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We are not talking about rod ratios, even though those are all over the place with vintage and modern engines. And you can leave out all the water cooled engines, if you like. How about anyair cooled CB, KZ, GS, Triumph, Vincent, Harley, etc. Aside from that, water cooling does not prevent cylinder growth. It just removes heat better from metal than air, thereby managing to keep parts in a narrower temperature range.
Dilavar studs on paper seem like a good idea, but they brought a reasonably high failure rate with them. I have never heard of any other head stud failing at the same rate.
If you observe the ridiculously low head torque for Dilavar studs, you are limited to about 600-650hp max (not accounting for detonation), before cylinder pressures lift the heads. If you are willing to limit your HP to below that and want to inspect your engine for broken head studs on a regular basis, go ahead and use them.
But with all the other air cooled engines out there, can you tell me why Porsches are the only ones that need Dilavar to keep things together, when everyone else is perfectly fine with steel studs?
But since you mentioned water cooled engines, just to come back to piston to head clearance, as a good example I had a ZX11 that needed .035"-.036" clearance with a stock crankshaft, but when I put in a 5mm stroker crankshaft with the same pistons and rods, the same engine needed .040" minimum clearance. It is all about the internals deforming at high rpm, due to massive Gs being generated by the stroke of the crankshaft.
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