DrZ1

Had been wanting to vent the underhood temp for a while and since this car won't hopefully be driven much in rain, as it won't be a DD anymore, I started looking for a solution. Long story on how I got in contact w/ someone who is interested in building a custom vent.

Following is the specs and link to a style that is closest to what I will be interested in.


Aluminum frames are waterjet cut out of 12 gauge (.0808") or 14 gauge (.0641") for strength & durability

All vents are skinned with PVC coated mesh that is UV Resistant with a High Tensile &Tear Strength

http://webhosting.web.com/imagelib/s...w&title=Arctic Cat M series Side vent kit


SO I mocked up a design, and wanted to get some comments on it. It is rough, but needed a starting place, I wanted more framework to help w/ strength. I plan to have one on each side.

If anyone else is interested, may be able to get a good price for making a small batch.

Steve

Van

I'll give you my thoughts, for what it's worth...

First, move them more forward - you need air going over them to create the low pressure to pull the hot air out. The closer to the windshield, the less effective they'll be because you have air separation from about 1/2 way up the hood to about the middle of the windshield.

Make them wider. You have the the stiffening channel on the outboard side, but I think you can go to the bend in the middle of the hood. That might also help you blend them in.

And, finally, make the scallops stick up above the hood. I've seen some where the scallops (bent fins) stick down - but then the air has to take an S turn before being vented out.

George D

This is what we did with my hood. We also have a added a different splitter and my belly pan has vents.

Good luck with your project. My vents and splitter are manufactured by http://www.deutschnine.com/.

Grandpa#3

Back in the 50's we had louvers stamped in the hood of our cars in California. We thought it looked sharp, and it did lower the engine compartment temperature. The louvers were 8" long and we did rows of six each, two to three sets per side. It depended upon type of car and how much we wanted to spend. We did a lot of customizing back then in High School. Our Machine and Auto Shop Teachers were both into customizing students cars. The stamped louvers look much better than an add on pasted onto the hood. Different times I guess, but both gets the heat out of the engine compartment and that is the main thing.

Cheers,
Larry

TurboTommy

Is there any literature anywhere, or a thread, about tests done how the air flows through the engine compartment at highway speeds. How bad is it, really? Porsche thought of alot of things when they design their cars. I can see soaring underhood temps in stop and go traffic, but when driving at highway speeds there must be decent underhood temp evacuation, no?

DrZ1

Thanks for the help,

I am unfamiliar with the dynamics to have effective heat transfer out of the engine bay. I assumed, wrong of course, by having the vents, the hot air would easily be pulled out.

I will definately move them down and make them a bit wider. I would like to keep them on the outside of the hoodlines. Unless that area is too ineffective. In that case would it be better to have two towards the center of the hood?

Steve

JohnKoaWood

+1.....See pic, it is of a 924, but is effectively the same for this purpose... the HIGHEST low pressure zone ends just after the strut tower (tower being around point 15, negative pressure ends at point 17, or just in front of the rear end of the tire!), making positive pressure from there back, and spiking at the windshield...

FWIW, on my 951 I am considering 2 WIDE vents at around point 11-12 and louvers from 16 forward on the outside of the hood, to the underside of the hood but facing forward.... much aft of that is counter productive, and the wide ones behind the radiator will capitalize on the highest negative pressure zones...

Van

I think keeping them toward the sides is OK - remember where your headers and turbo charger are... very close to the shock towers.

Tommy, all I can tell you is that it's cookin' hot under the hood of these cars... and that's at track speeds (average ~80 MPH). I'm not aeronautical engineer, but it seems to me that the air flow through the engine compartment is designed as such:

Air enters in through the radiator and intercooler. The bat wing/belly pan forces air under the car that creates a low pressure area behind the engine cross member. This low pressure area helps draw the hot air, that just went through the nose of the car, out of the engine compartment. Up towards the shock towers, air is primarily stagnant due to the limited clearance and limited venting. (I see dust collect up on the shock towers, which supports this theory.)

Air, being a fluid, likes to "stick together" as much as possible when traveling over an object. The air is pushed aside by the nose, and what doesn't go through the radiator/intercooler, is pushed over the top of the hood. The air tries to make a semi-straight line from the hood to the windshield and over the roof of the car. This leaves a turbulent, low pressure area at the bast of the windshield. Although it's low pressure here, it's cool and perfect for the blower fan to pass into the cabin.

gt37vgt

I agree ..I've given this a lot of thought and to me the most logical bonnet vent is rippered strait off from ferrari Daytona. I think it would be pretty easy to do with the bonnet sheet metal.cut a U shape (strait lines) in the bonnet push the panel down and weld 2 thin triangles either side .
also i think over the strut top is about right .. i think it would be just forward of the high pressure wake from the windscreen and there could be a high pressure spot forward on the bonnet as the bonnet face curves down .
I thing i considered was cut an inch off the side of the bonnet then mount some lovers were the guardd screws on...
An in a mesh inset type like that be sure to use that mesh is directional the type that would scoop ait in or draw it out depending wich way you put it ..

gt37vgt

ah tis is the stuff i mean http://www.google.com.au/images?q=ex...bs=isch:1&sa=2
yeh i refer than off to the side's as well . less effect on the down force generated by the windscreen and posibly less drag as the thinner heated air gos over the draggy side windows

David Floyd

5" was the largest die my local Hot Rod shop had

JohnKoaWood

And we (or it could just be me) are all in LOVE with your hood David...

Bri Bro

David, have you tied some string on the vents to see if air is going into or out of the vents? It looks like the air should be going into the vent from the diagram.

David Floyd

Not got around to the string, will give it a try this weekend.

Louvers are in the 15-16 zone on above graph, have been told that with the gills being raised on the hood will actually create its own draw

ehall

David, what do you do about the heat affecting the paint on the hood?