do burnt CD copys sound as good as originals?

As long as the copy is a "bit-for-bit" copy, then, yes, it would sound identical. You run into trouble when you rip a CD onto a hard drive as a compressed file (mp3) and then burn an audio CD later...once data is compressed fidelity is lost forever.

If done right, the copies sound far superior. But the there are certain things that need to be addressed properly: (1)The software used to rip the CD (load it onto the hard drive), where Audio Exact Copy (freeware) is far superiour to others,
(2) the quality of the CD extractor/burner drive, (3) the software used to burn, and (4) the blank CD, where some are better than others (Black Memorex are popular). There are a number of threads on this issue, both here on Audiogon and Audio Asylum, check it out.

i use copies in the car where it makes no difference to preserve my originals.

No difference...a digital to digital dub will cause no loss - you can make 1000 copies if you wish. Bob Katz and many many others have tested this.

If you are convinced that you really hear a difference then you might question the impartiality of your own skills at detecting differences between other components (amps, cables, IC's etc.).....it seems you have been "got" by the placebo effect (your expectations have framed your opinions rather than your observations).

Like Arni, I think burns can sound better. I've ripped originals to Itunes while my Mac is powered by my PS Audio 300. Then I've burned to either Memorex black or gold Mitsui's that have been pretreated with Auric Illuminator using an external LaCie burner powered by the P300 once again. Burn speeds are no faster than 4x. When I take this amount of care, they often sound superior to the original cd. The comparisons are made to an Auric treated original FWIW.