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- #4,156
21-169 engine here, over 14k, hoping it doesn't fail driving from Virginia to Colorado, Moab, and somewhere on the Pacific coast, end of the month
How many Miles to be ' in the Clear ' ?
for ' Hot Zone ' engines, regarding dropped-valve failures
- from B6g data the average Mileage is low
- avg about 3000 mi - w standard-deviation about 1500
As the mileage goes above 3000 you would expect the engine to be more reliable, i.e. less vulnerable to dropped-valves
- this expectation makes sense
But how much more reliable ?
- as the odometer keeps rolling, how much safer is it ?
To answer this depends what type of distribution the events are following
- below are four types of possible mileage distribution - Normal, SHASH, Johnson, and Weibull
Normal distribution ( green line )
- this distribution would give a 6-sigma value of about 12,300 mi
- above this mileage you would expect the reliability to be about a million times better - w/r to dropped-valves
- however, other distributions have higher probability density above the 3000 mile average - e.g. Johnson & SHASH
SHASH distribution ( blue line )
- of the four listed, this is the best fit of B6g data
- for std-dev, I haven't done the calculations w transcendental functions
in General
- an engine w over 12,000 miles is prob at least 10,000x less vulnerable to dropped-valve failure
Common Sense Approach
- the plan mentioned by several people makes sense - just drive the heck out of it to get the mileage up, then don't worry about it
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