Ok, 100 mpg. We all want it.

The government has a "250" mpg (or 100, 200, or 500) carburetor salted away somewhere.

So you guys are extra smart, let's do some math.

To be useful, lets say 60 mph @ 3,000 rpm.

Since that is a mile a minute, 100 miles = 100 minutes.

100 minutes times 3,000 rpm = 300,000 revolutions.

one gallon = 128 ounces divided by 300,000 revolutions = .000427 ounces per revolution.

No matter how many cylinders we have, we can't use more than 4 ten thousandths of an ounce per revolution.

one gallon of regular unleaded gasoline = 114,100 btu

114,100 btu divided by 300,000 revolutions = .38 btu per revolution.

That ain't much heat.

1 horsepower = 2,544 btu/h

114,100 btu times 0.6 gallons/hour = 68,460 btu = 21.91 horsepower.

It better be a REALLY dinky car.

If I made some basic math error let me know. Don't quibble over SAE VS brake hp. The point is, no matter how you cut it, you are never going to see 100 mpg in a car you would buy. And be happy with it. Or carry a stick of lumber. Or 4 people.

The Honda Ruckus might be your best bet. 5 hp, 43 mph, 107 mpg

Or you can stick with that 30 gallon gas tank times $7 bucks a gallon = $210

Side note: So the gas prices are putting a severe crimp in your budget? Do you run out and get a Toyota Prius? No!

According to Edmunds.com the answer is a Chevy Aveo! The Aveo doesn't get the mileage, but the $10,200 price advantage ($23,770 VS $13,595) makes up for it. Yes, the Aveo is a pile of crap, but the only criteria was best bang for the buck. ($10,200 divided by $4.50 a gallon = 2,267 gallons of gas.)

Interesting Edmunds note #2:

So that SUV is killing you with $100 fill ups? Trade it in on a Toyota Prius? No!

For a lot of owners, you either can't find a dealer that will take it as a trade in, or they will give you less than you owe. You end up paying on the old car AND the new car. The answer is, if saving money is the object, to keep the SUV!