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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.

I posted this in the other video's thread but think it's worth it's own topic, purely because the amount of ground it covers. Some of you may have read vizards book, whilst this concerns the A series engine, it references topics we regularly discuss in the modified engine section up to and including. He generally explains things pretty simply, and if you want to understand a bit more about a number of topics including those below, watch it. Filtration Fuel atomisation Compression ratios Dynamic compression ratios Brake Specific fuel consumption Porting Valve design Valve seat design including 3 angle valve modification Lifter / bucket diameter Roller rocker design and limitations Ramp angles on camshafts Cam shaft timing Carbs vs injection (lucas mechanical) Valve shrouding Bigger vs more valves Decking blocks Squish height Burn time Rod lengh / ratio Octane ratings Water injection and some more that i can't remember Cheers J