Hood Scoop, air flow, and hood Louvers

[Jazzman]

Heat dissipation is always a concern here in Arizona. I don't expect to be driving the car when it is 115 degrees. I want to do whatever is necessary to keep the engine running at reasonable temperatures, both for the health of the engine as well as my own comfort in the cockpit. I know that the Coyote engine is a tight fit in the engine bay. I am considering adding the hood louvers to allow air to flow in the front and bottom and easily up and out through the hood. I just don't think the little side louvers will provide enough air flow to adequately vent the hot air. (Of course, these were originally race cars designed for very hard use. Who am I to second guess the original designers?! Oh well, I will second guess anyway!) Since the Coyote engine has no air intake anywhere near the hood scoop, is there any reason to make the scoop functional? Would the incoming air pressure from a functional scoop cause disruption of the upward air flow toward the hood louvers? Would this be a good or bad thing? Is any air flow good air flow? My tentative plan is to make the scoop non-functional, but I would appreciate the advice of those who have greater experience, especially with aerodynamics.

[skullandbones]

Hi Kevin,

Personally, I love the hood louvers and there is support for your thoughts if you look at the race car pics (don't think they added them for looks). I won't even start an argument for or against based on aero. I like them because heat rises and you will dissipate heat at rest and low speed. Your radiator with an efficient fan/shroud system should take care of the cooling at rest and low speed. I'm running a small push rod engine. But the Coyote has to have modern tech on it's side as far as the latest cooling tricks (casting, etc). I, too, am based in AZ. I have not had any overheating problems here but I do avoid the 115 degree heat during the summer days. You still have early in the morning and some evenings to exercise your roadster during the summer. I'd leave the hood opening functional as well (deleting the hood with louvers is another way). Another thing is the advantage of ceramic headers. It will reduce the engine bay temps. I've done direct measurements on mine. There is a definite differential between the headers and collectors just south of the headers. The untreated steel gets hotter and retains the heat more than the ceramic BBKs which are treated inside and out.

My vote is to go with the hood louvers.

Good luck,

WEK.

[2bking]

I had the same issue with the hood scoop as far as air intake and the aero effects. I've read quite a bit about the pros and cons but like the look of the scoop. I decided to mount the scoop but not cut the hole in the hood. What some have found with the hood louver testing is they allow air to pass both directions. At higher speeds the high pressure in front of the windshield pushes air back into the hood.

[BEAR-AvHistory]

NC is not AZ but it does get warm. Hood is normal with an open scoop & no louvers. Never had the engine hit the 200*F mark on the temp gauge even sitting in summer traffic. Car does not yet have a radiator shroud installed.

Will be installing a shroud over the winter for another reason but for AZ it should be a good thing to do.

[Jazzman]

At higher speeds the high pressure in front of the windshield pushes air back into the hood.

Wow, I never even considered that possibility. Interesting. Thanks!

[CraigS]

I like the louvers and I think they help. At speed a normal radiator w/ a good fan and shroud works fine. Stopped or creeping in traffic is where the problem is. In that situation I feel the louvers will help. I know that in the summer, between autocross runs, if I open the hood, that has an obvious effect on the engine temp. King is correct about the high pressure at the base of the windshield, but I don't know how far in front of the windshield that extends. I suspect that it does not extend to the usual louver positions I have seen where the rearmost opening is 5-6 inches forward of the hood opening which puts it about a foot in front of the windshield.

[edwardb]

I can't cite any aerodynamics or anything else scientific for that matter. But that doesn't keep me from having an opinion. :rolleyes: Even though I've never done them, I like the look of the hood louvers. Done well, they're a very cool add to the overall appearance. But conceptually I don't quite get having a non-functional hood scoop and then adding hood louvers. Wouldn't be my personal choice, but that's just me. I agree the Coyote doesn't have the cold air intake in the general area of the hood scoop. But the intake runners are all directly in the that area, and cooling air would be a good thing IMO. My Coyote build will have a functional hood scoop. At this point, I don't have any plans to add hood louvers. But Michigan is just slightly cooler than Arizona. One thing not mentioned in this discussion is how open the engine compartment is. Much more than most modern DD's. There is no aero on the bottom side. The F-panels and splash guards are from sealing airflow. The side louvers are another open path for airflow. Lots going on there. I agree with the comments that the main overheat concerns are going to be a low speed and stop and go. At speed, there will be lots of airflow from multiple sources.

