Can anyone offer some guidance for retrofitting floor-pan air deflectors on a 72?

I realize I need to drill 4 holes to attach each one, but do I need to tap the holes? Or do the screws go in from the top and thread in the plastic?

A good description would go a long way!

Tapping is not needed. They screw into the plastic. There are three holes in each flap.

Cary RIP did a nice detail on these when I offered a GB Post 81 http://www.914world.com/bbs2/index.php?sho...ctors&st=75

Just use through bolts with nylock nuts. Mark

I always wondered if a rubber air deflector all the way across the car would help with the airflow through the engine.....

Thanks, this was exactly what I needed to know!

Clay I also wondered about a full deflector. Maybe just where the deflectors are by the cylinder banks suck more air in from both sides and center to create more of a vortex of some kind cooling more?. But they work.

Here’s one way to look at this.

OEMs tend toward optimization. If you didn’t need them - they wouldn’t be there at all. If a full width deflector made a significant difference for engine temps or durability beyond the two that are there - it would probably be full width.

Easy enough to do back to back testing if you want to see experiment to see if it would affect engine cooling.

My modeling suggested that there is more airflow disruption using 2. 4 edges effectively.
This creates 2 low pressure areas. Mixes better than 1 unless you go down further. Not enough clearance to really do that. They made a really good design. The only improvement we could make was to add "winglets" on ours.