Hood louvers and hood scoops

[warrpath4x4]

my XJ had heat issues even after a bigger radiator and other things, i believe in function over form so i found some cheap soffet vents for a house at home depot for about $3 each. dropped my engine temps by 10 degrees at all speeds and idle, these have a mesh screen built in to keep leaves out, i just used a hole saw and put some holes in under them instead of cutting the whole piece out.

[LaOutbackTrail]

I went out to the truck last night to ponder the louver idea. The hood will not be an issue, but going through the fender won't be possible on my montero. Too much crap bolted to the inner fenders and between the inner and outer fenders.

I'm considering using one of these options:
http://www.quadratec.com/products/12124_034X_PG.htm
http://www.quadratec.com/products/12124_035X_PG.htm

[etbadger]

We added hood and cheek louvers to let hot air out of our engine compartment, especially at lower speeds. The results are significant, and, while coupled with increased size in transmission cooler, also reduced our measured engine coolant, oil, and exhaust gas temperatures under similar conditions.

The hood louvers do allow some rain/snow and leaves to enter the engine compartment, though we placed them such that the water coming in does not drip on much affected by water. In fall I toss a tarp over the hood if we are parked under deciduous trees. When parked and idling after a hot drive the heat pumps out of the louvers, and seems to reduce the amount of heat that comes through the firewall/doghouse into our cabin.

I did place the hood louvers as far to the sides as possible given our hood construction, and have verified by yarn tufts while driving that air is exiting rather than entering at speed. Further toward the hood/windshield junction in the middle is usually considered a high-pressure area and might push air into the engine compartment, adding back-pressure to the radiators and reducing effectiveness.

Little write-up I did at our web-log soon after installing: www.badgertrek.com/sportsmobile/vehicle.shtml#Louvers



-e

[LaOutbackTrail]

Thanks for the info and pic. I can't tell though, are the louver openings facing forward or back?

[etbadger]

Thanks for the info and pic. I can't tell though, are the louver openings facing forward or back?

Our hood louvers angle to the rear to exclude water when we are driving in rain; this does allow rain in when parked, however the louvers are about 1/16" thick and rain that lands on the hood away from the louvers just runs around them. It is quite possible to put a plastic tray under the louvers to route incoming water away, but has not proved necessary where we live. The cheek vent louvers angle down.

-e

[FellowTraveler]

I did place the hood louvers as far to the sides as possible given our hood construction, and have verified by yarn tufts while driving that air is exiting rather than entering at speed. Further toward the hood/windshield junction in the middle is usually considered a high-pressure area and might push air into the engine compartment, adding back-pressure to the radiators and reducing effectiveness.

Little write-up I did at our web-log soon after installing: www.badgertrek.com/sportsmobile/vehicle.shtml#Louvers



-e

Great setup that vehicles body is perfect for how you did the venting, well though out!

[Box Rocket]

Couple of thoughts. Proper hood vents will release more heat than fender vents generally because of the reason you mentioned already. Most vehicles have too much crap bolted to the inside of the fenders to allow clean air flow out of the engine bay. Remember that heat rises so having the vents on the hood is putting them where the heat is trying to go anyway. Fender vents are typically used to release air pressure since wheel wells are high pressure areas. That's why many sports cars (racing vehicles) have vented fenders. I'm not talking about the style ones that are common these days and mainly aesthetic. On a sports car high pressure is built up in the wheel wells and reduces downforce. Not good when you need traction at high speed and the pressure increases with speed. So by venting the fenders the pressure is reduced and greater downforce is maintained.

I mention pressure because hood vents will not be effective if there is positive pressure outside the vent that won't let the air escape. Louvers work ok because the louvers have a series of raised fins with the opening behind the fin. As air travels over the fin that air must travel faster (similar to an airplane wing creating lift) and as the air passes over the top of the louver it creates negative pressure where the opening is and allows hot air to escape. So, if you were to simply cut a hole in your hood and put some mesh over it it wouldn't be as effective at releasing heat since there is positive pressure on top of the hood as air passes over it unless you were to create some kind of "lip" or raised area in front of the vent to create an area of negative pressure.