Other more general comments regarding cooling. Look at it as a complete system, not just airflow. With a complete kit you'll get the AFCO aluminum radiator. That's a quality piece with lots of cooling capacity. Add a fan shroud and it will be even better. I would also recommend taking a look at how the cooling system is hooked up to the engine. FF hooks up the Coyote like all the other engines, with a T-filler in the top hose and a standard overflow tank. The Ford setup is with an expansion tank and several connections between the engine, tank, and radiator. That's what I'm doing in my build. I'm going to trust the engineers at Ford who design this thing to run in extreme climates all over the world. Also, are you running a heater? If so, OK. But if not, Ford recommends a bypass hose between the heater inlet and outlets at the front of the engine. The standard FF Coyote instructions say just to cap these, although I've heard if you call tech support they agree a bypass is recommended. This apparently also helps with cooling. And if you want to go one step further, there are certain coolants (e.g. waterless) that claim to lower operating temps.

[2bking]

I don't think hood scoop or louvers has much impact on cooling unless some air management happens inside the engine compartment. There is no evidence that the engine relies on cooling from surrounding air such as heat fins and much of the engine surface is covered by plastic indicating the cooling is done internally through the coolant. The headers are responsible for most of the heating under the hood so good thermal management (reflectors, insulation, header wraps, ceramic coatings) can mitigate the effect. The worst thermal problem happens when the car isn't moving and no wind thus no air flow except through the radiator forced by the fan. Once moving there is copious amounts of air flow everywhere to cool the under hood temperatures. Air flow has no effect on the radiation of heat from the headers except to cool the surfaces that receive the radiation. Polished reflective surfaces have the least radiation, maybe 1 to 5%, and is an excellent way to prevent the radiation at the source (think chrome headers, polished stainless headers). A flat black surface has the most radiation so painting the headers black will produce the highest under hood temperatures.

I've read through quite a few threads regarding the changes made to help these cars achieve better stability at higher speeds. The aero effect the scoop produces adds pressure below the hood making the front end lighter at higher speeds (80+ mph). The ones racing in certain classes are required to have the scoop but they block the opening. The scoop and hood louvers fight each other with the scoop forcing air below the hood and the louvers trying to let it out.

If you are not planning to compete on track, the scoop or louvers won't make any difference on the streets so do what you want. I like the hood louvers but they just wouldn't work for me because of the ribs I had to put under the hood for my tilt front.

[Jeff Kleiner]

Although it is beyond the actual scope of this conversation I think it's interesting to point out that there is a bunch of air pressure under the hood at big (triple digit) speeds. Competing at RunN'Gun a few years ago I was on the main straight at Gateway when Tony Martin launched his Backdraft hood about 100 feet in the air at about 150 MPH! I stopped by the trailer later and found them taking 6" hole saws to the hoods of other cars and turning the scoops around backwards to let air escape!

I know that the louvers allow some heat to escape when the car is stopped after having held my hand over them on a car I built. Whether that continues to occur when moving at traffic speeds I can't say. I will tell you that there is a fair amount of labor involved in prepping and finishing the hood for them. To compound matters this particular car is a Mk3 which had the molded in scoop---the owner wanted a bolt on scoop so I first had to cut the molded one off, fill the hole then cut it out for the loose scoop. About the time I got that done was when he decided he wanted the louvers too...more holes and bodywork! There's probably almost as much time in that hood as in prepping the rest of the body, but it sure does look cool :)

http://i269.photobucket.com/albums/jj43/jkleiner/Aaron5171/100_5443.jpg

http://i269.photobucket.com/albums/jj43/jkleiner/Aaron5171/100_5463.jpg

http://i269.photobucket.com/albums/jj43/jkleiner/Aaron5171/100_5449.jpg

It would be interesting to see how they look without a scoop.

Cheers,
Jeff

[bansheekev]

Here is another example of hood louvers on a MKIV Coyote build. Looks like the same ones as Jeff shows except mine are painted the car's base color...

475654756647567

I had a very similar thought process that you describe. I think the most significant benefit is letting hot air out when in traffic or stopped to avoid head soak.

