After I copied all cars specifications from Edmunds into Excel format (you can buy full Excel database: Year-Make-Model-Trim-Specs) I analyzed it to show you how American cars evolved over past 30 years. I calculated using AVERAGEIFS formulas, breakdown by domestic and imported car model trims available for sale, NOT based on number of cars sold, low-production high-powered cars inflated horsepower figures.
For example average engine size rose from 3.33 L in 1990 to 4.09 L in 2007 then dropped to 3.42 L in 2020 due to introduction of turbochargers that allowed downsizing engines, meantime horsepower rose from 142 HP in 1990 to 299 HP in 2020. In 2019 domestic cars averaged 333 HP vs imported cars 282 HP. Cars also grew in terms of external dimensions, but the increase in weight was most significant because more and more SUV models came on market, which also need more power.
Charts based on 13 August 2020 update with 60414 cars (model trims).
Note: there are only 345 “2021 models” included, compared with 2843 “2020 models” thus 2021 figures are not relevant. Most manufacturers launch SUVs and trucks later than small cars, the averages for 2021 Model Year appears smaller than previous years.
Before current upwards trend, there was a downwards trend from mid-1970s to mid-1980 when most American domestic cars were reduced in dimensions and engine size (and possible horsepower was also reduced at smaller extent) because of 1973 and 1979 oil crisis, but I haven’t found reliable data with specifications for cars produced before 1990 to make an analysis on.
The 1970s oil crisis are also the reason for which smaller and more fuel efficient imported cars gained marketshare (before 1970s even if number of distinct imported models was similar with number of distinct domestic models, 90% of cars sold in US were domestic made).