Program.cs

using ForzaUdpMock;
using System.Net;
using System.Net.Sockets;

string targetIp = "127.0.0.1";
int targetPort = 5300;
int hz = 60;
int engineMaxRpm = 10_000;

for (int i = 0; i < args.Length; i++)
{
    switch (args[i])
    {
        case "--ip" when i + 1 < args.Length:
            targetIp = args[++i];
            break;
        case "--port" when i + 1 < args.Length:
            targetPort = int.Parse(args[++i]);
            break;
        case "--hz" when i + 1 < args.Length:
            hz = int.Parse(args[++i]);
            break;
        case "--max-rpm" when i + 1 < args.Length:
            engineMaxRpm = int.Parse(args[++i]);
            break;
    }
}

var baseMessage = new Message
{
    Game = EGame.FH4,
    EngineMaxRpm = engineMaxRpm,
    EngineIdleRpm = 1_000,
    IsRaceOn = 1,
};

var endpoint = new IPEndPoint(IPAddress.Parse(targetIp), targetPort);
using var udpClient = new UdpClient();
var cts = new CancellationTokenSource();

var senderTask = Task.Run(async () =>
{
    using var timer = new PeriodicTimer(TimeSpan.FromSeconds(1.0 / hz));
    try
    {
        while (await timer.WaitForNextTickAsync(cts.Token))
        {
            byte[] packet;
            lock (baseMessage)
            {
                packet = baseMessage.GetPacket();
            }
            await udpClient.SendAsync(packet, endpoint, cts.Token);
        }
    }
    catch (OperationCanceledException) { }
});

Console.WriteLine($"Sending FH4 packets to {targetIp}:{targetPort} at {hz} Hz.");
Console.WriteLine("Type an RPM value and press Enter, or 'q' to quit.");

while (true)
{
    string? line = Console.ReadLine();
    if (line == null || line.Equals("q", StringComparison.OrdinalIgnoreCase))
        break;
    if (float.TryParse(line, out float rpm))
    {
        lock (baseMessage)
        {
            baseMessage.CurrentEngineRpm = rpm;
        }
        Console.WriteLine($"CurrentEngineRpm => {rpm}");
    }
}

cts.Cancel();
await senderTask;