Kevin

[walt mckenna]

I have an old Motor Trend Retrospect illustration of an original 427SC Cobra. It shows the air cleaner, on the carburetor, up in the space made possible by the hood scoop. Cold air and clearance are probably the only good reasons for having a hood scoop with the exception of personal preference. I chose a smooth hood because I like the clean lines and my engine does not interfere with the hood.

Auto manufacturers are not too concerned about under hood heat, so I was not concerned about it except for how it affected cockpit temperatures. With that in mind, I insulated both sides of the firewall and footboxes and left the gap between the top of the radiator and bottom of the hood open so that excess air coming in from the front of the car would keep under hood temperatures near ambient. I have no problems with engine heat affecting cockpit temperatures.

As far as aerodynamics, these things do not do well in that department. Unless we want to close off most of the openings, install an air dam to keep air from going under the car, and install a top to direct air over the top of the car, we just need to live with what gets us all those thumbs-up.

The Coyote is an all aluminum engine like mine and I have no coolant or oil temperature problems. The FFR radiator along with a Breeze shroud takes care of the water in any ambient or track conditions and a good pan, like a Champ Road Race pan with full windage tray, does a good job of helping with oil temperature (my oil typically runs 140 in cruise mode and 180 at the end of a 20 minute track session in summer.

Scoops and Louvers are items that can help personalize your vehicle, but probably not necessary. Those Louvers do look good though, don't they?

[chopthebass]

Jeff, those louvers look great. Are they a one-off or can they be bought?

[Jazzman]

x2 to Chop's question: Jeff, Where did you find those louvers? They look very well built. Beautiful car, by the way!

[Boydster]

I'm still in the planning stages, but these are on my must-have list:

http://vraptorspeedworks.com/mk4-roadster-hood-louvers/

[CHOTIS BILL]

When it comes to air flow I am reminded of a quote from Bill Campbell the owner of Campbell Boats back in the 50’s and 60’s. He took a 500cc lakester, dropped in a SBC, and then added a less than aerodynamic body. He took it to Riverside Raceway that had a straight over a mile long and took the top speed record away from Ferrari at over 180MPH. When it came to aerodynamics he said “ I don’t know which way the air is moving but I want it moving”. So he had many openings to keep the air moving. That is kind of how I think of adding lovers

Bill Lomenick

[bansheekev]

I'm still in the planning stages, but these are on my must-have list:

http://vraptorspeedworks.com/mk4-roadster-hood-louvers/

Those are the ones in my car. Actually some of the pictures in that link are of my car :cool:

Kevin

[skullandbones]

Those examples of louvers are nice. I remember seeing some on a roadster racing (a sixties era pic). The configuration looked more old school louver style. I saw a similar one on a 4x4 website. They were 15.5 x 4 inches but that fits pretty nicely on the roadster hood. They are black aluminum and about half way down the page (set of two). I think the body work would be less challenging on these but you would have to finish the inside so that might be about the same. Here's the link.

http://www.4wheelparts.com/eSearch.aspx?Ntk=primary&Ntt=hood+louvers

Regarding the scoop positive pressure under the hood: I'm going to fabricate a reverse turkey pan that attaches to the hood and will fit over the 8 stack through a plate with 8 holes (careful fitting). The filter will rest on the stack openings. I believe the isolation of the scoop air will be enough to reduce the bad effect of the pressure in the engine bay at high speed. It should also limit the hot engine bay air for the induction system. The good effects of the louvers should still be felt. I just don't like the idea of having two applications cancelling out the advantages of each other. If the Coyote induction system can be hooked into something like this, you could "have your cake and eat it too!" Just a thought.

WEK.

[Jeff Kleiner]

x2 to Chop's question: Jeff, Where did you find those louvers? They look very well built. Beautiful car, by the way!

From Shane at Vraptor:

http://vraptorspeedworks.com/custom-roadster-parts/

Jeff

[russelljones48]

Don't want to take this too far astray but underhood intake temps can impact performance - not sure if there's a dyno analysis done yet on the other site but isolating the Coyote intake and using ambient air appears to have improved HP

[CraigS]

Jeff K, On the shots of Shane's louvers I see rivets on the underside but not the outside of the hood. Is that hood a double layer of glass so you rivet only to the underside layer. Trying to figure how I could do them on my MkII hood which is single layer maybe 1/4 inch thick in most areas.

