John, were there significant changes to the rules in the day?
Tyre rules I know did change from time to time, but I always understood there was no real difference in the car-building rules at least until 1983.
The coming of a lot of flow-bench work in the nineties did make some difference in power, of course. But I always thought it was without rule changes.
Rumours of the leading cars all having 1:1 top gears were there from time to time, of course...
It's hard to draw a line in the sand mechanically for vees until maybe 1991 when the 1 untouched component rules changed to minimum weights. The first Rennmax mk2 was 1975 and the first NG Elfin was 1976. They influenced a change in shape form the original type of cars also introduced the remote mounted steering box forward of the 'H' beam on a bracket and in the NG's case the zero bump steer trailing arm rears.They were both changes that seemed to be a ' line in the sand' that changed they way new cars were built. 10 years also was a good even number. Around 1987 the first of the 'skinny' cars were built on mass with the Elfin Crusader, the Jabiru came around the same time also. Bringing a cut off or 31/12/85 for VB seemed to be another 10 year block but make another line in the sand and cut off the skinny cars form historic racing.
There probably is a need for a review to see if a VC is justified or not. It's 31 years ago now and those cars are more relative to historic racing then current. There have been rumblings that some HFVAA people may feel and introduction of VC would possibly devalue some of the VA cars. Of course convincing the Historic commission would be another thing as well.