spdracerut

The 2nd attempt is doing exactly what you suggested isn't it?

For the cost of 'free', seems pretty good.

You mean like this done three years ago?

http://www.motoiq.com/MagazineArticl...erheating.aspx


And if you look at the front of the hood, it has a pseudo cooling plate built-in.

Well, there's always the trade-off between cooling efficiency and drag. No undertray and hood would really jack up your drag. You do realize that the openings created by the flaps is very nearly the same area as if you just cut holes right? If actual louvers were custom designed, the area would be the same.



Riddle me this, why do so many race cars use louvers to help evacuate air from unducted areas such as engine bays and wheel wells if just a big opening is better?

The only time I see just open holes is when the heat exchanger is fully ducted to the hole like Scandinavin mentioned; the air only has one place to go which is out the duct and the hole. If no duct, it can circulate in and around the engine bay:


As for your exhaust example, there's a huge difference. The engine is pushing the exhaust out and the engine is a pretty strong pump. For airflow pushing air through the radiator and engine bay, there's just the stagnation pressure of the air pushing it through. To make an electrical circuit analogy, the air pressure is voltage (V), the mass flow of air is current (I), and the resistance R is everything restricting the air flow(radiator, oil cooler, engine, air box, steering rack, everything in the way between the hole in the nose and any escape path out of the engine bay). From school back in the day, V=IR. Voltage is a constant that's determined by your driving speed. So for a given voltage, your flow is dependent on your resistance. Increase resistance and there's less flow. Decrease your resistance (venting the hood), and flow increases. Based on the theory presented, the louvers will reduce the resistance more than just an open hole.


So... present some theory, science, or real world examples to support your thought.

CKit

I don't think the 2nd attempt is doing anything functional at all really. And that the topic starter didn't have the foresight to think about that before hacking it up for the holes makes me think that everything is piecemeal afterthought rather than a cohesively planned build.

My time is not free and the mish-mash build isn't convincing enough to make me hack up a hood in that way.

Yes, but not as efficient as a secondary cooling plate. And if you're trying to convince people to hack up a hood, you better have done EVERYTHING possible to get more cooling through the radiator.

Yes, but the current "free vent mod" cuts three holes per side which is more area than the two louvered holes plus center slat. Compared below, look at the difference in surface area.



So riddle me this? Why not just duct the radiator to a big center slat? Air in through ducted nose, and then back the radiator before the air hits the engine. Keep the flow laminar and vent it up and out to a similarly sized center vent. You can louver the leading edge if you like.

It'd take less time and effort to do that then cut little separate side louvers. Use some scrap aluminum and foam and there you go.



The theory is that six big holes are better than two and a half smaller louvered holes.

Like I said, why not just duct the back of the radiator, too and vent that out to a big, flat center vent. Louver the leading edge if you like.


And hey, here's a thought! Get rid of the AC condenser blocking the radiator before hacking up the hood! Bingo! Improved air flow.

If you like using race examples, then find me a race car with AC.

It's again that weird mish mash. Cut hood + scraps of fire blanket? Trying to get better flow through a radiator, but blocking it with an AC condenser?

Is it a street car? Is it a race car? Is it a street car trying to be a race car?

It just doesn't seem purpose built enough. And to rock a hood like that, it'd have to be super hard core built for me to not be embarrassed.

It's like putting titanium lug nuts on steel wheels.

CKit

For the Subarus, they vent the engine bay out the fender vents out both sides. Structural slats, but not louvered.

For rear engined cars, surface area predominates. Slats are to keep flow laminar, rather than a frank louver to lift flow. All the black mesh is vent.




I'm not arguing that louvers aren't useful. I'm saying that I don't think a few puny louvers are going to make up for only having those small cut outs. Louver all six panels and get rid of the AC and you might be in business. But for simplicity, I'd just do the six cuts and use rubber trim strips to help either with leading edge or lagging edge.

Or get some cheap aluminum duct work and vent the backside of the radiator out to a big center cut. Louvers optional.



For some reason, dubiously functional stuff on street cars that look amateurish walks a fine line between race and rice.

Not saying that it doesn't have some function, but not nearly enough to justify what it looks like for me. If other people like it, great. But throwing out some high school physics equations doesn't mean it's cohesively engineered.

I'd take out the AC or duct the back of the radiator to a center hood vent if I needed more cooling before making the car look like that.

Removing the AC will do more for radiator airflow than the hood vents (I think) and it's also a "free" mod.

