Engine compartment venting

[Todd in Vancouver]

Hope this is the right section for this but please move this post moderators if you feel it's in the wrong area.

So, I'm part way though mark Stielow's Pro-tour book and have also been reading many of your different posts on-line here on Pro-tour.com. I do not have the mathamatical knowledge or education to totally figure this out so that's where all of you come into play and school someone like me :)

I have a 1967 Camaro and I noticed that Mark cut two huge vents in his 67 hood for, what I understand, venting of the air coming into the front of the car so it's not lifting the front of the car as it accelerates. I'm sure there is better terminology but hey this is the best I can do. I also noticed the same on the One Lap Camaro but I don't want to post any pictures without the owners consent but I'm sure all of you know what I'm talking about. Now, if I'm not mistaken the late 70's/early 80's Camaro and T/As installed the fender vents for the same reason to help keep the nose of the cars down at higher speeds.

Now, the first thing that strikes me is the size difference between the two. I'm sure there is a mathamatical formula for figureing this out (enter the people smarter than myself) to sort out how big a hole one needs to cut into the fenders or hoods to let the air out so the front of my car doesn't try to fly away while I'm driving at high speeds. Yes, I plan on running this thing all out or I wouldn't bother building it.

So, why am I asking this? because I have an original steel SS hood and there is no way I'm going to cut huge holes in the hood like Mark and One Lap did. But, at the same time I really can't picture installing the later Z28/TA fender vents on my 67. So, what I was thinking was, to take the original '67 grills out of my hood and modify them so they are functional, or even take a set of '68 repos and hack open the 3 big stacks and let that air flow. Question, will doing this make any difference or is it just not enough volume of air to bother? Is there a down side? Has anyone already tried it?

Please feel free to laydown the facts, but please dumb it down for those of us who don't have advanced degrees in math.

[Ron.in.SoCal]

There are way smarter people than me on this board to answer this...

Todd...great queation. The mathematics of aero is called CFD - computational fluid dynamics. Complex subject. To the best of my knowledge (not much) no one has put a first gen through a wind tunnel and even little changes can make a big difference. The other approach is a share-ware software program (simulator) or using string as you drive down the road.

To maximize available traction, the two factors at work here are lift and drag. What you're trying to combat is lift and from what I've read side vents will do a better job than hood vents. There are waaaay more factors involved than just the previous statement: how air flows through the front of the car, what you do to redirect it (radiators, shrouds, brake ducting, etc.). The other way to combat lift is via downforce. This is why you see splitters, underbody panels, rear diffusers and rear wings.

Applied properly, downforce trumps drag nine times out of ten.

I'm just getting started, but I'll defer to guys w advanced knowledge and have done testing to follow up.

James, Carl, David, Ray (?) step in here :cheers:

[Y-TRY]

They also did the same thing with the Mule. Forgive me if I'm wrong but I'm pretty sure the purpose in all 3 cars is heat extraction.

I'm looking at doing the same type of thing on my '68 to vent some of the heat from the turbos. It gets hot in there.

I've seen where old mopar NASCAR cars would vent from the fender into the wheelwell to create downforce but I don't think that's the intention with these Camaros.

[exwestracer]

As you might think, how effective the vents are depends largely on WHERE they are located on the hood. Here's a "generic" CFD of a NASCAR Cup car, (yes I know a Camaro would be slightly different) and you can see how the air pressure goes up (redder shade) closer to the base of the windshield.
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Seems like the best place to vent the hood would be ahead of the front axle centerline; but, the entire hood surface is below the pressure entering the grille. It also seems like a wider (side to side) vent would be of more benefit than a longer (front to rear) design. THAT would ugly up the hood of a first gen pretty quickly!

[cornfedbill]

Yes, Ray is correct as usual. He knows his stuff.

If a vent on top of the hood is too far back the flow will be from the hood down into the engine bay. This would have the opposite effect on downforce and would tend to lift the nose at speed. Any vents on top of the hood need to be far forward to take advantage of the low pressure zone at the front of the hood.

