Tasmania is so poor that 11.5 could cause issues with pre-ignition. I have read that dynamic compression is more important than static compression but these things are a bit beyond me. The inlet cam being used is a Cat Cams 4903109, duration at .1mm = 274 and a max lift at TDC = 2.0 mm.The ignition is mapped via a Haltech E8 running direct fire if that makes any difference.
Have people had any trouble running this kind of compression on pump fuel? Would it be sensible to run a slightly thicker gasket to reduce compression (say a 1.4mm xu10j4 rather than the 1.2mm xu10j4rs)? I have noticed that Cometic gaskets are available to order.
As a side note, I ordered the pistons (86.5mm) and rods from Pure Performance Motorsport in Melbourne and they delivered them within two weeks of the order going through. The valve pockets seem suitably large ...