When is 300hp not 300hp? In the A Spec Expert Schwarzwald league of course!
You need to be able access the Expert level in A-Spec mode, so a minimum level of 15, not too difficult. Its a German only race which allows German cars with a maximum of 300hp. I just entered it with my worked 600bhp C63 AMG beast.
You can pretty much enter any German car! Joel Kesseboom from the GT5 cheats forum was the person who told me about this. You can check out the thread here. He entered the race with an Audi R8 and others have entered with a Mercedes SLS Stealth car and just destroyed.
Super easy to win and a great way to make a cool 25k without breaking a sweat. So grab your favourite German car, work it up (or not) and make some easy money winning races and trying out your overpowered machine.
What ridiculous car have you entered?