Dear Car Talk:

I was reading a review of the Kia Optima (next to your esteemed column here in the paper). It mentioned that the base 2.4-liter engine produces 192 horsepower. That works out to 80 horsepower per liter. I started thinking about the car I learned to drive in -- a 1956 Chevy with the Power Pack option: 4-barrel Rochester carburetor and dual exhaust. That 265-cubic-inch (4.3-liter) engine was rated at 205 horsepower, which is 47 horsepower per liter. It's a bit hard to believe that the "performance" version of a big mid-20th-century V-8 engine would have over 40 percent less output per liter than today's run-of-the-mill sedan.

Are engines really that much better, or has horsepower been redefined -- maybe based on today's slimmed-down horses?

-- Gary

Believe it, Gary. There are a number of engines that produce well over 100 horsepower per liter now. And in general, engines today produce far more power, use far less fuel and create a fraction of the pollution. Why is that? There have been a ton of incremental improvements in technology since 1956. First of all, tolerances are much tighter, so a cylinder no longer loses half of its compression through gaps around the rings (OK, "half" may be an exaggeration). Fuels and lubrication are far better. There's been a huge reduction in friction. Fuel injection and computerized engine management allow us to precisely meter how much fuel goes into the cylinders. In your old '56 Chevy, it was like they poured gasoline into the engine from a boot.

And instead of two valves per cylinder, most cars now have four or even five valves per cylinder. That allows the engine to breathe better, taking in air and sending out exhaust much more quickly and efficiently.

We even have variable valve timing, which adjusts the opening and closing of the valves for maximum power and efficiency at different engine speeds.

There's coil-on-plug technology, which sends a much higher voltage spark to each cylinder, with almost no power leakage, since each cylinder gets its own, dedicated coil.

And in the past few years, cars have adopted gasoline direct injection, sending the fuel-air charge into the cylinder at very high pressure, at just the right millisecond.

Then there are turbos, twin-turbos, tri-turbos, quad-turbos, superchargers and turbo-supercharger combinations. Electric turbos and electric superchargers are coming, too.

All of this is why you now see full-size sedans getting plenty of power from four-cylinder engines, when they used to need six- or eight-cylinder engines. And soon we'll be seeing more three-cylinder engines.

When you can easily get enough horsepower out of three cylinders, why not save the weight and add to your gas mileage?

In fact, you already can get a three-cylinder engine in a subcompact Ford Fiesta that produces a very respectable 123 horsepower. It's a one-liter engine, Gary.