Quote:
Originally Posted by Christ
Can you answer your own question?
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I wasn't involved with cylinder heads when worked in an Eng. Dept., but I have some guesses:
It would make the whole assembly less compact. Pushing the guides "out" also pushes springs, rockers, or cams, out.
Valves would have to be longer. If they are longer would they also need larger diameter stems? Then the valves get heavier too.
It could compromise guide life. Yes, even if the guide ultimately was the same length as "baseline". Greater unsupported span of valve stem. Shorter guides likely lead to faster wear via less bearing surface, greater leverage for the nonlinear forces acting on it.
Heat transfer to the guides is a major conduit for valve cooling. Maybe there is some detrimental effect involved with that?