mitdr774, clean looking grille blocker! Much nicer than my hack job...
Last winter I tried to test the mpg effect of the upper grille blocker. It's really tough to accurately/consistently test a very small 1-2% improvement.
http://www.sonicownersforum.com/forum/t1032/ post #10
Doing a back-to-back, using the cruise control resume to make sure the tests are at the same speed. I got a 0.6 mpg improvement... (recently people have noticed CC resume speed creep up, so that may be a problem)
Testing over a full tank introduces all kinds of variables, temperature changes, average speeds, traffic changes, could vary significantly...
Last year I was worried about blocking the lower grille because of the I/C. But I was thinking, many older turbo cars never even had an I/C, and I rarely go over 3-4 psi boost anyway. If the intake air does get too hot because of the I/C being blocked, the engine computer will do what it needs to do to protect teh engine.
So this winter I have the lower grille 100% blocked off with duct tape. The upper grille blocker has a 1.5" x 5" hole in the lower center.
Right now, I'm doing the 93 vs. 87 test for myself. I just got thru 4 tanks of 93, now running 87, I'll see if I can back up what people have said about 93 paying for itself with 2-3 mpg gain...