Hood Vent Placement - Autocross Camaro Edition

There is already a great thread on placement, but since these things are often very vehicle or situationally dependent, I decided to fork off and create my own thread.

I have some hood louvers from Trackspec Motorsports.  The intent in installing these is to help get hot radiator air out of the car, and provide a small aerodynamic benefit.  For the time being, the radiator WILL NOT be ducted to the hood, but that may eventually happen.

The location of the center louver is basically in a fixed location.  It's placed between the radiator and the air cleaner/cold air kit I made.

The center louver is 200sq inches.

So, now that we have the center location established, I have two other louvers.  This is where the placement questions start, and me guessing at how things works beings.  I'm likely wrong.

OPTION 1 - Here is the first idea, which has largely been rejected for aesthetic reasons.  Granted, it would make eventual ducting from the radiator the easiest.

OPTION 2 - So the next placement sets the other louvers out wider.  A little harder for ducting, but not impossible.

OPTION 3 - Some other folks, like Apexcarver, have suggested moving the outside louvers back.  The idea would be to help pull heat from the headers out of the engine bay.  I don't think I have a heat issues now (car is comfortable to be in for races, nothing looks "cooked," etc) but, as has been said, just because I don't notice a problem doesn't mean there isn't one.

One other consideration with this placement is the factory fender vents on the car.  I'm not sure what sort of impact placing these louvers further back will have on those.

So I again come to you, the smartest people on this sort of thing that I have available to me, to point me in the right direction.  I'd love ot hear your thoughts!  Thanks.

Part of my thinking is that this is an autocross car.  Direct heat venting pathway near the headers will serve good purposes whether the car is in motion or not. Cooler general underhood temps are pretty much always a good thing. Opening the hood between runs is impractical due to how its attached to the car.  

I think it could also be said that you arent adding the vents to fix an overheating problem, at least not at this point (new rad, new fan setup, etc), but for general improvement. 

Apexcarver said:

I think it could also be said that you arent adding the vents to fix an overheating problem, at least not at this point (new rad, new fan setup, etc), but for general improvement. 

 

100% accurate

My initial thoughts were the same. On an autox car, you're probably more concerned with engine bay heat soak between runs than trying to improve airflow through the rad during a run. So get them above the headers.

Someone smarter than I might correct this, but I suspect that if your goal is decreased lift on the hood at speed (ie, more front downforce) you'd want them fairly far forward, maybe under the bow wave behind the nose.

Keith Tanner said:

My initial thoughts were the same. On an autox car, you're probably more concerned with engine bay heat soak between runs than trying to improve airflow through the rad during a run. So get them above the headers.

Someone smarter than I might correct this, but I suspect that if your goal is decreased lift on the hood at speed (ie, more front downforce) you'd want them fairly far forward, maybe under the bow wave behind the nose.

They are good thoughts, and I haven't really been thinking about the specific needs of an autocross car and have just been focused on the biggest aero benefit.

As far as moving them forward, there is so much dead nose space in this car infront of the rad, but putting anything there would just hurt cooling.

A new contender?  How important, for heat soak reasons, would it be to place the vents directly over the headers vs off to the side a bit?

And here is another.

Robert Lewis, who knows a thing or two about building a CP car, suggested this:

"You don't want them that close to the windshield, pressure at the base of the windshield will keep them from working.  A good place for the small ones is above the inside of the front tire towards the rear, but at least 15" from the windshield if you don't want/need to put them at the front"

I really like it.  Thoughts?

On any car I've tested, there's basically a V of low pressure on the hood. It's highest pressure in the center and at the base of the windshield. If you think of how water flows off a submarine when it's near the surface, you get the idea :)

More applicable, here's some actual pressure measurement on a Miata. These are relative numbers, so don't get wound up on units :) You can see the trend - as you go back, go sideways. This is based on dynamic airflow, of course, not heat escaping while parked. But I think your most recent layout is pretty solid.

Hey - not to hi-jack this thread, i am currently doing the exact same thing on my Camaro, so this is great - i was going to use backwards NACA ducts - is there any thoughts to the relevance/experience/info of running NACA ducts backwards (in the same approximate locations as the outside smaller vents shown here) as used for venting?

Thanks!

Matt said:

Hey - not to hi-jack this thread, i am currently doing the exact same thing on my Camaro, so this is great - i was going to use backwards NACA ducts - is there any thoughts to the relevance/experience/info of running NACA ducts backwards (in the same approximate locations as the outside smaller vents shown here) as used for venting?

Thanks!

I don't know the answer, but welcome!  Continue to ask away.

NACA ducts (aka "submerged ducts" or "submerged inlets") rely on vortex generation to work, that's why they're a very specific shape. You cannot turn them around and use them as effective exhaust vents. They are an inlet only. 

The coolest thing about NACA ducts is that the information is public.

https://ntrs.nasa.gov/citations/20090012113

Thanks - and thanks again!  i was looking at the old shelby GT350 hood, naca ducts up front, open vents in-line at the rear. except instead of using the naca ducts at the front, I'm looking for a viable exit point (like Gimp) and wondering in the shape worked the other way - super glad you cleared that up in a hurry!!

In reply to Matt :

Just for clarifications sake, I'm not running NACA ducts.  I'm running louvers.

https://trackspecmotorsports.com/universal

So, I think you would pull more heat *radiator* with Option 1.  Also, with them all in that area you should be closer to the lower pressure sections of the hood.  Keith's note on teh NC there kinda falls into all the others I have seen or mentions of it.  This should get you the max downforce from the front too.

