This morning I left a post on another blog: Crap Every Time by Barb. To turn the comment around, life is like soup: it is what you make it.

So why, I wonder, am I doing this? Why are you reading it (if anyone is reading it)?

I have just been trying to figure out something in a magazine article (Hemmings Classic Car #24, September 2006). In the Mechanical Marvels column on piston rings, Ray T. Bohacz states, "One quart of oil contains approximately 36,500 drops. If a vehicle is driven 55 mph and consumes 1/864 drop of oil during each piston stroke, then this would equate to one quart of oil burned in 1,000 miles . . . ."

I am a bean counter, not a gearhead, so maybe I missed something, but aren't there some undisclosed assumptions here? For example, don't the gearing (transmission and final drive) and/or the number of cylinders come into it?

Lemmesee:

36,500 x 864 = 31,536,000 piston strokes.

Dividing by 2 gives 15,768,000 piston cycles (a piston makes 2 strokes - down and up, or up and down - per revolution of the crankshaft.) Dividing by 1,000 gives us 15,768 piston cycles per mile.

If Bohacz were an old-time reader of Road & Track, he might have made the calculations easier by assuming 60 mph, since engine revs per mile in high gear is the same number as rpm at 60 mph (remember the Tapley Meter, RIP?). At 55 mph, a vehicle travels about 0.91666 mile per minute. Stand that on its head and it takes about 1.0909 minutes to go a mile. The mind boggles. Anyway, 15,000 is a lot of rpm for a passenger vehicle, so Bohacz must be talking piston cycles rather than engine revolutions. The cars I've driven recently do a little under 2,000 rpm at 60 mph in high which, in those cars, has usually been an overdrive.

Dividing 15,768 by 2,000 gives 7.884 so I conclude that Bohacz was contemplating an 8 cylinder vehicle. Did he work backwards to come up with 1/864 drop of oil, or is that some SAE rule of thumb?