Originally Posted by
JeffYoung
Personally pet peeve of mine. I'm not sure (personally) why we don't publish the whole thing.
It's fairly simple actually:
Stock hp X expected IT gain in horsepower (25% is the default rate with the ability to move this up or down based on solid reliable evidence) X the Class Power to Weight Multiplier. There are then adders/subtractors of various types for suspension, torque and FWD.
So, say you have a 150 hp Schmorgwarp in ITS. It's a smogged up piece of crap and a good IT build gets you 35% gain. Process is:
150 hp X 1.35% X 12.9 (I think that is the ITS multiplier, would have to double check), which equals: 2612, rounded down to 2600 before any adders/subtractors. That's a fat Schmorgwarp.
But there you have it (essentially). If a car "straddles" a class, then we look to see in which class its race weight is most achievable given its curb weight.