Originally Posted by EH3
over the 104.6 miles i drove today i filled up with 2.40gals.... 43.6mpg w/o the gill block! WTF? that's a HUGE difference from the 38.2mpg tank previously. could it really be hurting my aero that bad by having it on?
Grill blocking is clearly a balancing act. If you do too much grill blocking FE does go down. But that lower FE is not due to aero (the best aerodynamics really are with a full block), but rather the heat (which increases, the more grill blocking you do).
If the engine gets hot enough, the cooling fan(s) come on (to cool down the engine, and keep it from overheating), vs you lucking out and getting the cooling by the air going through the grill. And those fans use a LOT of power, and therefore have a surprisingly high drag on the engine (often much higher drag, than the drag savings from doing the grill block in the first place). And worse yet, if/when the engine gets "too hot", the ECU might sense something wrong, and convert to "limp home" (fuel wasting) mode, to try to get you home safely. And both of these things can cause your FE to go back down...
BTW: On my CRX an aprox 2/3 grill block (the left and right sides blocked, but the center left open) seems to be about where the sweet spot (best FE) lies. No doubt the sweet spot will be different on other cars, so YMMV (and you might have to experiment). But the point is, some grill block can often improve FE, but "too much" can actually cause you to lose FE...