Great info! I think I'm going to get started on blocking off my grill also. I just gotta find where I put the damn radiator fan. With the huge 2 core integra radiator in there, I don't have any overheating issues, even with the car idling for 15 minutes.
You have to remember that the above was calculated for that particular model of volvo, not every car. If your car has a small grille, you will not see that much benefit from blocking it.
For all we know, the volvo could have been this one:
[B]Grille blocking: 30% (allowing some holes for ventilation)
My take on the grill blocking thing:
1) you have to have some air flow thru the rad and around the engine to cool it...not very wise to block all flow
2) some of the mpg gain from this type mod probably has to do with increasing fuel and engine temps?
3) it's possible that extending the air dam down to the general ground clearance for the car would increase the vacuum pull thru the rad opening and help pull air thru the remaining openings under cruise conditions.
Leading the perpetually ignorant and uninformed into the light of scientific knowledge. Did I really say that?
a new policy....I intend to ignore the nescient...a waste of time and energy.