Completing the Discover Japan Collection Journal in Forza Horizon 6 requires navigating a massive list of 47 unique car upgrades. Among these, the "Restrictor Plate" modification often leaves players scratching their heads. If you are browsing through the upgrade menus of your favorite sports cars and finding the option completely missing, you aren't alone.

Standard production road cars do not feature restrictor plate options on their stock engines. To install or remove a restrictor plate and check this elusive upgrade off your list, you must use a dedicated racecar or utilize specific racing engine swaps.

Here is exactly how to unlock the restrictor plate category and finish your 47/47 upgrade collection.

The Easiest Ways to Get a Restrictor Plate Upgrade

You can quickly cross this milestone off your journal using one of two highly reliable methods.

Method 1: The 1.6L I4 Turbo Rally Engine Swap

This is perhaps the most straightforward approach if you have unlocked a few specific vehicles in the game.

1. Get the Car: Obtain a car like the Honda HSX-R GT (which can be easily acquired as a Barn Find during your playthrough).
2. Swap the Engine: Drive to any Horizon Festival Site or Player House. Go to the Custom Upgrade menu and navigate to Conversions > Engine Swaps. Purchase and install the 1.6L I4 Turbo Rally engine.
3. Toggle the Plate: Go back to the main Engine Upgrades tab. You will now see a newly unlocked Restrictor Plate category. Select it and change the setting—for example, switching it to "No Restrictor Plate."

Method 2: The 2.0L R3 or Racing 4-Rotor Swap

If you prefer classic Japanese tuning legends, you can utilize high-end racing engine conversions.

1. Get the Car: Purchase a standard Mazda RX-7 (such as the Spirit R or Type R) from the Autoshow or your garage.
2. Swap the Engine: Enter the Conversions > Engine Swaps menu and select the Racing 4-Rotor engine (typically found in the upper-left of your conversion options). Alternatively, you can use any compatible vehicle that supports the 2.0L R3 racing engine swap.
3. Toggle the Plate: Head back into the Engine upgrade tree, open the Restrictor Plate tile, and buy the modification to trigger the journal entry.

Remove Restrictor Plate

Upgrading your engine and hunting down rare Barn Finds to unlock these restrictor plates can get expensive quickly, especially when you are trying to complete the entire Discover Japan Collection Journal. If you find yourself running low on in-game funds for these high-end engine swaps, you can easily stock up on cheap Forza Horizon 6 credits at SHANNENG. Getting a quick boost from SHANNENG ensures you have more than enough cash to buy the Mazda RX-7, pay for the expensive 4-Rotor conversions, and experiment with any other build you need without grinding for hours.

Which Cars Have Restrictor Plates in Forza Horizon 6?

If you want to skip the engine swap process entirely, you need to drive a car that features a restrictor plate natively on its factory motor. These are exclusively purpose-built racing vehicles designed to mimic real-world motorsport balance-of-performance (BOP) regulations.

Look for the following vehicles in your garage or the Autoshow:

• Dedicated GT Racecars: Purpose-built track machines and factory GT cars have adjustable restrictor plates right out of the box.
• Formula Drift Cars: The vast majority of the Formula Drift lineup features open engine setups that support immediate restrictor plate modification.
• Subaru WRC Racecar: This legendary rally model features an adjustable restrictor plate directly attached to its stock rally powerplant.
• Time Attack Truck: For players who own the Forza Horizon 6 Premium Edition, the small D-class time attack truck comes with an adjustable restrictor plate that can be tuned immediately.
• Honda HSX-R GT: As mentioned above, this Barn Find is a prime candidate for a quick rally swap to trigger the upgrade path.

By focusing on these specific racecars or utilizing the 1.6L Rally and 4-Rotor swaps, you will instantly unlock the restrictor plate tile, allowing you to easily complete your Discover Japan Collection Journal.