One of the more confusing objectives in the Discover Japan campaign in Forza Horizon 6 is the Restrictor Plate challenge. A lot of players open the upgrade menu, search through engine parts, and assume the feature is missing or bugged. In reality, the restrictor plate is only available on certain racing engines and specific vehicle types.
If you are stuck trying to complete this objective, here’s the easiest way to unlock the upgrade and finish the challenge quickly.
Why the Restrictor Plate Does Not Appear
The biggest issue is that standard street cars do not normally support restrictor plates. If you load into the garage with a normal production vehicle, the Engine upgrade tab usually will not show the option at all.
To make the challenge work, you need either:
- A racecar with motorsport upgrades already installed
- A compatible engine swap
- A special campaign or DLC vehicle that supports racing regulations
Once you use the correct setup, the Restrictor Plate option appears in the Engine upgrades section automatically.
The Fastest Method – Mazda RX-7 Engine Swap
The most popular community method uses the Mazda RX-7 because it is affordable and easy to modify early in the game.
Here is the process:
- Enter any Horizon Festival site or player house.
- Open Garage.
- Select Upgrades & Tuning.
- Choose Custom Upgrade.
- Go to Conversion.
- Select Engine Swap.
- Install the 2.6L 4-Rotor engine.
- Return to the Engine upgrade section.
- Scroll all the way to the far-right upgrade categories.
- Install the Restrictor Plate.
After purchasing the upgrade and exiting the garage, the challenge should complete immediately.
Some players also report success using vehicles compatible with the 2.0L R3 swap, but the RX-7 and 4-Rotor combination seems to be the most reliable option so far.
Alternative Method – Use a Dedicated Racecar
If you already own rally or circuit racecars, this challenge becomes much easier.
Vehicles like the Subaru WRC Racecar already support restrictor plates through their stock racing engine setups. In these cars, you usually do not need an engine swap at all.
Just:
- Open Custom Upgrade
- Go into Engine upgrades
- Find the Restrictor Plate option
- Install it
This is probably the quickest overall method if you already have a proper race build in your garage.
DLC and Premium Edition Shortcut
Players with the Premium Edition have another easy shortcut available.
If you sort your garage by D Class vehicles, you may find the small Time Attack truck included in the DLC content. That vehicle reportedly comes with restrictor plate compatibility immediately available, saving time and credits on engine conversions.
It is a niche option, but useful if you already own the extra content.
Campaign Progression Method
Another solution is simply progressing through the Discover Japan storyline and unlocking more Barn Finds.
One hidden Barn Find vehicle is apparently designed around racing regulations and already supports restrictor plate upgrades. If you are planning to continue the campaign anyway, you may eventually unlock a qualifying car naturally without spending extra credits.
Where to Find the Restrictor Plate Upgrade
A lot of players miss the part because it is located near the far end of the Engine upgrade categories.
After installing the correct engine or using a compatible racecar:
- Open Engine upgrades
- Scroll completely to the right
- Look for Restrictor Plate
- Purchase and install it
The challenge trigger usually activates the moment you leave the garage.
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