Actually, now that I think about it... the cheapest, easiest and most effective hood venting mod would probably be to remove all the plastic shrouding up by the windshield wiper so that the airflow could come up and over the windshield. If you could use a longer hinge or spacers to lift the tail end of the hood 1-2cm up you'd get crazy good airflow through the bay.


For the record, I think the louvers are "fine" and if the thread was, "hey, I had time and was bored and made some slits in my hood because I think it's cool" I'd be like, "cool bro." But I wanted to bring out physics counterpoints and questions to the efficacy of this mod so that the casual reader would have a counterpoint to consider.

The comments on the original link basically echo the criticism in this thread. And did you really pay $200 for that hood just to do that do it?! That's not free.

ringo14

what is the hood insulation used for and why did you want to keep it ?

i was thinking of removing mine possibly

CKit

(CRs don't have it from the factory)

rhouck

I thought this had been tested previously and the pressure near the base of the windshield actually causes the opposite effect and does not work as desired? I thought I read something about this in the context of why (1) those hood spacers are a waste on our cars and (2) not to put hood vents too far back. I may be mistaken, however.

CKit

That could very well be possible. Anything can happen when starting to add aftermarket piecemeal hacks and parts. Who knows what the interplay between louvers and windshield are for that matter, too. Or how it works in relation to height of hood gap. Maybe hood gap would work if you sealed the sides? Don't know.

Which is why I wouldn't necessarily recommend any of it.

I'd think fully boxing the nose to increase laminarity of flow in would have the same effect (increased flow past the rad fins) as cutting the hood.

I'm confident that you could do that for less than $200 in cost (the cost of that spare hood).

I think boxing the nose and box venting the back of radiator + wide, flat center vent would be very effective and cost less than $200 and take less time than the multiple little cuts.

But then again, with an aftermarket rad, no AC and OEM hood, people have been able to keep water temps down to 180-190 so I don't really see the point to added rad flow.

Venting heat from engine bay to save shocks and rubber hoses, fine. But then we're back to bigger holes over louvers. Or bigger holes + leading lips rather than small holes with louvers.

One thing that the commenters on the original motoIQ thread brought up is that the louvers lose their effectiveness because they're cut on the sides. They'd have to be sealed there to get the real louver effect.

So again, a little bit underbaked and oversimplified of an original solution to a problem I'm not sure existed.

Just my opinion, but I feel consistent with the physics and relative contributions of each variable that I understand.

spdracerut

You do realize you can you can do the flap/louver method to those other holes too right? Last I checked, there's not some law of the universe preventing anyone from doing that. Though I question opening the rearmost opening as it's getting near the base of the windshield where there's a high pressure zone.

#1, because it's not a pure track car. #2 If you read the comments, it took less than two hours to do all the work. I imagine fabricating a duct going from the radiator to the hood would take as long if not longer. And that would require the stock air box to not be used, so some type of new intake would need to be made.

No, the theory is the louvered hole will extract more air than the big open hole when trying to help pull air out of a big, non-ducted, volume of space. Back to the previous point, nothing stopping anyone from making the flaps on the other holes too. Your comparison is about as relevant as comparing two radiators of high fin density and low fin density, but giving the low density one 3x the frontal surface area.

Because it's not a race car? You know, like the vast majority of S2000 owners who drive their cars everyday and like to track them on the weekends? And actually, A/C is required on GT3 LeMans cars along with the LMP cars with enclosed cockpits.

So what do you call the new C7 Vette or the ZL1 Camaro? Both cars come with oil coolers, tranny coolers, and rear diff coolers, and designed to be beat on at the track for 24 hours straight. That was a test criteria for both cars. Oh, they both have A/C. Are neither of those cars purpose built enough for you?

Oh, and about their hoods:

CKit

As long as it makes you happy, suit yourself.

Also note that none of their louvers are open on the sides and none of them rise above the plane of the hood.

CKit

I disagree with your pseudo-engineering. None of the examples you cite use louvers that look like yours.

If you can find examples of louvers that rise above the hood plane and are open on the sides, then I might buy your argument. But not with the hacking of the original build.

I'd say that was a waste of $200 and two hours.

Going with louver theory, I'd say cut out front four holes and make a recessed set of louvers out of wood or plastic if you like. Cover with a screen to make it look more finished. There are plenty of engineered examples of that.

So yes, louver theory.
No, hacked flaps that tuft up with open sides.