[Rob. Smith]

It's a while back now but I had to perform a stationary test as well as a drive-by (in two directions) in second gear accelerating. My car passed engine bay noise but struggled with exhaust (temporary under car . exit on rh side system) the exhaust was too quiet..it whistled and freaked out the sound meters on the rh pass. creative averaging made the paperwork look good.
As far as engine noise I've seen one bloke temporarily line the engine bay with high density foam (black sponge like) to keep the noise down. it worked...there was much care taken to avoid hot bits. All wired and taped back to be held in place for a short time . I think it was glued to light ply or heavy cardboard to do the job.