It sounds like the Kapton ship has sailed, but just in case it hasn't, I noticed that you had the aluminum side of your aluminized Kapton facing out. Would it make a difference if you switched it around with the copper side facing the heat?
Just a thought.

 

Actually, those vents are standard. Here's a pic of my slightly customized E Jag from 1969.

 

Thanks for the suggestion! Actually, the cool looking copper side is the coating on the back side of the mylar itself and is easily scratched by sharp objects. That was designed to be the backside, with the mylar facing outward.

The silver side is easily wiped clean and is pretty tough, even with repeated handling.

 

Love the E body types! Gorgeous, sexy cars they are. A coworker has a recently finished convertible and we all stood around and gawked happily at it.

 

Yes thought they were but my question is do they do a good job of evacuating the engine bay heat.

 

OK, here we go. To answer your question, Airborne Silva, we're going to find out within a week or so, because the hood grills are done and we're going to be deciding which configuration we want to go with. At least the heat in the Jag has somewhere to go! Versus, the sealed box that GM designed on the C3 Corvettes, where the heat has NOWHERE to go, but down and out the minuscule spaces on the bottom of the engine compartment by the frame!

First, the grills are raw metal, have not been polished yet or mounted. They are just laying on the hood to get an idea of how it would look. So expect the ends to be off the surface. Also, we are going to bevel the edges, countersink all the holes and use a router, so that the grills will be flush with the surface.

We are contemplating different finishes as well, including powdercoating in black, white and other colors, as well as polished aluminum and stainless steel.

 

Two configurations are possible. You can do it either way, but it's going to be tough deciding on which one, because they both look good.

Down the sides of the hood:



Close up:




The second possible configuration, right down the center:



Outside and looking at the center option in the sunlight:



Remember, these are just laid down on the surface of the hood, no polish, no fasteners. I just wanted to give an idea of what it's going to look like and based on what I see, I'm cutting the holes and then we're really going to find out if it works.

With that much grill area, it would be hard to believe, that heat won't escape up and out, even through natural convection (sitting still) and air flow across and into the hood while moving.

 

I'm at work and can't see the pictures right now, but really anxious to see the pictures and hear about the results. This is a great thread...one of my all time favorites!

John

 

Hey F22,

To me it would make more sense to have them towards the outside of the hood - above the exhaust area. Also, it might be easier to work with given the flatter shape of the hood in that area.

Now that I'm seeing these laid in place, I wonder what they would look like painted body color? Might look pretty good that way!

For testing purposes, can you find a used hood to experiment with? Should be reasonably priced I would think.

Adam

 

Hi Adam, I have to agree about the placement. I think too, that being right above the exhaust as you stated and also, on the outside of the engine block on both sides would be more of an advantage than the 'centered' on the cowl hood look ('though we were stoked at how it looked).

As far as a used hood, that is a used hood! The car has a lot of, let's say 'patina' that I have polished out, stretch marks, wrinkles, fading and all. But it is the original paint, from the original paint, that got redone, when the whole front clip got replaced at some point in 'Sassy's life!

Painting it the body color would be very cool, but might be tough to match up for some, thus the experimental, bare metal look for now (but it will be polished up) and also, I can widen the holes and narrow down the structural aspect of it, but I wanted to go with a little 'beefy' to start, to see how it holds up under real world conditions.

It's going to be interesting to see how it works.

PS: John aka Ludemjo, let me know what you think of them, I think Adam's idea of body color paint is pretty cool and it may make it more integrated at least with the 74-77 Corvettes. If this works, I've got some very, very cool patterns and finishes that I want to experiment with for the '78 - '82 Corvettes as well.

 

This is a very crude job (sorry... not much time today) but gives an idea of what they might look like painted. Squint your eyes a little and that helps

 

Sigh, our workplace 'filter' won't open it! I'll just have to imagine it, but for now, the focus is going to be on the results. For that, I'll have to take it out for at least an hour, because that's a reasonable estimate for how long it takes for the heat to soak everything and start to come through the firewall and eventually, you in the passenger compartment.

