CKit

That's the thing that I'm disputing. I am saying that the engine bay IS ducted. Air goes in through the nose and radiator. Passes into the engine bay. If you seal the underside of the car, then you create a higher pressure zone in the engine bay that wants to go somewhere. Would you louver an exhaust? Nope. You're looking for the most open hole with the most surface area and the least edges to reduce resistance. Square edges add more turbulence to flow.

In my mind, I think: What if the big cut holes + louvered leading lip using rubber or plastic edging would extract more heat and flow. Then i wouldn't have to spend as much time cutting and it would actually be partially reversible (you could pin / latch the big cut out plates back in place on rain days or for storage.


Air and HEAT. It's ridiculous because if you're trying to remove air and heat, adding a square pit of cut out insulation has the same problem as the fluid dynamics of a flat hole from underneath. Imagine just the underside surface of a hood with air flowing. The deeper the crater (of insulation), the farther air has to travel to get to the low pressure zone (vent itself) and less effective that vent will be with the air just choosing to go somewhere else (like down underneath the engine and out).

I'm not sure if you understand that. Take a one inch thick board and stand it up on its side so it stands up. Now take a hose and spray in the same plane as the face of the board so water cascades over the face. Now cut a hole in the board and see how much water trickles through. Some, but not much as it'll want to pass over the face but some will escape (note the board has to be standing so gravity isn't forcing water through the face).

Now take a 6 inch thick board. You've just added thickness and distance for the fluid to travel if it wants to get to the other face. How much water gets out now? Less.

That's what the guy was doing by adding thickness to the vent channel by making a pit for the vent in insulation. It would have been smarter to cut a shallower, longer leading wedge out of the insulation and duct the tail edge of the insulation to help channel and draw out the airflow. But by having a "pit" with the leading edge being a barrier to smooth flow and adding resistance would decrease the flow.


You can't have it both ways. It is a street car or a race car? Do you care about quieting engine noise with a hood mat when the car probably has an CAI, test pipe and single exhaust? How effective do you think a fire mat WITH HOLES IN IT is going to be?

That's like keeping an umbrella with holes in it.

I have doubt in the results and would just buy an aftermarket vented hood. That cut up hood looks pretty amateurish and dangerous to the fingers. And hard to clean. And people have documented lower engine BAY temps with the big vents (so we know that does work).

If my time is worth $xx per hour and it'd take me xx hours to make the hood, it's not really free to me.

What someone CAN do, though... there are plenty of guys with the DIY vented hoods.
I'd love to see someone do the following:

1. Put tufts in the CENTER of the big holes. Not just the leading edge, but in the CENTER of the big holes. Mount it to something in the engine bay and see if the tufts peek out.

2. Do the experiment again with an adhesive rubber trim strip or garage threshold strip to make a leading edge on the big hole and see if that helps suck air out and bring tufts up more vigorously. Note that it wouldn't be about how high the tufts stand up, but how many get pulled through the hole (indication of "suction" or relative pressure differences across the two surfaces).

ScandinavianFlick

Depending on pitch and chord, louvers can act either as flow conditioners (increasing efficiency by reducing separation) or coanda effectors (directing airflow due to the propensity of a fluid flow to follow a surface it's passing over). The single-leading-flap method CKit is describing is also effective, but serves a different purpose- it creates a low pressure area at the forward edge of the slot to force extraction.

It must also be said that insulating the hood surface may actually be desireable, as the thermal expansion of the air as it passes through the radiator actually increases flow velocity (remember, PV=nRT). Heat transfer to the metal of the hood removes energy from the flow. Whether increased flow velocity is more beneficial than reducing the surface temperature of radiating bodies within line of sight of the radiator would have to be determined experimentally.

The most effective cooling mod for most street cars is a fully divergent-ducted radiator. That requires a lot of work, and increases the load on the fans when stationary. Whether the duct exit is a simple hole or louvered (you'll see both methods used on purpose-built race cars) is determined by whether cooling efficiency or repurposing the outflow (for example, feeding the underside of a wing) is prioritized.

Hope that helps.

CKit

Agree with this. It's the principle of wrapping turbos and pipes to increase velocities.

I agree that more shielding would potentially increase velocity of jet through vent and help aero more.

Was going on the primary assumption that the vents primary purpose was for engine cooling rather than aero and flow. For that reason, I was thinking that anything that helps trap heat in the engine bay would be counter to that primary goal.

Because if there's more velocity through the same size hole that means the heat and pressure gradient is higher, meaning that the engine is sitting in a hotter environment.

ScandinavianFlick

Ah, ok, I see where you're coming from, and from that perspective I absolutely agree. In the prior example I was considering it from the perspective of lowering internal engine temperatures by increasing the effectiveness of the radiator through improved flow.

GrandMasterKhan

I was thinking of this type of mod as well. I wanted to try the DIY hood vents but use the existing metal to create a lip in front to help draw out the air.

Honestly I haven't had the time to actually do it. but maybe you guys can enjoy my concept art.

CKit

Kind of cool art! I'd still do it with plastic stick on or drill on to prevent from cutting your hands.

spdracerut

That was the purpose of this hood. Per the first paragraph of the article:
"The destroyer of all track vehicles is excessive heat. Whether it is the coolant, various oils, or brakes, too much heat will lead to failures. On Project S2000, we’ve already addressed the engine coolant and oil temperatures with an upgraded Koyo radiator and Earls Temp-A-Cure oil cooler. These heat exchangers depend on airflow to in order to remove heat from the coolant and oil. No airflow means no cooling, hence the need for fans when the car is sitting still. One way to improve the airflow through the heat exchangers is to minimize the resistance to the air exiting from behind the heat exchangers. For the vast majority of street cars, all the air has to dump out the bottom of the engine bay. So how do we minimize the resistance to airflow? By increasing the area the air has available to exit. In this case, we’re venting the hood."

spdracerut

I'm confused on what you're talking about. So.....


This was my first hack at the insulation, but I felt it was a block to the flow path for the air to escape through the vents.


So I hacked some more with this being the end result. I was able to retain the plastic push-tab things at the corners and middle-front to hold the insulation in place.

The insulation was cut out of the way to give the airflow a straight shot out of the vents. That's what you are talking about right?

CKit

I just saw the pictures of the first attempt. Does anyone think that the second attempt serves any function?

That's bizarro.

The whole thing still seems grade school to me. A mish-mash of kinda sorta stuff.

So you're saying that the primary goal is to increase flow through the radiator?

If we discount aero and just take air flow through radiator as a primary goal, then there are much better ways of doing it than this hood.

Cooling plate for radiator.
Foam insulate and tape around sides of radiator and add nose splitter so ALL NOSE AIR has to go through radiator.

Then cut away all bottom trays so that there is no resistance to flow exit. Or run with no hood. Or cut big ass holes to reduce resistance. If you're talking about increasing radiator flow, I'll still wager that big ass vent holes will be more important to flow than louvers because we're talking about high pressure exit.

Again, like an exhaust, you want a wider orifice rather than flaps.

If you're talking dual purpose for aero, fine.

But I still think big ass hole will be better than louvers for increasing flow through the radiator.

And if the radiator isn't completely sealed on the sides and underside, then you're losing more cooling than the louvered hood buys you.

Heck, rather than hacking the hood, why not enlarge the nose hole to allow more flow in?

CKit

Here's a picture of what LJ from Full Blown did for us:



All air that goes through the nose either goes through the radiator (above) or intercooler (separate channel underneath. No leak around the sides. Like ram air.