Performance Adjustment:  
Each car will be subject to a PI adjustment, however large or small.  Each decision is final, made by me and/or another moderator of my choice.  I will do my best to make an equal playing field and to keep myself in check when making these PI adjustment decisions.  

Builds:
Each car has a specified PI level.  For the vast majority of the eligible race chassis, this means that only tire width adjustments and rim changes can be done.  As a result, there can be NO REMOVING OF RESTRICTORS on race cars, except for GT2-class chassis competing in Super GT.  However, for all street cars in GT and below, there is no specified build.  there are some restrictions on what each car must have, regardless of class:

Required Parts:
--Race tires
--Full roll cage
--Full adjustable aero
--Race brakes
--Race suspension

Limitations:
Aside from each car being suject to a PI requirement, there are power limits for each class:

Super GT:
All GT1 ('90s and '00s), GTS, DTM, and GT500 race cars, the Ferrari FXX, the Ferrari F50GT, and the Pagani Zonda R are limited to stock power.
The upgraded GT2 cars have maximum power on their original engines.

GT:
All race cars are limited to stock power.
--This may be subject to change, as the GT300 cars are a bit down on power.


Supersport:
GT4-bucket cars are limited to 600HP.
Unlimited-bucket cars are limited to 550HP.

Sport:
Base PI is AWD 510, RWD 520, FWD 530.
All cars limited to 450HP.
SEAT Leon Supercup  533 PI (static PI).

For more information about each class' PI requirements, see Car Specs.  But this should be all you need.

--Edits: Included Supersport and Sport, finalized race car PI, horsepower limits, and required parts.

GT and Supersport road car requirements back under testing and revision.