Back in the mid 70's I was en-route with half a dozen buddies on the way to Santa Pod for one of the big meets. The '65 Galaxie sedan I had at the time had some carb issues and I was pulled over on the hard sholder with my head under the hood fixing it. Back then the M1 was a relatively tranquil place to be earlier on weekend mornings and 100+ mph speeds (in the right car) were quite feasible for extended periods with little chance of being apprehended by the boys in blue (but not in a 289 Galaxie!).
I heard quite a loud powerful and unusual engine sound coming-up from behind, obviously travelling at high speed......and in fact iy was travelling at such a high speed by the time I stood-up and looked to see what it was........John Dodds 'original' 'Beast' had already driven past and rapidly disappeared from view over the crest of a slight incline on the motorway. Most piston aero engines develop power below 2000 rpm so it actually didn't sound very fast..........but it was fast, seriously fast......no doubt well in excess of 100 mph......so fast in fact that the section of cars that were following it (mainly American, so a couple period Corvettes, Chargers, Cuda's and other muscle car plus a couple of E types) also presumably all en-route to the 'Pod were trailing behind - probably about 12 -15 vehicles trailing behind Dodd's car. An amazing sight and sound forever etched in my memory. Don't know if John Dodd was also going to the 'Pod - don't remember seeing the car there.