Forty two years after this event it still amazes me. I remember watching those TV commercials and thought it was the Comet down the street. Any idea on the modificatioins?
Mercury Motors, in an effort to boost sales of the Comet, put 5 Caliente hardtops on the track at sustained speeds of over 100 mph for 22 hours per day for 40 days. 30 skilled drivers (one was Buddy Baker) took turns working 6 hour shifts to cover 2500 miles per day. They had to drive well over 100 mph for 22 hours to average over 100 mph for 24 hours. The other two hours per day were for maintenance.
All 5 cars were standard 3 speeds with stock 289 4V (not k-code). All but one ran perfectly for the 40 days and it only had a broken valve spring. The total miles driven by each was 130,080. The cars broke over 100 world records for speed and endurance plus over 300 American records - according to the article.
After the durability run, the cars were taken back to Dearborn to analyze engine wear. The only significant wear on the engines were the piston pins. All other measurements were within production limits.

Does anyone know who the other drivers were? My memory seems to think that Frank Warren may have been one of the drivers.
I also seem to remember that the cars kept going and the ads kept coming! Has there been a 'tougher" test of "stock" showroom automobiles?
Henry