Hood louvers and hood scoops

[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.

 

[FellowTraveler]

Fender vents difference as I see it.

Body style and type of vehicle aside Fender vents are used in various ways.

1) Fender vents at top and at trailing edge of fender and vented directly into engine bay/bonnet evacuate air always lip or not, however lip @ leading edge of opening is preferred method .

2) Fender vents at trailing edge of fender frt/rear of vehicle and vented directly from wheel well are for reducing pressure in wheel wells and help the cooling of brake components.

3) Fender vent at leading edge of fender and ducted to brakes cools brakes and complements wheel well vent if installed.

4) Fender vent at leading edge of fender ducted into intake or cabin.

Other uses are sure to come into play and not written in stone.

 

[corax]

As has already been said, vents will do better in the low pressure area near the front of the hood (i.e. between the radiator and front of engine). Here's a great 3 part article that I found a little while back, well worth the read before you start cutting your hood

AutoSpeed: Undertrays, Spoilers & Bonnet Vents, Part 1
AutoSpeed: Undertrays, Spoilers & Bonnet Vents, Part 2
AutoSpeed: Undertrays, Spoilers & Bonnet Vents, Part 3

FWIW, wish I would have read that article before I installed my Ford T-Bird vents - 6 inches forward would have made a world of difference as measured by my Magnehelic gauge

 

[brian90744]

heres mine on the ford ranger (black hood), yes louvers release engine heat.

I'm seriously considering installing hood louvers on my Montero. I'm also considering and pondering the effects of installing a hood scoop.

I understand the functionality of add louvers, they let heat out, at pretty much any vehicle speed. But my primary concern with a hood scoop is that it may disrupt the proper flow pattern for pulling air through the radiator at highway speeds. Sure, it will force (cooler) air into the engine bay, but I'm worried that the pressure would be to great, limiting the efficiency of the radiator and fan.
And for the record, I'm less concerned about looks than functionality.

Thoughts on this subject?

 

[LaOutbackTrail]

As has already been said, vents will do better in the low pressure area near the front of the hood (i.e. between the radiator and front of engine). Here's a great 3 part article that I found a little while back, well worth the read before you start cutting your hood

AutoSpeed: Undertrays, Spoilers & Bonnet Vents, Part 1
AutoSpeed: Undertrays, Spoilers & Bonnet Vents, Part 2
AutoSpeed: Undertrays, Spoilers & Bonnet Vents, Part 3

FWIW, wish I would have read that article before I installed my Ford T-Bird vents - 6 inches forward would have made a world of difference as measured by my Magnehelic gauge

Here's an excerpt from the first article:

Bonnet entrance vents – eg to an intercooler – are located and shaped to build-up a positive pressure on one side of the heat exchanger. For example, this Impreza WRX uses a very large forward-facing scoop to cause increased air pressure on the top surface of the intercooler. If at the same time there is a lower pressure on the other side of the ‘cooler, air flows through it. However, this in turn directs more airflow into the underbonnet space, creating an even greater need for a lot of exit flow capability.
So if you've added a bonnet scoop to pick up air – or you have enlarged the standard scoop – it's quite possible that there's a pressure build-up under the bonnet which is dropping the efficiency of your radiator, intercooler, oil cooler and/or air-conditioning condenser.
Get rid of that pressure build-up and all of the above will work better...

Then a few lines down suggests using a magnahelic gauge. I have about 10 of them at work that we don't use any more... I do forsee commandeering them for this project.

 

[FellowTraveler]

Lower engine bay cover

Manufacturers install engine bay covers under vehicle for a reason case in point my 1999 GMC Suburban had a large composite cover attached at lower part of front suspension/engine cross-member and extending up and forward to the radiator support what this did was prevent high pressure air from entering engine bay just after radiator shroud this prevented flow issues through radiator, what happened in my case was that I installed an aftercooler in area where the cover was then installed a spoiler to force air through aftercooler this stalled the airflow through the radiator, bad move.

Again, pay close attention to air flow into engine bay specially through hood vents because when vents are placed too far past radiator they become air intakes at speed period.........................if that air coming into your engine bay is too great it can and will stall flow through your radiator.

Autospeed articles read them!

 

[Ray_G]

Pretty happy with the vents from here: http://www.hoodlouvers.com/products.html#productshood

Don't have scientific #'s but do have a constant eye on the temp gauge (it's a Land Rover V8...comes with the territory) and have watched both the standard hood I kept and the vented one as it relates to the stock gauge. Will have a SGII hooked up soon and can keep a closer eye on it. Primarily done for low speed heat escape vice on road cooling (which is adequate in stock form).
r-
Ray

 

[grandpa]

LaOutbackTrail, any updates on the hood louvers on the Montero? I'm thinking about this also.

 

[LaOutbackTrail]

Its not the highest on the priority list, now that its coming Winter time and we're just now starting to use the truck. I thought about getting the Pajero hood scoop as there are reinforcements under the hood (even bolt holes) minus the hole in the hood. Problem with the Pajero scoop is that there's really no point to it, since its not positioned optimally for anything other than the intercooler on diesel engines.

Another issue I ran into is that the underside of the hood is asymmetrical. It will be difficult to place the louvers without cutting away at any of the supports.

It's on the list right after finishing the fabrication of my cargo barrier, drawers, ARB fridge slide out, fixing the heater, sliders, skids, camping table, etc etc etc.

 

[grandpa]

I understand about the "list". Mine is growing. I'm going to research this for maybe a summer project.

 

[XJINTX]

Scott you've probably seen mine but I like the cooling performance I get with mine. I also like the fact (warm fuzzy) they have the bottom deflectors to move water away from engine.