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Hello, I’m looking for some advice. My son races a Peugeot 205 GTI in the Classic Stock Hatch championship. Although engine tuning is nominally limited to ‘blueprinting’, one exception is head skimming (and consequent CR increase) which is allowed. The consensus among the front runners is that we should be targeting a CR of 11:1. However, we believe the head may have had a light skim in the past. How can we confirm that? Is there a datum from which we can measure? Is the original depth of the combustion chambers known? I understand the CR from the factory was 9.8:1. If we assume for a moment the head had not been previously skimmed, my calculations based on: CR = (Swept volume + Unswept volume) / Unswept volume Give me a figure of 0.995mm to be skimmed off to achieve 11:1 – does this sound right? This figure would be reduced by any previous skimming measured as per my first question. All the above assumes the head gasket thickness remains constant. However, I noticed that it is possible to buy different thickness competition head gaskets. Has anyone had any experience of these? Or can recommend a particular gasket? We live in Essex, there are several local engine machinists, but these are not motorsport nor Peugeot specialists. Is there any reason we should not ask one of these to skim off 0.n mm? Or is there an advantage traveling further to a Peugeot and/or motorsport specialist? I’m thinking things like having fixtures to hold the head at the correct angle? Has anyone any recommendations of machinists? Thank you in advance.