[chopthebass]

Good question Craig. I wondered the same thing. I know when cutting the hole for the hood scoop in a mk4 there are two skins to bond back together, so I am guessing your assumption is right. Not sure about MKII though.

[Brett33]

Has anyone put Shane's louvers on a 33? Either hood or side panels?

Brett

[Jeff Kleiner]

Jeff K, On the shots of Shane's louvers I see rivets on the underside but not the outside of the hood. Is that hood a double layer of glass so you rivet only to the underside layer. Trying to figure how I could do them on my MkII hood which is single layer maybe 1/4 inch thick in most areas.

Craig,
The car I showed in the photo above is a Mk3 so it's a double layer hood.

For anyone who is interested here's how I did it---I'm sure there are other methods. Like when you cut the scoop opening on a Mk4 the two layers have approximately a 3/16" gap between them. I cut paint stir sticks and slipped them between the layers around the perimeter along with some HSRF to bond them in place. I kept them about 1/4" back from the opening and then filled the remaining void with HSRF. After that set I used Rage Gold to smooth the opening and rolled the edges. Rather than riveting the louvers I actaully installed them from the underside with 1/4" long stainless sheet metal screws (#6 or 8 maybe?). These thread into the underside 'glass and into the wood laminated between the layers. As I recall I also added a few dabs of silicone between the louvers and hood. They aren't going to come loose!

Cheers,
Jeff

[skullandbones]

Craig,
The car I showed in the photo above is a Mk3 so it's a double layer hood.

For anyone who is interested here's how I did it---I'm sure there are other methods. Like when you cut the scoop opening on a Mk4 the two layers have approximately a 3/16" gap between them. I cut paint stir sticks and slipped them between the layers around the perimeter along with some HSRF to bond them in place. I kept them about 1/4" back from the opening and then filled the remaining void with HSRF. After that set I used Rage Gold to smooth the opening and rolled the edges. Rather than riveting the louvers I actaully installed them from the underside with 1/4" long stainless sheet metal screws (#6 or 8 maybe?). These thread into the underside 'glass and into the wood laminated between the layers. As I recall I also added a few dabs of silicone between the louvers and hood. They aren't going to come loose!

Cheers,
Jeff

Sometimes you just get lucky. I'm glad I have the MKIII hood now. I was wondering how I would do it specifically. So thanks, Jeff.

WEK.

[bansheekev]

FYI, Da Bat Jeff Miller did my VRaptor louvers and did exactly the same thing as Jeff. Cut openings, bonded in spacers to keep a gap, finish body worked the openings, and installed small stainless screws through the louvers into the bottom of the hood.

You can see the screws here:

http://vraptorspeedworks.com/wp-content/uploads/2013/12/image3.jpg

Kevin


Craig,
The car I showed in the photo above is a Mk3 so it's a double layer hood.

For anyone who is interested here's how I did it---I'm sure there are other methods. Like when you cut the scoop opening on a Mk4 the two layers have approximately a 3/16" gap between them. I cut paint stir sticks and slipped them between the layers around the perimeter along with some HSRF to bond them in place. I kept them about 1/4" back from the opening and then filled the remaining void with HSRF. After that set I used Rage Gold to smooth the opening and rolled the edges. Rather than riveting the louvers I actaully installed them from the underside with 1/4" long stainless sheet metal screws (#6 or 8 maybe?). These thread into the underside 'glass and into the wood laminated between the layers. As I recall I also added a few dabs of silicone between the louvers and hood. They aren't going to come loose!

Cheers,
Jeff

[CraigS]

Thanks Jeff

[BEAR-AvHistory]

Don't want to take this too far astray but underhood intake temps can impact performance - not sure if there's a dyno analysis done yet on the other site but isolating the Coyote intake and using ambient air appears to have improved HP

+1 Took ambient air from the oil cooler intake. Butt dyno says there is an improvement in performance. Might be a placebo effect but intuitively it seemed to be a good thing to do.

