On March 18, 2019, senior environmental artist Josh Andersen released several images on ArtStation detailing some cars he had worked on. A number of these cars later either made it to Forza Motorsport 7's DLC packs, Forza Horizon 4, or Horizon 5, or were just left on the cutting room floor.
Andersen explains:
These will be some of the cars I worked on Turn10's car art team for the most recent Forza titles. I didn't create them, for the most part, though I did create some of the content as needed. I was part of a team responsible for bringing them up to the last 10%. Fixing bugs, getting content attached to gameplay mechanics, mostly technical details, but tuning the lights, adjusting shaders, setting attributes, generating masks, animating the parts than needed motion, was involved. *They will be uploaded as they are approved*
It appears that Andersen later went back and deleted a number of images from his post along with censoring the debug menu on others, but reuploads can be found on GTPlanet. The author comments unfortunately seem to be lost.
Below is a gallery of these cars. Author comments are marked in italics.
1929 Mercedes-Benz SSK Roadster. Debuted in FH4 on the Car Pass on January 24, 2019. Mercedes 1912 SSK.[sic]I had to do a fair amount of updates on this, including recreating the fenders to the manufacturer's desires. A lot goes into these, from tuning the lights with the glass, optimizing, skinning and weighting the bones for vibration.1970 Porsche #3 917 LH. Debuted in FH4 in Update 13 on August 28, 2019.2017 Aston Martin Vanquish Zagato. Debuted in FH4 in Update 12 on July 30, 2019.2004 Nissan #23 Pickup Rally Raid. Debuted in FH5 at launch.2018 McLaren Senna. Debuted in FH4 at launch. Ferrari Superfast 812.[sic]This, I think, was my favorite. Had to do some research on it to get the feel right, how it ran on the Autobahn. Tuning the visual features, while the engineering team dealt with the handling.2017 Volkswagen #34 Andretti Rallycross Beetle. Debuted in FH4 at launch. This would've made me laugh, but it's just plastered with so much sponsorship, there's gotta be something to it, right? It's like Herbie The Lovebug," Gone all Hollywood. Though... no doubt it's souped up like crazy, to trick the unsuspecting.1963 Shelby Monaco King Cobra. Debuted in FM7 in the Barrett-Jackson Car Pack on January 15, 2019. Well... this was about when style was equal in importance to performance. Not that it isn't still, but this was at the extreme end of both.BMW #1 BMW M Motorsport M8 GTE. Debuted in FM7 as a free Spotlight car in the December 4, 2018 update. BMW M3 Touring.[sic]Oooh! I loved this one. Look at those lines! I went over this a bunch of times trying to bring it to perfection.Hoonigan Gymkhana 10 Ford Fiesta ST. Debuted in FH4 in Update Three on November 22, 2018. Love this puppy! So much character! Had to make a few fixes on it, as far as getting it to work in-game. Shader changes, damage adjustments, so parts didn't clip through parts. There's a lot more to it, especially interiors, but, that's part of it.2011 #5 Ford Performance Racing FG Falcon. Last seen in FM5. These cars, with all the sponsor decals. Difficulty here, was, there's the main paint job, then there are the overlay decals, which had to be lined up, so that when damage occurred, the decals bent with the body, at all LOD levels. That, and alpha sorting2013 Honda #9 Target Chip Ganassi Dallara DW12 (with incomplete livery). Last seen in FM5. Indy cars, these were tricky to get to work correctly. They didn't have all the seating , but the livery the optimizations, aligning things precisely was a bit of a chore, but they look great on the track!