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Dear experts on 205gtidrivers I am restoring a BX TZi configured as it was sold in North Scandinavia and perhaps Switzerland too (DDZ engine with the Fenix 1b monopoint system). I have to change the block of the engine due to a crack that leaks coolant. For that purpose, I bought a D6A engine with the same block as other 8V XU9 engines, but upon separation of the parts I started thinking (dangerous): I have seen posts on combining heads and blocks from XU engines on this site. I have, however, not come across any that combined the cylinder head from a DDZ (most likely similar to D6B?) with a D6A block that comes with flat piston crowns. The head from the D6A engine clearly has a larger combustion chamber volume than that of my initial DDZ engine, which in turn then has the asymmetric, chute-like cut-outs in the piston crowns that I first thought were to the benefit of direct injection engines (to mix petrol and air upon injection). It seems that these differences causes the D6A engine with flat piston crowns but larger combustion chamber and the DDZ engine with non-flat piston crowns and smaller combustion chamber to have about the same compression ratio. So here is my question: will the increased compression ratio from combining the flat pistons of the D6A and the small combustion chamber of the DDZ improve the performance of the engine or will it rather impose problems like 'pinking' and lack of control from the engine management system? I suspect that there will be no problems with flat pistons when it comes to the valves of the DDZ head actually protruding into the cylinder volume as these open, since the valves in this position also reach into area covered by the piston crowns of the non-flat original pistons. Are any of you familar with the effect of this or a similar combination (I speculate that both the head and the pistons that I am talking about here occur in other versions of the XU9 engine and maybe the XU5?)

A little bored given the crappy weather, and mindful of the mileage my 205's original engine is racking up, I was thinking of building up a higher compression 8 valve lump for my 205, 1.9 with 1.6 pistons, and am wondering what the limitations of the standard top end is, and would standard bottom end parts work as a budget build without grenading given the 8 valve tends to produce its power at lower rpm? the questions I have are as follows: at what point does the head need work, would I benefit significantly from doing so at a fairly low level of tune? IIRC I do have a lightly tickled 8 valve head in the shed already, the exhaust ports have been smoothed up a bit I am thinking as with most pug engines and going from what I have seen of Sandy's engine builds is that the valves are plenty big enough (though I'm off to read this topic again shortly... http://forum.205gtidrivers.com/index.php?showtopic=31290&st=0 ) a quick working from memory of dish and chamber volumes indicate that I'll be around 10.8-1 with an unskimmed head, no doubt the head I have has been skimmed in the past. what is the max lift for std valve gear? I take it that RPM is more a bottom end concern given the tappets are solid as standard. for the bottom end, I am thinking as mentioned of some XU5JA pistons as they have a smaller dish and bump the compression, some standard 1.9 rods checked for weight discrepancies. I do have an XUD9TE crank to hand which is reputed to be forged steel. I have an XU7 block to hand, and an XU7 oil pump, as well as XU9j4 10J4RS and XU10J4 oil pumps. Camshafts, not sure what I could use, may depend on limitations of standard valve train, IIRC I do still have a PTS max Torque cam if it has not rusted away in the garage