[gtaroger]

I have a MKII that I installed louvers in my hood. I used the 68 Shelby replacement louvers. They are made of fiberglass. I Cut the holes in the hood and glassed the louvers in from the under side. When the car is setting still with the motor running you can feel the heat coming out of the louvers.Roger

[gtaroger]

I have a MKII that I installed louvers in my hood. I used the 68 Shelby replacement louvers. They are made of fiberglass. I Cut the holes in the hood and glassed the louvers in from the under side. When the car is setting still with the motor running you can feel the heat coming out of the louvers.Have photos in my album. Roger

[Jazzman]

I ordered a pair of the Vraptor hood louvers last week, got them Friday. Quick service! Good job! They are a bit rougher than I expected. Appearantly they are cut with a CNC Plasma machine rather than a CNC Laser machine or CNC Water jet machine. I am debating having them powder coated, having them painted the same color as the body, or having them chromed. In every case, I am not making the decision yet, but I think they are going to take a lot of hand sanding and polishing to make them look nice and smooth. I am only evaluating them at the moment for what size and shape of hole I should cut in the hood. They did not come with instructions, which is a bit unfortunate. Oh well, I am sure I can figure something out. It looks like I will draw around the outside of the flat louver, then draw new lines 0.625" inside the original lines on the sides, 0.750" on the narrower front and rear lines. For those of you that have installed them, does this sound right?

[Jeff Kleiner]

...I think they are going to take a lot of hand sanding and polishing to make them look nice and smooth. I am only evaluating them at the moment for what size and shape of hole I should cut in the hood. They did not come with instructions, which is a bit unfortunate. Oh well, I am sure I can figure something out. It looks like I will draw around the outside of the flat louver, then draw new lines 0.625" inside the original lines on the sides, 0.750" on the narrower front and rear lines. For those of you that have installed them, does this sound right?

Correct on both counts. They take a lot of prep work depending on what finish you want to end up with, especially if you are going for shiny polished like the one I showed. Not so much for paint. If you decide to go body color I think I'd smooth them and then have them powder coated to serve as a well adhered base to work from with your paint. You're pretty much on track with your thoughts on measuring for the cutouts. As you finalize the openings don't forget to allow for the buildup of primer/sealer, paint and clearcoat (x2; both sides of the hole). If you paint the louvers factor it in for their edges as well. Good luck; there is a fair bit of work involved in them but they do look great when finished!

Jeff

[mikeinatlanta]

Shane make some nice louvers, and can custom cut them for any thickness of hood. I do wish he would switch over to laser or water cutting though.

RE the aero: I would suggest not taking any cues from the original race cars as they truly had no clue. Even the larger radiator opening for the 427 was a step in the wrong direction. Guys are on the right track looking at letting more air out rather than moving more air in. That said, louvers right in front of the windshield may give the best look, but won't give the best airflow. I guess you have to decide if you are looking for pressure relief at speed or letting the heat rise during stop and go traffic.

[j.miller]

If you decide to paint them...powder coat them first in a color close to your paint color. Paint loves to stick to powder coat and powder sticks well to aluminum. + the powder glues the center brace in place...da Bat

[Duke]

You should be just fine with side vents and a fan shroud. Your main issue is air flow to transfer heat. You'll have a large amount of air being pulled into the nose through the radiator, the engine bay will mostly be hot and a higher pressure, with the air being moved around the motor and out under the car and through the side vents. Most of the heat and air pressure from the engine bay is going to excape under the car as you don't have a belly pan under the motor and the air traveling under the car is a moving faster (lower pressure) so it will draw the heat and air out along with the higher pressure under the hood (from the radiator fan). If you have a hood scoop most of the air traveling through it will be coming OUT of the engine bay rather than into it. At highway speeds it will typically be equalized in pressure with no air in or out. The only time a hood scoop is functional is if you have it sealed to the intake and the motor is drawing air into it.

If you like the looks of louvers in the hood then go for it, but you don't need it. The fan, fan shroud, and radiator is plenty for the coyote motor, even at high ambient temperatures. If you are really concerned you can either have someone like ron davis or afco help run the cooling calculations numbers with you and make sure you have enough surface area and air movement for the heat generated. Any changes you do to improve cooling will be done at the radiator (larger or more cores) and CFM flow in the fan(s). Air removal from the engine bay isn't a problem as you aren't running a belly pan/sealing the motor bay.

Here's a good read on Aerodynamics for race cars to learn a little more. http://www.lateral-g.net/forums/showthread.php4?t=48400&highlight=air+flow