So... if you're trying to keep the total HP below 510... use either a calculator and figure the multiplier against HP of motor working with to achieve that and set it in the config file in section [1_Other] on line;
engineTorqueMod=

For example, if you had an engine that only was 360 HP (stock measurements ofc) and you wanted to increase it to 510 (approx.) then you'd put (instead of the default 1) a 1.4 for the value. If the HP of the stock motor were too high to begin with, you'd put in (for example a 630 HP motor) would be 0.8.

You can also do this in Car Editor and the little info window that pops up when you're in that same category adjusting this number will show what the HP calculation is. It's actually recommended that you make a custom config file / sub-model of whichever cars you want to adjust these types of things. This way the user created config files will not get tampered with by the game / steam should you need to do file verification or updates made to game.

Edit: Just don't forget to put a unique identifier in the 'Suffix=___' line so the game can differentiate between model versions. Has to be different that any other configs for that car.

Thank you so much! this worked beautifully.