Your Fender flares look to be designed well, and you have a side vent, if you can also or rather cut the fender and roll it in to make a smoother area and open up to the underhood area, that would suck the rest of the heat out really.

In reply to Gimp (Forum Supporter) :

ya - i read that back and changed the wording!!

ps: I Love the Trackspec hood vents - i had them on my 3rd gen!!

Thinkkker said:

Your Fender flares look to be designed well, and you have a side vent, if you can also or rather cut the fender and roll it in to make a smoother area and open up to the underhood area, that would suck the rest of the heat out really.

 

 

Thank you!  I'd love to do what you mentioned with the fender, but as I read it, that's outside the ruleset.

I'd love to see a full shot of this car, it looks burly.

The splitter and flares are getting a revision as we speak, but here you go!

That is acceptable 

so, I'm kinda surprised nobody's mentioned this... but, imho, you don't want to put in that central vent.  Otherwise, you'll start to suck hot radiator exit air for your engine intake air, once you start moving.  The only way I'd suggest putting a central vent ahead of the intake, is if it's on a push-pull cable... and it's "open" while sitting and "closed" while on a run.  But, I suspect that'd be protested as some kind of "moveable aerodynamic feature".

Generally, though, I like the side vents set further back.  Or, maybe cutting the big central vent in 2 pieces, and putting them back in the corners.  You might also consider trying to 'seal' the sides of the riser hood up against the 'glass' to minimize the chance of hot air escaping out the side vents getting pulled into the engine intake.

I assume that radiator fans are the only allowed 'fan type device' allowed under the hood?

sleepyhead the buffalo said:

so, I'm kinda surprised nobody's mentioned this... but, imho, you don't want to put in that central vent.  Otherwise, you'll start to suck hot radiator exit air for your engine intake air, once you start moving.  The only way I'd suggest putting a central vent ahead of the intake, is if it's on a push-pull cable... and it's "open" while sitting and "closed" while on a run.  But, I suspect that'd be protested as some kind of "moveable aerodynamic feature".

I'm glad you brought this up.  When I was researching this project, I had a similar thought.  I took all the time and effort to seal the intake to the hood so that the engine only sources air from the cowl induction opening, would I be going backwards by venting hot air a few feet in front of it.  I will make an effort to find my sources, but generally speaking, those with better testing rigs and more data than me felt the impact was minimal.  Basically, a lot of air is getting mixed, and while some of the air coming out of the vent will mix with the outside air, it's not enough to make a real impact on intake temperature.  I should be able to test and confirm this by blocking off the vent and logging IATs.

I also suspect you're right about a "moveable aerodynamic feature" interpretation.

sleepyhead the buffalo said:

Generally, though, I like the side vents set further back.  Or, maybe cutting the big central vent in 2 pieces, and putting them back in the corners.  You might also consider trying to 'seal' the sides of the riser hood up against the 'glass' to minimize the chance of hot air escaping out the side vents getting pulled into the engine intake.

I'm not sure what you mean by "trying to 'seal' the sides of the riser hood up against the 'glass'" bit.

sleepyhead the buffalo said:

I assume that radiator fans are the only allowed 'fan type device' allowed under the hood?

The rules only mention radiator fans, so I suspect that's a no-go too. 

Anecdotal - but Miatas pull their interior air for the HVAC from the base of the dashboard. It's always a little warmer than ambient. Running a vented hood makes warmer. This is again based on dynamic airflow only.

I'm assuming this car doesn't pull timing in response to IAT?

In reply to Keith Tanner :

That's good info for sure. 
 

As far as pulling timing, it is capable of doing that, but I have adjustment over it.

Gimp (Forum Supporter) said:

sleepyhead the buffalo said:

so, I'm kinda surprised nobody's mentioned this... but, imho, you don't want to put in that central vent.  Otherwise, you'll start to suck hot radiator exit air for your engine intake air, once you start moving.  The only way I'd suggest putting a central vent ahead of the intake, is if it's on a push-pull cable... and it's "open" while sitting and "closed" while on a run.  But, I suspect that'd be protested as some kind of "moveable aerodynamic feature".

I'm glad you brought this up.  When I was researching this project, I had a similar thought.  I took all the time and effort to seal the intake to the hood so that the engine only sources air from the cowl induction opening, would I be going backwards by venting hot air a few feet in front of it.  I will make an effort to find my sources, but generally speaking, those with better testing rigs and more data than me felt the impact was minimal.  Basically, a lot of air is getting mixed, and while some of the air coming out of the vent will mix with the outside air, it's not enough to make a real impact on intake temperature.  I should be able to test and confirm this by blocking off the vent and logging IATs.

I'd be careful with the sourcing on this.  If it's "race car" stuff... keep in mind, they tend to get "more longer/faster" straights in which to get the mixing.  Whereas, you'll have lower speeds, shorter bursts of high speed... followed by heatsoak.  Do you have a way to, (and if so, have you), log IAT's during runs?

It's possible, that with a "high enough" front vent angle, the flow is going to get pulled out and land mid-way up the windshield, and cooler air is going to get sucked in/around underneath that warm exhaust air.  I should go back and look at some of AJHartman and RaceLouver's tunnel smoke... although, I suspect they're testing at 100mph, not 60mph.