venting engine bay

[Mr.s13r]

Do you guys do this?
Technical Articles: Increasing Engine Bay Venting

Is it really that beneficial like the thread poster said? What are the cons to this?

thanks

[Matej]

Originally Posted by Mr.s13r

What are the cons to this?

It looks ugly.

[slider2828]

I do.... SRs run kinda hot.... I vent it cause of the turbo timer and stuff....

[S14DB]

It only works standing still. At speed it increases under hood pressure. Possibly reducing flow over the radiator.

[!Zar!]

Originally Posted by S14DB

It only works standing still.

Ding ding ding.


In other news.

Why does it say, "install" takes an hr?

They got to be kidding.

[Sileighty_85]

Its the poor mans hood vent

just buy a vented hood not to expensive from here
CW Flared Hood | S13 [H234] - $299.00 : Chaser Aerodynamics, LLC

I bought mine from these guys, products not bad but their shipping methood sucks

[!Zar!]

Or just make a vented hood out of an oem one.

[slider2828]

It would not reduce radiator flow if you have a top panel, but if that at speeds... Yup hence turbo timer...

[MetricHotrods.com]

food for thought.

someone on the british GTR forum got scientific about hood venting. basically they came to the conclusion that any hood venting takes heat from down low (downpipe ect) and pulls it up high, past your intake manifold and intake. heat that, if your hood was standard, would get sucked out underneath your car. the guy hooked up a couple temp sensors and everything.

[tckracker]

I would say just don't rearend anyone because that hood WILL shear those bolts because of the the increased moment force and come visit your face in the interior. I would try not to disable safety in my car. Just my .02
-Shaun

[racepar1]

That is NOT the way to vent an engine bay, The area at the bottom of the front windshield is a high pressure area. By lifting the back of the hood like that you are letting more air into the engine bay from the back. That by itself may be ebneficial, but more air in the engine bay means more pressure in the engine bay. That reduces flow across the radiator, which is very, very bad. To properly vent an engine bay you want to increase the airflow through the engine bay, which means to reduce the pressure inside the engine bay. Lifting the back of the hood does exactly the opposite of what you want. The above principals are the reasons why cowl induction hoods were so popular and effective. Look at nascars, they have cowl induction because the pressure at the bottom of the windshield has a ram air effect. The LAST thing you want is to ram air into your engine bay from the back.

[racepar1]

Originally Posted by MetricHotrods.com

food for thought.

someone on the british GTR forum got scientific about hood venting. basically they came to the conclusion that any hood venting takes heat from down low (downpipe ect) and pulls it up high, past your intake manifold and intake. heat that, if your hood was standard, would get sucked out underneath your car. the guy hooked up a couple temp sensors and everything.

Heat rises dude, the top of the engine bay will always be hotter than the bottom. The people on that GTR forum are retards.

[trsilvias13]

only other benefit is for hood clearance where some motor or part of it sticks up

[zaquanh]

super old topic , search

juss get an actual vented hood

[MetricHotrods.com]

Originally Posted by racepar1

Heat rises dude, the top of the engine bay will always be hotter than the bottom. The people on that GTR forum are retards.

heat doesnt rise when a car is doing highway speeds and its being sucked out from underneath.

[irax]

Originally Posted by Mr.s13r

Do you guys do this?
Technical Articles: Increasing Engine Bay Venting

Is it really that beneficial like the thread poster said? What are the cons to this?

thanks

i've done this with my s13 and I noticed a difference in all around temps, especially driving at night. 2 inch is way to crazy, honestly 7/8 of an inch was enough to make a difference.

[projectRDM]

Holy fuck, is it 1967 all over again? Hot rod guys did this shit even before fuel injection was mainstream.

[MetricHotrods.com]

rdm, its been established that everything in the import scene is just something an aircooled VW person did 30 yrs ago. big deal. stance, camber, offset, fender flares, wiretucks, paint, engine swap ect ect ect...

[racepar1]

Originally Posted by MetricHotrods.com

heat doesnt rise when a car is doing highway speeds and its being sucked out from underneath.

Heat still gets trapped at the top of the engine bay as there is very little airflow up there. I would LOVE to see some actual proof that the air is being actively sucked out of the engine bay as well.

[S14DB]

Originally Posted by racepar1

Heat still gets trapped at the top of the engine bay as there is very little airflow up there. I would LOVE to see some actual proof that the air is being actively sucked out of the engine bay as well.

There is negative pressure under the car that sucks the air down out of the engine bay. Why the stock areo tray is designed like it is.

There is positive pressure in front of the windshield. When you jack up the hood in the rear it lets that air into the engine bay. Staling out the air that was being sucked though the radiator. Easier to go from an open high pressure area then though a screen.

The Hoods with vents work cause they are before the bubble in front of the windshield and use the suction of the air flowing over the hood to suck air out.


Muscle cars from have the cowl induction hood to use the high pressure to ram air into the intake. Not for cooling or venting.

