Its a long discussed flaw in the PI calculation to put it short. The stock 4 speed transmission in a lot of the muscle cars (and some classics) artificially limit to the top speed of the car keeping their PI low as on the imaginary track used to calculate it the long straights would hamper the car. The problem is these cars accelerate up to their relatively low top speed (129mph in B) well before any other cars will and due to the PI being lower than it should be you can also add a decent amount of handling to the car. What makes it obvious that this is the problem is that when you add a race gearbox to the car the PI will jump up to take it well into another class. So you have the acceleration and handling of a car around A590 in B class but with the low top speed. With the top speed being the limiting factor it becomes fairly pointless on all but the longest tracks. Even road america has the camaros at the top.
The '79 camaro is a lesser version of the cars that no longer post to the leaderboards due to this issue:
1968 Dodge Dart HEMI Super Stock
1970 Dodge Coronet Super Bee
1965 Alfa Romeo Giulia Sprint GTA Stradale
1967 Dodge Coronet W023
1964 Ford Fairlane Thunderbolt
1971 AMC Javelin-AMX
1992 Lancia Delta Integrale EV0
1969 Chevrolet Camaro Z28
There are a couple of other cars in the short circuits leaderboard because there are a few less straights for them to jump so far ahead.