I'll use a Mitsubishi Evo as an example. This Evo has a fairly large vent. The large surface area helps by allowing an unrestricted area for air to escape, but in order to improve the effectiveness you can see how the engineers added a raised "lip" around the forward edge of the vent. This is what creates negative pressure as air passes over and its effectiveness actually increases as speed increases and essentially creates vacuum to actually suck the hot air out of the engine compartment. This is critical on the Evo because of the turbocharged motor that loses it's ability to create high levels of boost in "heat-soaked" conditions.



So to answer you question a combination of proper vents and a hood scoop could be an excellent way to reduce engine bay temps. The hood scoop as someone mentioned is best served by having it feed cooler air directly to a closed air box. Cooler air feeding the motor is going to drop running temps. But the scoop can also be used to force air into the engine bay to build an area of high pressure in the engine bay where air wants to escape. If there are vents for that air to escape then the scoop is going to help "push" the air out while a good vent that creates low pressure outside will "suck" air out. Best of both worlds.

Long winded techinical response, but hopefully it makes sense.

[HenryJ]

I had been looking for a way to vent underhood heat, much as the cowl hood did for my last truck. I did not like the engine heat vented right where the air is picked up for the interior though. No cowl hood for this one.
I did lots of looking for something that might work. There are several louvered panels available, but I'm not so happy with their appearance or methods to attach them.
I came across this install : Oman 4x4 Hood Vent Install
My search for new louvers ended when I found out they have been discontinued and the few that are still out there underwent a substantial price increase. $160 plus freight was more than I was willing to spend.
One local yard had two Pontiac Grand Prix the correct years. They had checked the green one last week and forgot to call me to tell me they were gone. I saw that they had a white 1996 hood with louvers. They had not checked out that one. I offered to come over and check it out.
Over the hill and through the snow! It was iced over and had six inches of snow on it, but they were both there. The hood was 80% , but I knew the guy running this yard and he was willing to let them go. I shoveled the hood off , pulled them and $20 later they were mine.
Returning home I coated them with paint stripper and removed three layers of white paint. I'd say this car had been repainted more than once. Down to original paint, I scuffed them good and gave them a coat of black satin Krylon Fusion.



There are a few minor imperfections, but they are not too bad.

I had already laid out templates and spacing earlier so once masked off things went pretty quickly.
Sixteen holes drilled.



I would have liked them farther back and more toward the outside, but hood braces hindered any other positions. This was the only place with space enough on the underside. These need to be functional, so there was no other option.
I cut out the big holes. Then I installed the hood insulation and chalked it to cut holes on the interior. Once that was ready I painted the raw edges of the hood , trimmed up some 1/2" neoprene to fill the void and hold some tension on the screws, attached the screws with fender washers and reinstalled the hood insulation.



The open area of both add up to 12.5 square inches (.25"x5"x5x2 ) The design of the louvers creates a low pressure zone behind each opening. At speed that should draw heat out. At low speeds at least it has some where to go. You can really see it boiling out heat at a stop sign.



They have been working great for me.

[LaOutbackTrail]

Thanks, good info there and good points.

I'm looking for a Subaru Impreza scoop now and have the intention of doing something along the lines of this:

I'm linking the idea of having the hood scoop in the first third of the hood and the venting lovers near the back third of the hood as illustrated by the 1's. Or, have the hood scoop set further back and use long skinny louvers on the sides.



But I'm really leaning towards this...

[LaOutbackTrail]

I like the styling of those Henry. I'll have a look the next time I'm out at the junk yard for mid 90s grand prix.

It looks as though 2002/2003 Subaru Impreza WRX have the right style (for me) hood scoops, and they bolt on.