yeah ok, the Cobra was a smal fast light car, I did forget abou that one, but it had nothing the euro car couldn't compete with. but from the factory, you can't just make a muscle car turn as well as my civic would with the same amount of $$ droped into it. they are extremely heavy, and not to mention the very common leaf spring suspension in the back. They were pigs as far as driveability went, and they weren't very efficient, as compared to import / Euro cars of the same time period.
Just look at the state they are in now. There is a very good reason why adding a header to an import, or adding and exhaust system only gives you 3-7 horse (usually); or adding variouse other bolt on performance parts. The American cars come so inefficient from the factory that adding a new set of headers gets you 30 horse, or a new exhaust system, where the imports are designed very efficient. They have big engines to componsate for their shortcummings.
They just weren't designed to be cars that performed well, unless you were going in a straight line. Just look at what production car racing today. it is filled with quite a few Teg's BMW's Mercs porsche's, and then a few Vetts and the odd viper. the first thing to go off the track is the viper usually because it is soo ass heavy that it just can't keep up with a Porsche or a BMW around the corners. and they can cost quite a bit less right out of the factory; If the american cars were so great with customisation, then you would see a lot more being raced on stracks that had more than 4 left turns.....
but thats just my opinion......
Mark