Venting the engine bay

[ACCLUDE91]

Yeah I dont get it either. There's just no way the air can flow in the same direction that the car is going.

think about a swirling effect. when the air hits the front of the car, it goes up and over, then hits the windshield and some goes up and over while some spirals and goes down and around or can be sucked into the engine by using a cowl ind. hood. They have been proven to work on larger flowing V8's but I don't think it'd be much gain on a little 4 cyl.

[trickedaccord92]

I saw a hatch once with a custom hood that was essentially cut perfectly for the intake fo;ter tp com half way out of the hood but he also had a fiberglass cover to enclose the filter incase of rain it looked really good i wish i could find a pic to show you guys

[owequitit]

Airflows from high pressure to low pressure.

Cowl induction hoods are actually very simple. The lower pressure caused in the cowl (or backwards scoop) by the engine sucking in air, causes air that would normally continue up over the windshield, to reverse direction into the cowl to try to equalize the pressure. The air flows backwards, the engine gets cooler air, everybody is happy. This is also why an improperly sealed cowl induction hood does absolutely nothing (the last gen Camaro SS comes to mind). If it isn't a total seal, the engine will not create enough low pressure to actually cause a significant airflow.

As far as venting your hood goes, it isn't going to make a significant difference on your car, so I wouldn't invest a lot of time on it. Spacing it might be OK, and putting something like a vented CF hood would be ok, but beware, that anything you do like that is going to create more drag, to almost no benefit. As it is, the engine compartment vents from below.

[Accord13&BA4]

To properly vent the engine bay, the best way to look at it is through the fenders.

Take a look at Z3 fenders with air vents. The whole purpose is to "vent" out hot air produced from all of the moving parts ie. motor.
I agree with OWEQUITIT, engine bay vents from below...so apply that to the sides: the fenders...

I wouldnt want to make any cuts or what not to my hood, i'd be too afraid of getting water and any other nonsense stuff flying into the enginebay...

Though, for track purposes that's all right, for a daily driver fighting everyday elements it's not suggested...

[perrero69]

i also hav another suggestion wrap ur header with that insulator crap. cus the header is one of the things in the engine area that gives off alot of heat

[owequitit]

I don't think the Z3 fenders will do anything, because the frame rail and inner fender structure is in the way.

The header wrap would help significantly though. Even the ceramic coating on my DC Sports VS the stock exhaust manifolds dropped engine bay temps a good 20-30 degrees.

[DilutedImage]

The wrapping or coating of the headers also causes the exhaust gases to maintain velocity longer, creating a smoother/more-effective exhaust system. .. Good stuff!

If you want to keep your engine bay cooler, just put the fan on a switch and turn it on.

[92DX]

I guess I'll just go with the heat wrapping the headers then, sounds like its the cheapest and most effective way of keeping the engine bay cooler, well at least so far it sounds like it.

But does enlarging the hood gap at the front a little bit would work?

[owequitit]

Increasing the hood gap is going to cause more adverse side effects than anything.

You car's primary source of cooling air is the lower grill in the bumper. I think the ratio is something like 80% bottom 20% top. Most Honda's are bottom feeders.

Anyway, by raising the hood in any way, you are disrupting the designed airflow. Honda spent a lot of time in the wind tunnel to perfect the airflow to the technological limits of the time (and believe it or not, the CB drag coefficient is lower than many newer cars).

While it may not seem like a large disruption, keep in mind that drag increases with the CUBE of the speed, so if you need 100HP to go 100MPH, it is going to take 800HP to get the same car to go 200MPH.

Even at highway speeds, this is going to have and adverse effect on passing power, accelerating ability, and fuel mileage because you are going to be using more of the available engine power just to maintain your speed.

Raising the hood in the front is going to have more of an adverse effect than raising it in the rear (think of a sail or parachute), and is not only dangerous if the hood pops open, but may also de stabilize the car to the point that it may become unsafe at higher speeds. Besides, how are you going to get it to latch?

All of this for a very small increase in cooling if any because most of the air will still be flowing out through the bottom.

One of the most common misconceptions I see about cooling, aerodynamics, and body changes in general is that people think that one small change will have a tremendous effect on the overall package.

There are very few aerodynamic changes that are going to have a substantial effect, the main one being a rear spoiler.

A rear spoiler (like the JDM flushmount) actually destroys lift by disrupting the smooth airflow over the lifting surface (the top surface of the car in this case), thus typically reducing drag in the process (one reason hybrid cars favor spoilers as opposed to wings).

A rear wing will generally help stabilize a car by creating downard lift (not the JC Whitney airplane wings you are thinking of, but the OEM style ones, or the ones used on ACTUAL racecars), but this also increases drag, as drag is a required by-product of lift.

