Less drag (plugging the grill)

[bnther36]

I was contemplating setting some plugs back in behind the grill with the intention of making the nose of the car more aerodynamic and maybe give my mileage a boost. I am familiar with aircraft composites so making something light and form fitting will not be a problem. What I am wondering is whether it would be better to plug the bottom most scoop (below the bumper) or the the upper part. Which one has the most effect on cooling? Which one would have the most effect on drag?

[Yarii]

Generally speaking, plugging the upper end of the grill has a slightly greater aero advantage because it helps maintain laminar flow over the hood of the car.

Depending on your climate and the kind of driving you normally do, you can get away with plugging more than you might think. I've seen old Honda DeSol's with a 3X4" rectangle left open that still run at normal temperatures. Just watch your temps (Does a scangauge tell you coolant temperature?) and wherever you find the tipping point between normal city stop/start driving and overheating, open up a bit more than that as a safety.

Just so you're aware, I have no idea what this does to your transmission cooling or air-con efficiency; Probably nothing good, but your mileage should increase measureably.

[Spades]

meh, my car gets 35+ MPG in the city with me flogging it. with the way I drive it I would rather not risk overheating the engine or transmission in the name of 1mpg...maybe if this was a truck getting 5mpg-15mpg, but at 30+ who really cares?

[joey1320]

if i was you i would start with a full underbody panel and see what happens.
then you don't sacrifice the engine wear/cooling.

[Yarii]

Originally Posted by joey1320

if i was you i would start with a full underbody panel and see what happens.
then you don't sacrifice the engine wear/cooling.

Underbody panel is also a good idea, but expensive, and has a possibly worse heat issue around the exhaust if it's not properly designed...

You have to remember, cars are designed to endure stop and go driving in an Arizona summer heatwave. As long as the engine still has enough airflow to remain at it's operating temp, the only concern I'd have is with transmission cooling, and I think that's more of an issue with the automatic. As I recall they generally operate around 90C. You can get a good add-on tranny cooler for like $40 to make sure you're not getting the fluid temps too high.

A guy living in Michigan could plug off most of the grill all winter without worrying about damaging the car - Summertime I imagine you'd have to, or at least should, open up some more cooling space.