The only Direct Drive Vehicles that I know of are the Dirt track cars like the Midget class cars.
These cars need to be pushed by a truck to start their motors due to the direct drive. These cars will stall out if they come to a stop, not having a transmission.
The vehicles run different tire sizes at all four corners in or to help them turn.
Vehicle speeds are limited since it's direct drive, you can only turn the rear wheels as fast as the engine's redline.
In your case it would be best to swap a manual transmission in your neon in order to gain more FE. You could also try adjusting driving styles and techniques and see if you're happy with the results.
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