Yawn. I know this forum is populated with people unaware of any history before 1970, but PLEASE go check out the rich and impressive array of auto makers the USA has produced.
Stutz DV-32, 1931: Twin OHC, 4 valves per cyl, synchro 'box, etc.
Miller/Offenhauser: Similar to above, big-bore 4 cyl cars, fast as stink.
Dobel: The most efficient steamer ever built, silent, fast, luxurious.
Duesenberg: Perfected centrifugal supercharging, 320HP from 8 ltrs. In 1932.
Cadillac V-16, Lincoln K-Series, Peerless, Packard.
1904 Sterns: Hemi, 4 valve, OHC, trailing arms, synchro 'box, rack & pinion.
I've left out obvious makes... because the criteria is Best American car ever made. Parts and engineering come from all over the globe now and have for many years. Ya gotta go back for the truly innovative.
As for modern iron, the C6 Vette is about as good as it gets for production.
Saleen and Mosler are at the top for bags 'o bucks types.