Neptune

A live tuning tool for Forza Horizon 6 on PC.

Neptune connects to the running game and lets you change how your car behaves while you drive: torque delivery, boost, rev limit, ride height and the time of day.

Features

Tab	What it does
Engine	Reshape the torque curve by dragging it, set a torque multiplier and rev limit, and hold anti-lag on a key to build boost off the line.
Turbo	Boost ceiling, how much of that boost becomes power and torque, spool behaviour, synthetic lag and per-gear boost.
Suspension	Set ride height per axle, and drop the car on a key press with a smooth ramp.
Boost Gauge	A floating boost gauge on top of the game, as a dial, a digital readout or a bar.
Tunes	Save your engine and turbo setup per car and switch between saved tunes with one key while driving.
World	Change the time of day, and hold it there.
Presets	Save and reload whole setups.
Settings	Units, display and startup behaviour.

Anti-lag, air ride and tune switching can each be bound to a key or a controller button, on their own tab.

Download

Grab the latest Neptune.exe from the releases page.

Start the game and drive out into the world, then run Neptune. It needs to run as administrator to talk to the game, and will ask for that on launch.

Windows may warn about an unrecognised app, because the build is not code-signed. Each release ships a SHA256SUMS.txt you can check against.

Requirements

• Windows 10 or 11
• Forza Horizon 6 on PC (Steam or Microsoft Store)
• Python 3.11 or newer, if running from source

Running from source

pip install -r requirements.txt
python -m neptune.app

Run your terminal as administrator, or Neptune will not be able to attach.

Building a single executable

pip install pyinstaller
pyinstaller neptune.spec

The result is dist/Neptune.exe.

Where your data is kept

Tunes, presets and settings are written to a data folder next to the executable, so you can move the whole folder to another machine and keep them. If that location is not writable, Neptune falls back to %APPDATA%\Neptune.

The exact path is shown at the bottom of the Settings tab.

Notes

• Neptune reads and writes the game's memory only while you have it open. It makes no permanent changes to the game and installs nothing.
• Everything Neptune changes is put back when it closes. You can turn that off in Settings, and there is a Restore everything button at any time.

Project layout

neptune/
  core/      module contract, registry, runtime loop, settings, storage
  memory/    process access, address table, pattern scanning
  vehicle/   car discovery, identity and live state
  ui/        theme, shell, reusable widgets
  features/  one file per tab

Adding a feature is one file in features/ and one line in app.py.

Licence

GNU General Public License v3.0. See LICENSE.

If you distribute a modified version, or a build of it, you must also make the source of your changes available under the same licence.

Neptune is an unofficial, fan-made tool. It is not affiliated with, endorsed by, or connected to Playground Games, Turn 10 Studios, Xbox Game Studios or Microsoft. Forza and Forza Horizon are trademarks of Microsoft Corporation.