RM Auctions has quite a slate of sales due for its Monterey Auction on August 17 and 18. Included among the cars are an 1968 L88 CorvetteChevrolet Corvette 427 L88United States of America, 1968 > present1 photo
with the most wins of any Corvette in history, one of five surviving Porsche 904/6sPorsche 904/6Germany, 1964 > present1 photo
, a 917/10Porsche 917/10KGermany, 1972 > present1 photo
raced by Jo Siffert in the Can-Am Series, a 1967 Ford GT40Ford GT40United Kingdom, 1964 > present2 photos
, Bentley Speed 8Bentley Speed 8United Kingdom, 2003 > present6 photos
and Audi R8Audi R8Germany, 2001 > present1 photo
. It is a frankly amazing collection of cars for sale. 

The L88 Corvette is estimated to sell for between $950,000-$1,350,000. It raced throughout the 60s and 70s. It won the SCCA "A" Production Championship in 1969 and 1972. It was runner-up in 1968 and 1970. It also scored a second place finish in class at the 1969 12 Hours of Sebring and won its class in the 24 Hours of Daytona in 1969 and 1970. The car won 11 races from 1969 to 1971. The car is currently wearing its 1971 24 Hours of Daytona livery. 

The 1963 Porsche 904/6 is estimated to sell between $1,800,000-$2,200,000. It is one of five surviving six-cylinder cars built for the Porsche works team. It was the second 904/6 produced. It was the development car for modifications during 1963,1964 and 1965 then sold to a privateer team for hill climb racing from 1966 to 1968. 

The 1971 917/10 is expected to sell for between $2,900,000-$3,500,000. Jo Siffert specifically bought the car to race in the Can-Am Series. Siffert raced the car in six of the 10 rounds of the 1971 Can-Am Series but died while racing in Formula 1 later that year. The car was sold and raced in the European Interserie in 1972 taking second in the championship. The car was damaged in a crash at the Nürburgring in 1972 and put into storage for 25 years. The car was rebuilt by the head of Porsche's Rolling Museum in 1998 and has done limited historic racing since then. 

The 1967 Ford GT40 is expected to sell for between $2,300,000-$2,700,000. It is one of 133 built. It was a promotional car that was displayed in the US in 1967, and then sold to a Ford dealer for display until 1973. The next buyer raced the car sporadically and sold it to another buyer who drove the car sparingly. There are just 4,749 miles on the car. 

Two other interesting cars being offered are a 2001 Bentley Speed 8 and 2001 Audi R8. The Bentley took third place at the 24 Hours of Le Mans in 2001, and the Audi is one of five in private hands. The Audi is expected to sell between $1,000,000-$1,500,000. The Bentley is estimated to sell between $1,900,000-$2,500,000.

You can view the entire auction listing here including descriptions of each car.