The NASCAR model in Ray's post shows a pressure rise at the base of the windshild. Your 67 has much less slope on the windshield and thus a much larger high pressure zone that you will need to avoid.

The wide vent in the hood that would work best - see the C7 Corvette or the Pratt and Miller C6 GT2 racing Corvettes - would not look as good on the hood of a 67 Camaro. Fender vents may give you the look you want. See the Pumpkinator for another option. The C2 and C3 Corvettes had low vents, but also more fender length for them. I don't think you will have room for low mounted fender vents.

I am planning one vent in the center of my hood in front of the cowl scoop that will be just a bit like the hoods on the 68 and 69 L88 Corvettes. I plan to add some ducting underhood to turn the air up through the vent. We will see how it turns out.

Good luck.

[silvermonte]

I was just wondering this exact same stuff the other day, only im wanting to do this with a s10 that has the aero of a barn door, so i think its a fairly lost cause

[Todd in Vancouver]

Great input and thanks for all your ideas. So, if I understand correctly the "vent holes"need to be as far forward on the hood as possible like on the One Lap car, the Mule and Mark Stielows last build on his '67 Camaro. Actually I went back through his book last night and it appears that when he added the twin turbos to the Mule he added louvers to the front area of the hood. I'm thinking of adding these ones to my SS hood.
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What I'm not clear on though is this just for heat reduction or/and does it have any effect on the stability of the car at higher speeds?


Hope I'm not upsetting anyone using this picture it just happens to come up under Google images and shows what I'm trying to explain.

[Y-TRY]

Big Red doesn't have vents.

[cornfedbill]

Big Red doesn't have vents.

Big Red is a high speed open road racing machine that was purpose built. I wonder how the cooling would be in lower speed competitions like autocross.

That is a good point to think about.

[Tom Welch]

The 67 Firebird we are building has had fender vents installed behind the ft wheel opening. I think it looks appropriate and should help to some degree with underhood heat/pressure

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so much for posting pictures.

[James OLC]

The high pressure zone extends much further forward on a first gen then on the cup car shown. Venting the hood on a first gen is complicated by three things - the rad support is "so far back" from the front that it eats up a bunch of the realestate that you want to use, there is not much room between the rad and the front of the engine (this is complicated if you have an LS based engine, easier if you have a carb), and the grill opening area is so disproportunate to the radiator size so you tend to bleed air anyways if you are not proactive about it.

On the OLC we currently have:
https://static1.pt-content.com/images/noimg.gif

We have ducted the radiator in the front and will be plugging the balance of the grill once we confirm that we have enough air flow. We have radially changed the shape of the lower fenders behind the wheels to evacuate air. And we have added the hood vents.

We had planned to (and still may) add vents to the top of the fenders but that will only address air in the wheelwells. At one point we had planned to add a vent behind the wheelwells but while that usually looks great in renderings the fact of the matter is we have tulips back there that are right in the way of everything.

Ultimately you have to ask what is your goal with the hood vents - better aero? better cooling? required cooling (i.e. turbos)? The answers are not mutually exclusive but you might find some require more work/dedication than others.

[cornfedbill]

James,

Thanks for that information. Although I tend to learn most from my own mistakes, it is much less painful to learn from the wisdom of others.

[Todd in Vancouver]

James thanks so much for sharing your thoughts with all of us. As you stated, ultimately everyone will have a different need to fill with this. Personally, I will need to drive my car for a while to see what I need in regards to this venting. My initial desire was/is that from memory the last time I drove a car like this at high speeds it had a tendency to lift in the front and the steering seemed to be "loose" the faster I drove. From what I understand I need to vent that air to get the nose down, but, until I drive it I have no idea how hot it's going to run etc.

When I started this thread I spent a lot of time looking at Jame's car build along with others and trying to understand what everyone did and why. I really appreciate your input and look forward to seeing your car at some future events. I also get to Alberta often so maybe I can even see it at home here in Canada.