 

No worries... I know it's sort of the cart in front of the horse. Just and idea Take a look when you get home tonight.

Agreed on the time thing. Depending on the air temp here, it's about a 30 minute drive or so before it really starts to heat up in our '77.

 

Where does the heat go? I found a linkee from an Engineer, that explains exactly what happens to our Corvettes. This is for diesel trucks, but boy, the story is real familiar....

http://www.rdac.com/resources/blog/w...t-go-check-cab

Where Does Underhood Heat Go? Check the Cab

As engineers, one of our biggest challenges is how to deal with underhood heat. Because of aerodynamics and other styling changes, the engine box on trucks is smaller and more densely packed than it ever has been. Add a hotter-running diesel engine (the result of emission controls) and a smaller grille area, and the thermal environment can get downright nasty.

It’s particularly true of 2007-model and later on-highway diesels, which heavy-duty parts and service shops will see more of as these trucks come off warranty.

While heat under the hood is an issue for the durability of hoses and other components, we’re especially concerned about the effect on the cab and the operator inside. Unless the truck manufacturer makes physical adjustments to the cab in terms of thermal insulation, heat from the engine box can be absorbed into the floor, doghouse, and other surfaces inside the vehicle. We’ve measured surface temps on metal seat bases, floorboards, and engine tunnels running 140 degrees F.

This is an additional load for the A/C system that didn’t exist before. The situation is similar with cleaner-burning diesels in off-highway equipment, which have even more steel plus the additional heat load of the hydraulics.

When you’re dealing with engines built to meet tougher emissions standards, it’s doubly important to check the A/C system thoroughly and to replace worn-out hoses and other components with OE-quality parts.

If you’re getting complaints about the A/C not working well, or you’re spec’ing an aftermarket unit, remember that a hotter-running diesel can increase the heat load in the cab. Take that extra heat into account.

 

Another great article and it even shows the 'Sealed Box' of the engine and the overall effect on airflow! If I'm reading it right and if the Hood Grill mod works, it will also help the radiator flow more air through it as well. Written by a Brit, so substitute "Hood" for "Bonnet".

http://www.autospeed.com/cms/A_2159/article.html

 

Wow, the more I read, the more I understand the Thermal Management part of working through this. This is for a truck, but I can't imagine a car being much different. We're looking at underbody air flow.

Note the laminar air flow UNDER the vehicle, with little effect on the engine compartment.

http://nestor.coventry.ac.uk/~bastie...Simulation.pdf



Here's the wrapup in the same article. "The main reason for such thermal inertia (heat soak, as we call it) is improper air circulation".




If that's the case, what if you had spring loaded air scoops beneath the body around the bottom of the engine area that would be slightly canted and open with increasing wind pressure, closing when coming to a stop, versus the 2" inch ram air tubes from behind the turn signal grills?

_______|

\
/
/
/

 

I just finished digesting all your reference materials and I definitely feel you are on the right track. I agree completely that the vents should be placed on the outer edges. This position, puts them basically over the exhaust and any water that may get in when you are parked or standing still will fall in the space between the engine and the wiring/electronics mounted on the fender well. On the move, water should not be an issue at all as the air flow from the vents should, it is hoped, keep the rain out.

The vents look the best painted to match the body color. I still think the vent area may be excessive, but testing will prove that out one way or another. Airflow testing with yarn tufts will also be important to ensure the flow direction is as we expect and there are no reverse flow tendencies.

I am having a little trouble warming up to the design though. I like the Jag vents, and would think something like that, mounted flush may look better. Given that my car is black, I have visions of carbon fiber as well, but that's just me dreaming. I am a little concerned that the vents on the forward half of the hood will reverse flow and then outflow in the back half and not draw as much heat from the engine compartment as we are expecting. The vents on the Jag are perpendicular to the airflow and would draw the heat out. It would be very difficult to have reverse flow into those vents the way they are designed. I will IM you tomorrow with some vents I have been looking at.

