Noob homoligation question

In free play i want to race forza gt class cars with now restrictions. After i select forza gt and change PI and horsepower to any, it changes my car class to any and vice versa and i end up racing against highed end P cars. Is there any right way to race with only one division of cars but no restrictions on car upgrades?

In the prior games i could mod up a and old muscle car and see how well it can hang with newer cars. Why is the homoligation so restrictive in offline free play?

As soon as you choose a car homologation class(in your example forza GT), you have rules/limits that cant be broken. max Tire width, max tire compound, PI limit, max HP, possibly others…as soon as you start changing the other settings that are outside the homologation rules, you’re not in Forza GT class anymore.