[Daschicken]

Having experience grille blocking 2 different accords, i've got some info for you.

Previously I had a 2005 4 cylinder 5mt, I could block MOST of the bottom grille, but not entirely or it would start to overheat. I don't remember which temperatures were too hot for it. Never tried an upper grille block on that car.

With my current 2006 V6 6mt I usually run a 60-70% lower grille block. Above 85 degrees and the fan kicks on a lot. When it drops below 50 degrees I can run a partial upper grille block, usually blocking half of the upper grille.

If you are willing, I strongly recommend pulling off the front bumper and making a panel to ensure the incoming airflow going to the lower grille does not bypass the radiator by going underneath it. I did this and a partially ducted grille block and was able to make the opening smaller while keeping the same cooling capacity, if not better.


Rear window spoiler: Absolutely not, you will only increase the drag.
Trunk lid spoiler: If you can get one for cheap/make one then you should consider it. This is something that will likely not pay itself back unless you DIY.


A full undertray will definitely be worthwhile as far as aero goes, but it is a lot of work. I've got a mostly full undertray on my car and it definitely improves coasting, as well as high speed stability.