Tuesday, September 6, 2011

Fun with Calculators

A while back, I posted about the weird, mathematical places my brain goes when I am alone in a car. It probably says something very Freudian about me that guns and math occur in the same train of thought. However, that post turned out to be very popular. So, whatever.

Since I am back to commuting again on a regular basis for the first time in about three years, I've gotten back into my solitary, reflective ways. As I was on my commute to law school this evening, I was reminded of a period in my life not too long ago when I was forced to commute from Dallas to Houston on a weekly basis for work...for a period of two years. I chose to make the four hour drive myself in my own car instead of trying to fly or take the bus.

There is a reason my 2000 Nissan Maxima has over 312,000 miles on it, but I digress. 

It was during this time of massively insane commuting that I had another fit of mathematical mind wandering. Since gas was selling for $3.89 a gallon at the time, you can guess where this is going. 

Yep, I just had to try and figure out how much money I was spending every time a cylinder in the engine fired.

And, being the sharing type, I now bequeath this knowledge to you. 

My car has a 4 stroke, 6 cylinder engine with an 18.5 gallon gas tank. In a 4 stroke engine, a cylinder fires once for every two revolutions of the crankshaft. Let's start our gas mileage calculations assuming you maintain an average speed of 60 miles per hour and that the car gets 30 miles to the gallon at that speed. My Maxima's best observed MPG so far was 34. So, it's doable.

60 miles in 60 minutes (1 hour) = 1 mile per minute
30 MPG at 60 MPH = 2 gallons per hour
18.5 gallon tank divided by 2 gallons per hour = 9.25 hour range/tank
18.5 gallon tank times 30 MPG = 555 mile range/tank
2100 RPM at 60 MPH = 126,000 crankshaft revolutions per hour
2100 RPM = 1050 individual cylinder fires per minute
1050 times 6 = 6300 total engine fires per minute
6300 times 60 = 378,000 fires per hour
2 gallons per hour = .03333 gallons per minute
6300 times .033333 = 189,018.9 fires per gallon
128 ounces per gallon
2 gallons per hour times 128 ounces per gallon = 256 ounces per hour
1 ounce = 1.8046875 cubic inches
128 ounces divided by 189,018.9 fires = .00067725 ounces per fire (= 0.0012222246094 cubic inch/20.029 cubic millimeter)
$3.89 per gallon = $0.3039 per ounce
$0.3039 per ounce times .00067725 ounces per fire = $0.00002058 per fire

So, to recap, every time a cylinder in a 6 cylinder engine running at 60 miles per hour averaging 30 miles per gallon, you are spending a little over 2 one thousandths of a cent. They tend to add up pretty quickly though.


  1. Now that is right up there in my top 10 things i didn't need to know, but found quite interesting...

    just saying....:o)

  2. Mr. Daddy, you're welcome. Just consider me your friendly, neighborhood source of absolutely useless, esoteric but fascinating information.


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