[racepar1]

Originally Posted by S14DB

There is negative pressure under the car that sucks the air down out of the engine bay. Why the stock areo tray is designed like it is.

Yes, but at the top of the engine bay there is very little airflow because there is no way out up there. That is the hottest part of the engine bay. I still don't think the pressure differential is enough to actually be considered actively sucking air out. And I am sure you know this, but the pressure under the car is not negative, just lower than the air on the top.

There is positive pressure in front of the windshield. When you jack up the hood in the rear it lets that air into the engine bay. Staling out the air that was being sucked though the radiator. Easier to go from an open high pressure area then though a screen.

Yes, that is exactly what I said in my OP.

The Hoods with vents work cause they are before the bubble in front of the windshield and use the suction of the air flowing over the hood to suck air out.

Yes again.

Muscle cars from have the cowl induction hood to use the high pressure to ram air into the intake. Not for cooling or venting.

I never said it was for cooling, I said it had a "ram air" effect. Maybe this was not directed towards me, but since my post was quoted I figured I would respond.

[S14DB]

Originally Posted by racepar1

Yes, but at the top of the engine bay there is very little airflow because there is no way out up there. That is the hottest part of the engine bay. I still don't think the pressure differential is enough to actually be considered actively sucking air out. And I am sure you know this, but the pressure under the car is not negative, just lower than the air on the top.



Yes, that is exactly what I said in my OP.



Yes again.



I never said it was for cooling, I said it had a "ram air" effect. Maybe this was not directed towards me, but since my post was quoted I figured I would respond.

Originally Posted by racepar1

Heat rises dude, the top of the engine bay will always be hotter than the bottom. The people on that GTR forum are retards.

The GTR forum is right. The air goes though the radiator. The swirls in the engine bay and is sucked out the bottom by the venturi effect of the air rushing under the car.

The air coming in the top negates the venturi effect and stalls out the air from swirling in the bay.

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[racepar1]

Originally Posted by S14DB

The GTR forum is right. The air goes though the radiator. The swirls in the engine bay and is sucked out the bottom by the venturi effect of the air rushing under the car.

The air coming in the top negates the venturi effect and stalls out the air from swirling in the bay.

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Yes, but the top of the engine bay is still the hottest part of the engine bay because the air stalls out there due to all the crap in the way (engine and shit). That is why a properly vented hood lowers underhood temp and pressure. It is not better for cooling to have a non-vented hood, which is exactly what the post says. That shit is wrong and so is the GTR forum. It has been PROVEN that a PROPERLY vented hood lowers underhood temps, even at speed.

The stupid ricer hood spacers are just that, STUPID. NOBODY is is arguing that point, I don't know why you continue to argue it.

[corey240]

Well gentlman put your penises away. Your both arguing the same point. Question: If I make a metal/composite undertray, up to the back edge of the front bumper, would it assist or hurt the air sucking effect under the car? I mean is there a way to, assist the air flow down. I plan on going with a vented hood, one wit the 5 vents in the middle, "drift" hood lol. And I want an under tray since mine fell off. So would it make a difference? Its for protection only but I wonder.

[Mr.s13r]

Wow damn all of these are very informative well then i'll not go with the spacers but then what you guys think about this but for the 180sx:

http://us.st12.yimg.com/us.st.yimg.c..._2030_52139516

[g6civcx]

I'll try to flashback to my motorsports engineering classes from 15 years go.

I realised from the beginning that aero is pretty much pure speculation. You either have to rent a full scale wind tunnel to the tune of $10k per hour, rent a smaller wind tunnel and build a scale model, or at least do computer simulation.

Everything else is pure speculation. That's why I stuck with digital control systems.


Trying to move air molecules is like trying to herd a group of very antisocial and lazy people. When you group them together, they try to spread apart as much as possible via the path of least resistance.

Air will try to move from areas of crowding (high pressure) to areas with open space (low pressure).


When a car is traveling through air, the highest areas of pressure are 1) the leading edge of the bumper, and 2) the base of the windshield.

Any time you try to separate air layers and puch a hole through the air you will get resitance.

Airplanes try to make the fuselage as pointed as possible to reduce drag. Also, "sports" cars have steeply raked windshields to reduce drag as well.


Generally, in order for air to move through the radiator fins, you need to create an incentive by putting a low pressure area directly behind the radiator. You can do this with a fan, and/or by blocking all other paths of travel with cooling panels.

Once air is in the engine bay, it needs to leave. You can use undertrays to create a venturi effect and force the air to travel between the engine and the undertray. This can also create front end lift as the air travelling below the car lifts the front end.


The other area is the base of the windshield. If you cracked the hood open, the area under the hood near the valve cover would have low pressure. The air would go from the high pressure area of the base of the windshield into the valve cover area. Then where would it go?

If you have your intake where the valve cover area is, which is where Chevy small blocks do, you can take advantage of the ram air effect and suck in more air into the carb. Otherwise air would stall around the underhood area and run into each other.


Again, these are just generalizations, and it depends on the specific design of the car. Nobody is right and nobody is wrong. It's just opinions.