Gator, I think you are right about other weights... most of them are not fully completed cars.

Also, I have a full tank of gas, full fluids (including all the stuff for the oil cooler). The AWIC is full of water, using 3/4" hoses, and my remote oil cooler with hoses is also full of oil.

Another thought is the exhaust manifold. Mine is stock. Guessing some are running headers which are somewhat lighter. Also full size battery.

Some thoughts on R vs S is that the S windshield adds a lot of weight. Not sure if it's more than the added frame structure on the R though. I have all the R aero except the diffuser and rear wing which I don't think add that much weight. Maybe 10-20 lbs?

Would really like to see more weights that are all-up, with driver in the car, all fluids in, ready to hit the track. Guessing most of these weights would come up quite a bit.