These are the best quotes I can find that people have found in the proposed legislature, this is a huge document to go through.

Quote:
EPA is proposing in 40 CFR 1037.601(a)(3) to clarify that the Clean Air Act does not allow any person to disable, remove, or render inoperative (i.e., tamper with) emission controls on a certified motor vehicle for purposes of competition.


and

Quote:
Certified motor vehicles and motor vehicle engines and their emission control devices must remain in their certified configuration even if they are used solely for competition or if they become nonroad vehicles or engines”. 80 Fed. Reg. 40138, 40565 (July 13, 2015).


Wouldn't this still allow you to race a non emissions certified car? and possibly a purpose built car like a pro mod or a dragster?

I would guess that they are attacking chips and cat removal mods.