Its not a straight path though... It has to squeeze through the radiator and a/c coils, then it hits the fan, then it hits the engine and forces its way through and then its under the car (which on most vehicles isn't very aero-friendly). Grille blocking keeps the air on the body of the vehicle where the body design is made to deal with it, and a side benefit is that the vehicle warms up faster and usually has higher intake air temps which both help economy.
Yeah it's not a straight path, but it's not like hitting a panel and going around is a straight path.
Also, the fan isn't an obstacle if it's spinning and pulling the air.A flat surface perpendicular to the airflow is going to create a lot of air resistance, but air being sucked into a vent is creating negative air resistance.
Air going through the radiator is also fulfilling a purpose.
What I really don't understand is blocking grills from the back. How can that possibly create less air resistance than the air going into the vent, most of it continuing through, and some of it being pushed back out the front?
Take a mesh window and push it through the air-- some air resistance. Now cover the back with paper... more air resistance, not less.
bowtieguy linked to a great explanation in post 11 of this thread...
Yeah, I get the cone of air thing, but if you're arguing that the radiator presents too much resistance to flow, doesn't it stand to reason that the radiator contributes to creating a cone? The less the radiator and internals block air and create a cone, the less resistance they create and the more flow they allow, so it would be a break-even kind of thing
It really depends on the vehicle. Take my truck for example. It has a huge grille of several square feet. I restricted it down ~95%. The truck coasts farther now, and warms up quicker. Both things good for FE.
The outside of the car, except for the underside, is the only part designed to flow air well. Therefore, it makes sense to try to direct air to that area.
Grille blocking is intended for more than just aerodynamic purposes, though. It is used to increase the temperature under the hood, decrease warmup time, and possibly increase intake air temperature. Somewhere among at least one of those possible advantages, or maybe some other unknown advantage, is the cause of the consistent results that some people get. Enough people get enough consistent results and back it up with enough data that it's hard to believe.
Still, it's good to question why it works and try to figure it out, and if you still don't agree, to continue to chase it until it's figured out or we all get tired of it.
Well, since about 1 month ago, I've had the top grill block installed on this car. I haven't gotten around to putting up photos though (all you have to do is imagine blue and white coroplast on top of the black grill).
In terms of results, maybe take a look at my gaslog. It looks like I get a little boost, but I've been doing considerably more highway driving than before. I have noticed, however, that my water temp has been much higher. It used to go only up to about 186 degrees F, but now I've seen it go as high as 210.
That being said, I plan on taking off my grill block over the weekend. Why? To see if its actually doing anything. After 3 weeks of driving the same route and getting about 37mpg consistently per tank, I'd like to see what its like without a grill block. Plus, its ugly as hell and I think I can make a much nicer looking one.
Well, I just filled up my tank after having NO grill block on. The past 4 weeks I've been driving mostly highway and I've had plenty of time to use hypermiling techniques. My gaslog seems to show 37mpg for the weeks I used the grill block except the last fillup, where I got 38.7mpg (the highest I've ever reached). With no grill block, I got 38.5mpg.
So is a grill block for the 2003 Lancer worthless? I wouldn't say so. I noticed on a calibrated SG, going 80mph with grill block gave me a sustained 33mpg. Without the grill block, I'd get somewhere around 31mpg. If anything, this evidence suggests that hypermiling techniques such as drafting, P&G and DFCO may have a greater impact on fuel economy than relying on a grill block alone.
However, the grill block was extremely ugly. I've never driven a car that turned so many heads.