I recently wrote a piece about cars powered by compressed natural gas (CNG). This is a rather large subject to treat in barely 20 column inches. Sort of like trying to fit Imelda Marcos' shoe collection into the trunk of a Corvette.

So, there were some details that were omitted, and those omissions prompted some reader mail. Let's look at a few of those questions, and then go on to some other reader inquiries.

Question: Do you have either a list of or link to the CNG stations in our metropolitan area? - J.P.

Answer: You can find the eight in the Philadelphia vicinity by going to cngnow.com and clicking on "stations."

Q: You said that the cars and trucks on the market that can burn CNG are powered by converted gas engines that can run on either. Assuming we develop an adequate CNG refueling structure, wouldn't it be cheaper to build a car or truck that just runs on CNG? - H.L.

A: Yes, it would, in more ways than one. First of all, you would save the cost of a gas tank, a fuel pump, the gas lines, the gas injector rails, and the device that automatically switches to the gasoline supply when the CNG runs out.

You would also get substantive improvements in power and fuel economy because a dedicated CNG engine could utilize significantly higher compression ratios than an engine that must also be able to use gasoline.

Compression ratios signify the extent to which an engine compresses the fuel/air mixture it burns. A ratio of 10 to 1, for example, means that the engine is compressing the fuel/air charge into one-tenth of the space it would normally occupy. So, the higher the ratio, the more you are squeezing the mixture - and the more power you are obtaining upon ignition. This increased efficiency also translates into better mileage, since you don't have to use as much fuel to do a given amount of work.

You could also make the case that getting rid of the gas tank frees up potential cargo space because you could mount the CNG tanks where the gas tank used to live instead of in the trunk or truck bed.

Q: Which has more of a future, CNG cars or electrics? - M.E.

A: I think there's a significant life hereafter for both because both have their strengths. Since a comprehensive refueling infrastructure has yet to be built for either mode, the CNG has a marked current advantage in range. It is also more practical than electricity where substantial power is required - as in the new big Ram pickup powered by CNG.

Electrics, on the other hand, are even cheaper to run than CNG vehicles, and even cleaner, although that latter edge can be diminished a bit if they are charged with electricity from a coal-fired generating plant.

On other matters:

Q: I'm torn between a new Hyundai Sonata and a Kia Optima. Which do you suggest? - F.N.

A: These two corporate cousins share structure, mechanicals, and a generous warranty, so that's a wash. I do prefer the Optima's styling, though.

Q: You are always [complaining] about imitation wood trim in cars. I have imitation wood in my car, and so do some of my friends and relatives. We don't have any problems with it, why do you?

A: I happen to think that the materials you use to make cars, houses, and home furnishings ought to stand on their own merits, and not pretend to be something else. I wouldn't buy a car finished with ersatz veneers for the same reason I wouldn't put a ceramic Bambi on my coffee table.