[astroracer]

Another "venting" option to concider is building a front airdam (Similar the OLC) which will extend back, under the radiator, creating a low pressure zone somewhere behind the radiator support. This low pressure zone will help pull air through the radiator and direct it out under the car. There is a lot to be said for belly pans and aero tunnels at the back of the car also as they both help clean up the underside which smooths airflow and improves "draw" from the engine compartment.
Mark

[Tom Welch]

James, can you show us some pictures of how you modified the fenders behind the wheel opening? I would really like to see this modification and gain some knowledge here.

[cornfedbill]

Another "venting" option to concider is building a front airdam (Similar the OLC) which will extend back, under the radiator, creating a low pressure zone somewhere behind the radiator support. This low pressure zone will help pull air through the radiator and direct it out under the car. There is a lot to be said for belly pans and aero tunnels at the back of the car also as they both help clean up the underside which smooths airflow and improves "draw" from the engine compartment.
Mark

Back in the days of IMSA inspired cars and expensive gasoline, I had a Vega with a large air dam I fabricated. I used rubber flashing supported by flexible fiberglass to get the nose about 2" off the road surface. I used ducting up the the radiator below the bumper line (the bumper was actually removed) and sealed the radiator inlet louvers. I was amazed at how well it sucked to the ground.

In fact, I often drove with the rear opening hood open to allow better cooling on hot days with the 12" square radiator. At speed it would compress the lift spring until it was nearly completely closed. There was no actual venting in the hood or fenders.

That solution just prevented air from entering and created a low pressure zone below the engine compartment so the air exited the underside.

It was crude, but very effective.

[James OLC]

James, can you show us some pictures of how you modified the fenders behind the wheel opening? I would really like to see this modification and gain some knowledge here.

Sure - give me a bit of time and I'll post something up.

[novaderrik]

i didn't use any mathematical formulas- hell, i don't know if they even do any good- but here's the fender vents i put in the hood of my 86 Camaro.. you can see quite a bit of heat radiating out of them at stop signs when the electric fan kicks on...


https://static1.pt-content.com/images/noimg.gif

and, yes, they are heat register covers that i got from Home Depot.. and also notice how far back they are- the front edge of the vent is about an inch back from the radiator support.. they'd probably be more effective if they were up closer to the leading edge of the hood, but this was as close as i could get them without making up some fancy ductwork or something under the hood..

here is a closer look at some of the other supporting aero mods i've done to the car... it's no longer a "bottom breather"- all the air that goes thru the radiator and into the air intake goes thru the grille and is directed to the proper places with an airbox made out of coroplast... the car kept it's cool and the carb was kept fed with cool air thru the open part of the grille way at the bottom that doesn't have the duct tape-oops, i mean "racer's tape"- on it.. i'm sure the hood vents allow me to get away with a smaller opening, which also helps the aero of the car in addition to the venting of heat. taping off most of the grille gained me 2mpg...

https://static1.pt-content.com/images/noimg.gif

the beauty of owning a POS is that you can do fugly stuff like this and see if it has any benefits...

[MonzaRacer]

air routing is key thing. IF you actually look at Corvettes, gen3/4 F body, GM used high air flow down low, pushed it up and through a/c, rad, coolers and such then back down and under car for majority of cooling. air actually had to climb the mountain then run down it and under car. Now why did it work, well aerodynamics of the car were so that they created a LOW pressure area UNDER the car both for handling AND,,,,,,,,cooling. I worked a dealer and we got several of the GM bulletins about how aftermarket noses messed up the cars air flow, namely causing over heating or increasing the running temps and burning up trans. As for cooling a car also dont look past BETTER coolants like Evans NPG+. Another trick to limit UNDERHOOD heat is using thermal barrier coatings on headers and even your block and heads. when working on a kit car for a guy he had bought an old bread oven to cook paint and help clean stuff,,amazing how a good 500deg broil will cook stuff off to point a wire brush is all you need. We actually coated the OUTSIDE of his block and heads and underside and top side of intake. Normalizing temps helped a lot in tuning. We even did barrier inside exh ports and valves, used a slicker type coating inside and on metal parts like bearings, springs etc. Triple coating the tops of pistons, the dry film on sides of pistons. All baked on. We got engine compartment temps down to very little and he used a 4th gen Camaro cooling unit(condenser/rad) and set at similar angle, and ducted air down. We had air damn under rad, but lower than splitter/nose. Worked well with 427 sbc and 24x16 aluminum rad and Evans NPG+ but even better with Camaro rad,when we went back with air cond.

