Glenn, The allowable is based on the year and weight of the car.I haven't had a 1980 anything tested in years but my 1985 626 is allowed 1.21% CO , 189 HC,1374 NOx@25/25 and 1.10 CO,194 HC,and 1504 NOx@50/[...] far as an underhood check it is just a glance to ... Login to read more.