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On Tue, 19 Jan 1999 02:01:21 -0500, you wrote: >>Oh yes theT3 do too!! most dont anymore as nearly all engines >have had >a >>valve job by now and the heads machined. without this the CR >will be >too >>high (MUCH too high) and they will run hot and detonate. > > >Now I are confused... How would removing metal from the combustion >chamber (enlarging the chamber), increase the compression ratio? > >Scott > > > >Scott Keck >Luftwagen Gruppe 1 If you really want to get into it(and if you're going to build an engine, you need to), get Gene Berg's technical articles. They have all the gory details on head mods and how to calculate compression ratio. Basically, when a head is overhauled, the sealing surface between the head and cylinder barrel needs to be renewed. This is done by flycutting(flat milling) that area. This reduces the volume in the head's portion of the combustion chamber and raises the compression ratio(also removes the chamber step, if present). The ratio can be controlled by ہS ring shims under the base of the cylinders to space the cylinders out . Unless you're using all new parts, this needs to be done. As you might imagine, these shims have to be precision made and there's some pretty nasty pieces of junk out there. About the only way to tell is to take a mike along and measure the purported thickness and buy decent stuff. You don't want old tincan or heat-duct material, spring-tempered shimstock is the best. Now there's some other milling that the performance guys do called semi-hemi milling, this does increase the chamber volume, usually done in conjunction with larger valves, high-lift cams and other such performance mods. Not something that's compatible with stock FI, so I've never explored it too much.. ------------------------------------------------------------------- Too much? Digest! mailto:type3-d-request@vwtype3.org Subjbscribe