do burnt CD copys sound as good as originals?

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.

A number of years ago I remember reading an article as to why copies can sound better than the original. I think that it might have been in Stereophile. I don't fully remember what the theory was, but it sounded reasonable. I think that it had something to do with the transition from pit to plateau on the data layer of the original being better defined on the copy. Certainly there are many people who report that copies sound better, although just as many report no difference.

To say that there is no difference merely because a bit for bit copy is being made is difficult to sustain. This argument should apply to all things digital. With this logic, all CD players should sound the same, and all digital cables since it's just bits that are being moved around. Well, we know that's not true, because the timing of the bits as measured by jitter can cause CD players to sound different. So more than bits comes into the equation.

I suppose the best thing to do is to give it a try and see if it works for you.