Cooling airflow can have a substantial effect on overall drag on the car because it accounts for a relatively large volume of air. That is one reason they started venting it under the car. It does not really contribute to lift down there, and it is a natural low pressure area if I put a lip or airdam at the front of the car, so the air will naturally flow down and under the car. Since it isn't passing over the car, it isn't contributing to lift/drag as much, and is still flowing in the quantity necessary to provide cooling.

A good example are the engine cowlings on airplanes. They not only reduce drag, but also increase cooling flow and efficiency on airplanes, yet that is not what you would immediatly think, because it would seem that cooling would be less efficient than in the open air. That is not the case.

People usually think that a vented hood is going to help them a lot, or that a spoiler/wing will help them a lot or that this or that is going to make a big difference.

Aerodynamic improvements are usually about an entire package, not just one change. All elements must work together to acheive an overall net gain, with as little downside as possible. That is why race teams spend so much money on aerodynamics, especially in race series where HP rules limit engine changes.

Honestly, you would be better off getting some header wrap, a cold air intake, and maybe a phenolic intake manifold gasket if you can find one. Those 3 changes will provide a guaranteed net benefit by lowering your intake temps.

Raising the hood a little bit isn't going to blow your car up or anything; but why take a potential downside for something that may have little if any benefit, when there are cheap easy gains elsewhere?

[Spartan1987]

You can do it with skateboard washers or whatever or just shim it but you will need a longer bolt if you go that route and yes thats prob the cheapest way. I plan to do that in the future. Or if you wanna be ghetto cut a hole in your hood or just run without one.

exactly what we need, another ghetto ricer around town. hahahaha

[92DX]

Well I read it in a magazine, probably super street. They were talking about raising the hood gap around 2 to 4 mm. They said that more cool air will plane right under the hood forcing the hot air out to the windshield end of the hood. Im not really sure if its worth doing, or if it will actually work.

[owequitit]

Well like I said, it isn't that big of a deal, and it may help marginally.

I think the previously mentioned mods, would help more, but that is just an opinion based on experience.

On B18 swapped Civics with HASport mounts, it is necessary to "vent" the hood to get the hood to clear the valve cover. I think at some point it became sort of a fashion thing too.

And no offense towards you or anything, but Super Street isn't exactly the finite source of aerodynamic information...because there are almost 0 body kits that do something positive from a functional standpoint. They have typically been bigger into the "fashion" of the automotive scene.

Read the Sport Compact Car article in the mag with half of an orange 350Z on the cover. It is interesting to see how many of the different "mods" actually help the car go faster or perform better.... Not the result you would expect.

You can probably see it on the website if you can't find a hard copy.

The fact of the matter is, that modding cars is great fun, but it is very hard to beat the OEM's without losing

1)comfort

2) reliability

3)drivability

or some combination of the 3

They spend billions of dollars on solutions to problems you or I haven't even thought about, and they have the resources to verify EVERYTHING. There is room for improvement on all cars (especially on an individual basis, because everybody prioritizes differently) with much success, because of the compromising nature of designing a car. But much of what you will hear, or read or see, may not make much of a difference at all.

I have experienced far larger gains with OEM Honda parts from other cars, than I ever did with the expensive aftermarket hype that I bought. It was much cheaper too.

Based on your post, I am assuming you are looking for a mild gain without a lot of trouble. Since decreasing intake temp will give you about a 1% HP gain for every 3 degrees you drop it, the previously mentioned stuff will probably still give a better gain.

With a cold air, the outside air will be traveling through the system fast enough to gain little if any, temp based on just the airflow. Then if we can prevent heat soak in the intake manifold, we can keep the intake charge cooler all the way to the combustion chamber, which is where it counts. This is where the phenolic intake manifold gasket comes in. They are proven time and again to drop temps by up to 30 degrees and sometimes result in as much as 10WHP on the higher side. Typical results seem to be about 5 whp.

Since the exhaust system is a major source of heat in the engine bay (exhaust gas is about 1500 degrees F), the header wrap alone will drop the overall temp significantly, again resulting in less heat soak.

Ultimately, if it is what you like, then go for it. If it is for aesthetic reasons, fine, just understand what the trade offs are for what you are doing, before you do it.

I am not saying don't do it, either.

You will avoid a lot of life's potential pitfalls that way.

[92DX]

Damn, you seem to know alot, props . I guess im gonna with heat wrapping the headers.

[owequitit]

Damn, you seem to know alot, props . I guess im gonna with heat wrapping the headers.

I love aerodynamics, and have been around for awhile.

I was also going to tell you, that there is an article in the new Sport Compact Car (The F & F 3 issue) about vehicle aerodynamics. It is very basic, but technical enough to be very informative too.

[asleepz]

I've heard using that header wrap can cause your header to crack...

Forgot how it did it, but there were a few stories.