[Todd in Vancouver]

Another question but along the same lines.

I'm taking the hood in to get sandblasted in the next couple weeks with any luck and I've decided to copy the vents that are in the Mayhem hood. Can anybody enlighten me on who might do these kind of metal work and install punch in these louvers or sell them and I can weld them in?

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[Greg from Aus]

Mark's is a Carbon fibre hood.

Greg

[jlcustomz]

There are sources that sell prepunched louver sections that you can cut out & weld in.http://www.google.com/#q=universal+pre+punched+louver+panels&hl=en&ei=rjtuUfnKAYqs8ATxxoHoBQ&sqi=2&start=10&sa=N&bav=on.2,or.r_qf.&fp=bbbe49cbf7317589&biw=1920&bih=954 There are factory versions worth considering, such as old Z-cars.

[Ron.in.SoCal]

Worth a look:

https://www.anvilauto.com/product_detail.php?product=hoodvnt_1

[LS1-IROC]

Any idea on how to keep the rain out of the engine compartment when you install vents? I wonder if the vents from the factory have some baffle box under them to help with water management?

[hotrod56]

What about moving the radiator to the back and blocking off the space? Kills 2 birds with one stone - aero and weight. Oil, power steering, and AC parallel to the ground in front with fans or filled by small front vent that is exhausted or exits below the car? Thoughts?

[H2Ogbodies]

If you plan to do some extensive hood mods for heat extraction and gain some front down force at the same time, take a look at the early 2000's Mustang Cobras. A friend has an 03 and it has a very tastefully factory Cobra with the hood having a wide air inlet and the airflow exits through the base of the hood below the windshield-thus taking advantage of the high pressure area which literally creates a vacuum effect underhood @ high speeds. Ever see the DOHC 4.6 motors? That's a lot of motor sitting in that engine bay.

[JEFFTATE]

I always wanted to make the cosmetic louvers on a '68-'69 Camaro SS / raised panel hood functional.
Duct them up to the radiator as a heat extraction source.
But I think they are too far back on the hood .
Higher pressure at the base of the windshield would push air into them ( I think )

[cornfedbill]

I really like this Monza. The new hood has a lot of venting for the radiator. I plan to copy this to some extent.

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[Dr G]

This is an old thread, but I just saw it. Fun subject though. I was real big into this back in 2003, when I owned an E30 M3 BMW.

I installed a hood vent on that car, after doing a ton of research trying to figure out what to use for a vent and where to locate it. My purposes where both better cooling and reduced lift. At that time I was considered a little nuts for trying this, but since then a lot of others have done it in that community.

https://static1.pt-content.com/images/pt/2015/04/pic1-1.jpg

https://static1.pt-content.com/images/pt/2015/04/pic7-1.jpg

https://static1.pt-content.com/images/pt/2015/04/pic2-1.jpg

I wish I had the capability at that time to properly duct the radiator air up through the vent. That would have been the right way to do it. The car also had a splitter and venturi under tray to reduce front lift. That was factory BMW stuff you could add.

The theory for adding a hood vent is that air builds up against the rather blunt front end of the car, causing local stagnation and high pressure. As this air sweeps up over the front end of the hood it detaches, creating a low pressure zone that you want to leverage for air removal. The air then hits the front windshield creating another high pressure zone at the cowl. This zone is sometimes used to push air into the engine inlet.

I would not personally want to use the low pressure zone underneath a moving car to help exhaust radiator air, as this will reduce the low pressure and lead to lift. Manufacturers used to do it this way because it was easy and cheap, many still do. Most folks would not really understand a hood vent in their Camry or Civic. Side skirts let's remember are an effort to reduce air from leaking into the low pressure area under the car. You really only want air from the front of the car to travel under the car, and then ideally out the back via a diffuser to slow it down a bit before exiting.