Sorry for being so late to respond...been kind of crazy with the government shutdown and my job.

John

 

Definitely one of the most interesting threads going. I too have been following all of the comments and I'm very interested. I like the concept of the vents running down the side of the hood but personally, I would like to shape them to match those on the top center. Keep it going, good stuff!

 

Great feedback, thougths and ideas too. The louver style definitely has nice design and functional aspects going for it, that's for sure and I agree too, that a body color would be less of a visual take-away from the overall appearance of the hood.

So I'm going to paint the grills, with a spray can, that I had mixed, custom for this car. I dropped off a T-top, so they could match it and they got it, very close for $25, and I almost forgot I had it. So thanks for the inspiration, I'm going to apply that.

Insofar as design itself, I will do the yarn tuft thing after the install and see what happens. Here is my bastardized, ahem, 'theory'. I'm thinking with the long length, laterally down the hood, I envision a 'scooping' action between the input of the low pressure and the output of high pressure, or it could be as simple as 71" x 4" of air vents, getting the heat out.

 

The thing about air, it's horribly non-linear. You can't really assume anything about a vette based on a truck simulation. I'm sure the side vents on the vette and the lower ground clearance do change the flow a lot. Also, from that diagram, it's really hard to say just how much the airflow under the car is affecting the air flow around the engine, not enough information to say that it's having "little effect", the air flow under the car SHOULD be much larger than the flow around the engine on a truck... if it's not, something is probably horribly wrong. That vector plot is also very hard to actually read, there's no scale on it and it's only a 2D vertical slice, I think a horizontal slice or a front on slice would be far more telling. Having done CFD and wind tunnel testing before, I can tell you that you end up chasing your tail, you try and capture a high pressure region and it moves somewhere else, try to disrupt a vortex and it just gets diverted instead, try and change the flow direction and it just moves somewhere else but in the same direction. Can be a real headache, but it's fun to play! But I think you're on the right track with your hood venting anyway. Personally, If I were modifying my hood and car anyway, I'd go for massive venting. I'd go for several large crossways slots in the rear corners of the hood, use an L88 style hood (as that has a big opening at the rear behind the air cleaner), and I'd even be tempted to do some C6R style venting in the top of the fender area.

I have an L88 style hood on my 1971, a lot of heat comes out of the opening just in front of the windscreen. You can see the heat haze rising from the opening even on days where you typically wouldn't see heat haze.

If I wanted to race a C3, I would grab an L88 style hood, get a new radiator that's not at the stupid angle GM put it (obviously will take some modifications), put a splitter down low which has openings in the top to feed air to the radiator (otherwise the high pressure on the splitter will act on the lower curved section of the nose, increasing front end lift), modify the front middle section of the hood to have a big opening just behind the radiator (similar to a C6R, but just venting the engine bay as a whole rather than just purely the radiator), then vents on the rear corners of the hood and also might throw some extra venting where the opening is.

I'd then try and close off as much of the bottom of the engine bay, and hope that the hood venting was sufficient to cool the car.

That's obviously just a 1st iteration guess, but IMO I think it would cool well and get rid of the nasty front end aero lift.

The best way to test aero stuff is to have a pile of disposable parts (hoods, fenders, etc) and just start hacking them up, use plastic or even cardboard (as long as it isn't in an area that gets too hot) to play around with different configurations and such. Get some sensors in there and see what works best. Even measure the front end aero lift, as I think one benefit of good hood venting would be to reduce that.

Frankly, the C3 engine compartment is so damned tight and restrictive, pretty much anything would be an improvement, but the engineer in me always wants to test and optimise things

Personally I think the C6R is vette aero done right, so if all else fails, try and make the car less C3 like and more C6R like

EDIT: Keep thinking of different things to add, lol.