After reading the previous discussion on the rumored 8:02 M3 time, and the recent discussion on the 7:38 GT-R time, I did a regression analysis for weight/power vs. ring laptimes. You'll see the cars that were included in the spreadsheet. The redline in the graph is the best fit line, which is:
Time=422.15 + 15.95 * Weight/Power
Adjusted R^2: 0.78
These numbers basically mean that a significant linear relationship, as described by the above formula, exists.
The crank power and weight figures were taken from supercars.net. I don't have a position on their accuracy; just plotting some of what's on that page.
If we can build a database for known wheel dyno numbers, I can re-run the regression.
It would be interesting to discuss the cars that don't fit the trend.