This is 4th Generation 1981 Monte Carlo. Rare because most teams ran Buicks in that year.

Sometimes called a flat-nose to distinguish it from the SS nosed car that was commonly raced in 1983-1984 and then as the Aerocoupe fastback in 1985-1989 up to the mid-year introduction of the Lumina.

The Caprice/Impala are much bigger cars that ran prior to the NASCAR downsizing in 1981. Most if not all the NASCAR racecars from the late 70s to 1980 that are labeled as Caprice are actually Impalas.

On the other side of the atlantic ocean,sometimes you call it Monte Carlo, sometimes Caprice,so really: Caprice or Monte Carlo?