Yeah, the GNX was reportedly underrated on horsepower figures.
Officially, Buick claims a 0-60 mph time of 5.4 sec for the GNX versus their Grand National number of 6.9. Through the quarter mile, the GNX clocks 13.4 sec to 104.0 mph against 15.7 at 97.5.Sep 5, 2016
That was fast for the era.