Explainer: Engine and Aero Packages 2019-2021

Mix-and-match engine and aero packages were used from 2019-2021. Here’s what each one was and where it was used.

NASCAR has always used horsepower as a limiting variable. Horsepower limits speed, but also caps maximum engine rpm. Keeping engine speed below about 10,000 rpm lets engine builders use lower-cost materials instead of expensive alloys.

Although NASCAR started out using restrictor plates to limit speed, they later changed to tapered spacers. But even that wasn’t enough. So, in 2019, NASCAR turned to a second variable: downforce.

2019: Fixed Aero/High Downforce Everywhere

NASCAR instituted a high-downforce aero package with a big spoiler and splitter, and a sleek underbody.

  • Spoiler: 8” x 61”
  • Splitter: 2” overhang, 10.5” wings at splitter ends
  • Radiator pan: 37” in front tapered to 31” with vertical fences
  • Aero ducts: Used at majority of oval tracks larger than 1 mile

While the XFINITY series had long used a tapered spacer to tailor engine power output, the tapered spacer now came to the Cup Series. The Cup Series uses two sizes of tapered spacers:

  • 750 HP: 1.17” tapered spacer (for short tracks and road courses)
  • 550 HP: 0.922” tapered spacer (for oval tracks larger than 1 mile)

That gave us two fixed aero and three engine configurations: Taper550, Taper750 and Superspeedway. But since the 550Taper package could be run with (NA18D) or without (NA18D*) aeroducts, teams actually had four configurations to worry about. The table below shows and aero packages as columns and rows, respectively.

Aero packageTaper550Taper750SuperSpeedway
High downforce with aeroducts (NA18D)XX
High downforce without aeroducts (NA18D*)XX

Four is still less than one for each track.

2020: Fixing Short Tracks

The 2019 rules package worked well at the 1.5 mile and larger tracks, but not so well at the shorter tracks. Martinsville and Richmond, in particular, had lackluster races in 2019. Drivers and fans grumbled.

NASCAR needed more more variability. So in 2020, they introduced a second, lower-downforce aero package. This package featured smaller spoilers (2.75″) and splitters (1/4″ overhang), intended to emphasize handling and driver input. They christened this aero package ST/RC (Short Track/Road Course) because, well, it was used at tracks 1 mile and smaller. And at road courses.

Again, it seems like a small change, but each variation opens the door to spending more R&D money.

Hold on — I’m not going to count configurations yet because it gets even more complicated in 2021.

2021: Redefining ‘Short’ and Adding Dirt

In 2021, NASCAR opted to use the low-downforce package at tracks 1.3 miles and smaller (i.e. Darlington and Nashville). Although that doesn’t increase the number of configurations, they also added a dirt track, which necessitated a Taper750* engine package.

Engine and Aero Packages Summary

The table below sums up the engine and aero packages for tracks run in 2019-2020.

Track2019 HP2019 Aero2020 HP2020 Aero2020 HP2021 Aero
Auto Club550NA18D550NA18D  
Bristol (Dirt)750*ST/RC*
Charlotte ROVAL550NA18D*550ST/RC750ST/RC
COTA750NA18D* or ST/RC
Daytona RC750NA18D*
Indy RC750NA18D* or ST/RC
Las Vegas550NA18D550NA18D550NA18D
New Hampshire750NA18D*750ST/RC750ST/RC
Road America750NA18D* or ST/RC
Watkins Glen750NA18D*750ST/RC750ST/RC

At COTA, Daytona RC, Road America, and Indy RC, teams have the option of running NA18D* OR ST/RC.

Also: note that the 2019 Daytona 500 used the 2018 Daytona Rules Package.

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