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Posted by David Sherman [216.18.131.28] on Thursday, January 07, 2010 at 02:45:18 :
In Reply to: Food for thought posted by hemimech [71.10.56.36] on Wednesday, January 06, 2010 at 23:35:41 :
With your modern engines, you're probably working with wear limits that are tighter then the manufacturing tolerances on our old engines were. I bet the cylinder boring machines in the engine plants in 1950 lost a few ten-thousandths just in tool wear by the time they finished a block. There was also lots more design margin. Weight savings for fuel economy was not an issue. Cylinder walls were thicker, RPMs lower, pistons longer, and stresses lower all-round. It would be interesting to see, via a full set of dynamometer curves, the performance difference between a 230 that was just inside of its wear specs for its day, and one that was rebuilt to today's standards using the best tooling and machines available today. Maybe there's a real difference, but maybe there isn't.
I'm no engine expert but it seems to me that once the rings fit the bore closely enough that the gap can be filled by the oil film, at the speeds and pressures the engine is running at, a more precise fit won't buy you anything in terms of performance. Another way of looking at it, is if a $500 "freshen-up" job gets you back to 90% of brand-new horsepower, is it worth spending, say, another $3000 to get that remaining 10%? Most of the time, it isn't.
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