After I copied all cars specifications from Edmunds into Excel format, I analyzed it to show you how American cars evolved over past 30 years. I calculated using AVERAGEIFS formulas, breakdown by domestic and imported cars. Charts made at 22 September 2019 update with 58480 cars (model trims). You can buy Excel database: Year-Make-Model-Trim-Specs.
For example average engine size rose from 3.33 L in 1990 to 4.09 L in 2007 then dropped to 3.36 L in 2019 due to introduction of turbochargers that allowed downsizing engines, meantime horsepower rose from 142 HP in 1990 to 294 HP in 2019. In 2019 domestic cars averaged 316 HP vs imported cars 279 HP. Cars also grew in terms of external dimensions, but the increase in weight was most significant.
Note: because most manufacturers launch 2020 SUVs and trucks later than small cars, the averages for 2020 Model Year appears smaller than previous years.