Doing all the work yourself?
I have a way for people to report DIY repairs. But I haven't yet implemented a way to include heavily modified cars. In the future, I plan to analyse the powertrain, chassis, and rest of the car separately. Modded cars might just be included in the third analysis. But I'm not doing this yet.
Mods I have no problem with at this pont:
--intake, exhaust, other mods that add at most 25 horsepower total
--wheels up to an inch larger than the largest stock wheels on the model
--springs/struts that lower the car up to an inch
Vehicle reliability, price comparisons, fuel economy