So I managed to get 2 AcceleRacers prototypes by now (the other one being Reverb). But this one actually has some interesting differences when compared to the regular release, so I decided to document this info.
I didn't include the raw ZAMAC blank base or the Barbie plastic on the list because all AcceleRacers protos share those features.
1 - Different grill: RD-09 has a nicely detailed grill, but it looks like that was a late addition to the car, as the prototype has a more simple, less detailed one.
2 - Sunken flame logo:As a First Shot prototype, the purpose of this car was to test fitting and scaling between its parts. This one was clearly a failure, as the interior piece is smaller than the rest of the car. This caused the flame logo to be sunken on the base instead of aligned with it like the in regular cars It is not smaller than the regular fire decoration though (probably scaling issues).
3 - Sunken and smaller rear plastic: This is caused by the same issue as the previous difference, the rear plastic details look smaller because the plastic part itself is smaller.
4 - Smaller front engine AND front engine hole: The engine itself shares the issue of the 2 previous differences, but this case is a little different. Though the engine itself is just slightly smaller, the hole in the body which fits the engine is considerably smaller. This gives us the illusion of an even smaller front engine when compared ot the regular car.
5 - Bigger and smoother side vent: Honestly I don't know why this vent even exists, as it's not present on any concept versions of the car and even Mainframe didn't include it in their animation model. Anyway, this prototype has an even bigger vent, and it also has smoother edges. A friend said it might look bigger because the car it not painted, but I compared it to the Ultimate Track Pack RD-09 (which doesn't have a painted body) and the prototype vent still looks bigger.
6 - CM5 wheels: Most people know early AcceleRacers cars were featured with CM5 wheels instead of CM6s. Some cars like Synkro only appeared with CM5s in promotional pictures, but some of them actually made it to wave 1 of the AcceleRacers toyline, like Nitrium, Iridium, RD-06 and some Metal Maniacs. RD-09 wasn't the case, it was never produced with that wheel type. Yet the prototype has a full set of CM5 wheels. It's interesting to note that the rear wheel on the picture is actually an error, it has some plastic flashing on it.
7 - Misaligned windshield: Looks like the mold for the prototype window piece wasn't all that good, as it barely aligns with the car body (leaving some openings on the sides from where I can see the interior). It also has a code engraved on it which reads "G8115-2419-2".
G8115 is the actual car code, 2419 is unknown, and the number 2 is present on all pieces of the regular RD-09 I drilled into, so my guess is that it's maybe the version of the car (being G8115-1 a rejected version, which makes sense as this car is quite different from Dwayne Vance's original concepts).
Thanks, pretty much it, enjoy!