I wonder why no one appears to be designing and building a new airframe to have a pop at this?
Both the recent record holders have been modified WWII designs
(not taking anything away, just wondering)
Suspect a lot has to do with horsepower. I mean there's only so much you can get out of an IO-720, arguably the highest HP current crop of piston AVIATION engines out there.
The Pond Racer (mentioned above) was a VERY viable candidate, but it was a twin.
And then there's "Turbulence". A Lancair with a PT-6 'something' spooned in for power. Totally insane speeds, but it's a turbine. Sure cleans up in the SARL races though!
Rick