Originally Posted By: SR5
Cujet: Which remain about 0.001 inches per inch of bearing diameter
SR5: Glad to hear that is still valid, it's what I learnt when I was machining, but that was awhile ago. A Thou per Inch, easy to remember, even for somebody raised on metric.
It is still valid in many situations. The exception would be purpose built racing engines with specifically designed, robust components. This does not include highly modified street car engines.
If we purpose build an engine for very high specific output, we take steps to minimize distortion in all critical areas. This results in robust components with well understood dimensional changes under load. Crankshafts, blocks, bearing supports and so on are extremely robust. This allows us to reduce clearances, use thinner oils and reduce friction. Expect costs to start at a low of about $30K for a purpose built Nascar type engine and go up to well North of $100K for other racing engines. Again, these engines are designed for a purpose. Automotive engines are, in general terms, not the same.
Consider my car, a Honda S2000. It's 2.2L engine is designed for 238HP, and it falls short of that in real world tests. However, with my turbo setup, it produces 407 RWHP, or about 440 at the crank.
More importantly, the torque produced goes from 118 foot pounds to 280 foot pounds! (at boost onset, then drops) The crankshaft distortion caused by this torque is enough to create havoc in that engine. The result is to be expected, short life under heavy loads.