Grill Block Summary

[gascort]

Good post to the OP. Regarding the duct, I would make it the same size at the radiator as it is in the front. Mine constricts too much at the radiator and yesterday I had to cut a hole in the top of my block that is very nasty for aero. ;( needed the car to not overheat and to have AC for the family.

[TheEnemy]

Originally Posted by comptiger5000

Unfortunately, this is one mod I could never try safely with my Jeep. It would get way too hot with the 360 under the hood. They had to change the grille design and add heat extractor vents just to keep it cool with the bigger engine.

In the 102* weather yesterday, it was running about 205* on the highway at 60mph, and just under 210* around town (e-fan on low due to A/C system pressure). It hit 210* a couple times driving up hills in town. I wouldn't want to reduce airflow in this thing, at least not in the summer.

You might look for places to put vents to let air out of the engine compartment. The stock grill will let lots of air in, but often there is no place for it to go after its in the engine compartment.

Here in New Mexico we get 100+ pretty regular, many of the Jeeps that get used have vents cut into the hoods, just to let the hot air out.

[comptiger5000]

Being a 5.9 Limited, it actually has vents in the hood to let the heat out from the factory. It keeps itself cool enough in stock form, but not with much room for error.

EDIT: Fixed the picture

You can see the vents in this pic:

[TheEnemy]

Originally Posted by comptiger5000

Being a 5.9 Limited, it actually has vents in the hood to let the heat out from the factory. It keeps itself cool enough in stock form, but not with much room for error.

You can see the vents in this pic:

The pic didn't show, but as far as Jeep cooling having not much room for error seems to be standard on any model.

[QuickLTD]

grand cherokee hood vents - Google Search

And a page with temperature info that is vehicle specific
Hood Vents

[comptiger5000]

That's almost exactly where my hood vents sit, although mine are the factory ones referenced in the link as coming only on the 5.9. That thing puts out A LOT of heat.

[Frank Lee]

Oh that's why they are so efficient.

[comptiger5000]

Exactly. It's not a terribly efficient engine (but the 4.0 I6 is no better, just has the advantage of less displacement), and it's in an inefficient vehicle. That's why my focus is on engine mods first, aeromods later. I figure I can gain 2-3 mpg on the highway just from improving engine efficiency a bit.

In my drive cycle, the 4.0 in Mom's Jeep (year newer, 2nd generation, but same weight, similar CDa) gets about 0.5 mpg better around town, and about 1 mpg better highway. At that point, I figured why not get the V8, especially considering the I6 tranny is a bit undersized, and tends to fail if not maintained perfectly.

[4536]

[QUOTE=texanidiot25;182669]How is the upper grille closer to the ground?

Sorry for the confusion. With the upper grille blocked the lower grille is still in operation and "it" picks up warmer air coming off the pavement than the upper grille did.

[comptiger5000]

I was thinking about this today. Would trying to increase airflow through my hood vents improve aero somewhat (in lieu of a grill block), as more of the air entering the grille would be able to pass through and exit cleanly, rather than packing up and bouncing back out?

I might try spacing the drip trays on the vents down a little this afternoon to see if I can get more air out through there.