Old Mech, when I saw the pipe foam to block off, it was a DUH! that is brillant idea.
My air dam was scrap from a neighbor, I just had to buy the self drilling screws. The other neighbor had a roof put on and they left a scrap of flashing that I used to block the grill. I used more of the screws from before...and I painted it flat black since is was bright silver.
What also was not seen is I used a piece of roll up sled put out for garbage to further block the radiator. I would us it to adjust for ambient temps even after the grill block.
Not only did I see MPG gains, but I was also drag racing as well on some Friday nights. Just dropping the rear bumper cover, aka the parachute dropped .3 seconds off the mid 15 second ET. I later trimmed a bumper cover for ok looks without the parachute effect.
The idea about the bumper was inspired by someone posting a underside picture of the VX deflector piece Honda installed from the factory.
Jason "Katman" took the picture....