Measuring engine specs is really just simple math, but just the thought of manipulating numbers can make some car guys cringe. Count your author among that crowd. The more oddball the number, the more I shudder, and don't ask me to work with fractions unless you want to watch my head explode.
But really, violent cerebral hemorrhaging is not necessary, and often the numbers aren't as bad as you think. It makes a lot more sense if you can visualize the space you're measuring, and once you get over that hurdle, checking engine clearances is not whard at all.
