Vented hoods...

[Groomz]

Check this one out, Wobble:

 

[kpt4321]

Originally posted by crankbender
I just want to point out that the vents are facing backwards not forwards on the good ones . If you want it to look like a ram air you have the wrong idea....it should kinda look like a scoop facing the wrong way for best results. Also placing them just in front of the strut towers is a good place as it clears 75% of the engine bay and doesn't inpeede into the high pressure area at the beginning of the windshield. Yes this will increase the temps of the air going over the crew cap.

The cars are able to get plenty of air in typically they can't get it out.

Yeah, right on. I probably should have specificed.

The scoop types are generally not necessary; as you said, in most cases, there is no problem getting air in, just getting it back out.

Certain cars like WRX's need the scoop because they have the top mounted intercooler. Otherwise, it's not worth the extra aero drag, and all the water you will get in the engine bay.

In a lot of cases, I personally would use the vent between the manifold and the radiator. Depending on what you are trying to achieve, I think that the best location may differ. If you're solely looking for flow through the radiator, put the vent right behind it. If you want to cool down the engine bay in general, then put it by the rear of the hood.

I'm probably going to be changing hoods and buying vents this upcoming season, and I still haven't been able to decide what I am going to run. I'm definately going to run a vent post-radiator, but I don't think I will stop there. I'm tempted to run either a NACA duct in front of the filter, or maybe run a vent behind it. On the other hand, maybe I will toss the filter into the fenderwell and be done with it.

In that scenario, a second vent as the rear of the hood may be a good idea.

 

[greyforestgst]

Originally posted by Wobble
Well, i guess im gonna try and do vents on my own hood, I cant seem to find a CF hood that i like really so i guess this is my best idea.. I just want the holes bigger than the ones already posted though.. trying to figure out how.. im sure partially cutting into the "bracing" underhood wont cause any probs and i have the tools to do it available.. just trying to think of the best shape for the holes.. will prolly just do a shape simplar to the one posted, only bigger..

you could always just cut through the middle of the two vents and make it one big one. if thats not enough, there is another pair of symmetrical flat parts behind the first pair i used; you can partially go in to those with no problem and not even get to the start of the tbelt bump.

i did mine that way because the shapes between those ribs were in a good location and were a neat shape. cutting through the ribs won't hurt much, if anything. i think SCC cut all the ribs out from under the hood of one of their budget race cars, and all it did was vibrate annoyingly at high speeds. hood pins are cheap.

 

[kpt4321]

Originally posted by Groomz
Check this one out, Wobble: (picture above)

I don't like that hood as an example.

First of all, if you run bigass vents like that above the valve cover, your spark plugs and wires are not going to be very happy (especially once the valve cover becomes a swimming pool overnight. )

Second of all, you need to understand that the vents will be MUCH more effective if there is a lip on the hood before them, or if the lip is integtared as part of the vent. Now, that hood has a lip, so it should work ok in that regard. However, if you were to cut a stock hood and just put vents in it, it will not be as effective.

Thirdly, the location of those NACA ducts shows me that that is certainly not designed from a performance standpoint. There is no reason you need air to cool the strut bolts.

I would use a real performance hood to base your design on.

Something like:

http://www.cse.unsw.edu.au/~awlo582/evo.jpg

http://www.carbontrix.com/images/bigview.JPG

 

[Wobble]

Groomz, whats that hood called, got a link showing it off some more.. specs.. etc?

 

[Groomz]

Originally posted by Wobble
Groomz, whats that hood called, got a link showing it off some more.. specs.. etc?

http://www.i-m-racing.com/visevocafiho1.html

VIS Evo hood. As for a reason to have vents, the car was designed to be able to cool at X horsepower. DSMs are around 210hp. Factory stuff is fine. Running more power? Get an aluminum radiator and some slimline fans. Running 350+whp? Getting really hot down there? Then you'll need to improve the engine bay airflow, which isn't that great to begin with. I like what crankbender said. Some vents near the strut towers are good, as well as a reverse ( scoop mouth towards driver ) scoop on the front of the hood to pull air out or give it a path out ( depends on speed and size of scoop ). Or get the one I linked.

Peace to all,

 

[Groomz]

Originally posted by kpt4321
I don't like that hood as an example.

First of all, if you run bigass vents like that above the valve cover, your spark plugs and wires are not going to be very happy (especially once the valve cover becomes a swimming pool overnight. )

Second of all, you need to understand that the vents will be MUCH more effective if there is a lip on the hood before them, or if the lip is integtared as part of the vent. Now, that hood has a lip, so it should work ok in that regard. However, if you were to cut a stock hood and just put vents in it, it will not be as effective.

Thirdly, the location of those NACA ducts shows me that that is certainly not designed from a performance standpoint. There is no reason you need air to cool the strut bolts.

The VIS hood has a block-off plate to go under the vent, just in case it rains or snows. Its included.

 

[ProjectTwin]

Look at an Evo hood...not the VIS, a real Evo hood. They're vented, you can see right into the engine bay.

 

[ClipseT96]

Do you think this hood would work better http://www.i-m-racing.com/visxtgtcafih.html ? Are these double layerd cf hoods? I know most cf hoods are really cheap and shitty.

 

[DSMJim]

Wow Stop the Press.. You guys are missing the best mod of all for cooling your engine bay! Guess what it's FREE. EASY and Reversable.

My father and I were trying to figure out the same thing. We bought a probe and a digital measuring gauge to test the underhood temps. With the hood down normally it was really hot under there. I don't remember what it was now because it was a while ago, but damn it was hot... So here is what we did.

The bolts that hold the hood on at the back, between the hing and hood we added about a half inch of washers to space the hood off the hinge, we acctually found a nut in the end that spaced it perfectly. You will also need to get bolts about 1/2" longer as well to ensure you have enough threads in the hood to hold it down. What this did was lift the back of the hood up and take it off the rubber seal. We also pulled the rubber seal off the back side of the engine bay to create about a 1" gap. This looked just like cowl induction and really pulled the hot air away from the engine bay.

Just as crankbender said that heat rises, so with the hood propped this is now the highest spot and it's open to allow heat to escape sort of working under the cowl induction thoery. I think it has something to do with creating a low pressure zone behind the opening, maybe he can fill us in better there.

Anyway the 1/2" lift mod is easily done free and reversable. Your hood will only look slightly propped up at the back, nobody will even notice except for you. We tested the air temps under the hood and noticed a huge decrease in under hood temp. With the headlight out for dragracing the decrease was even higher, almost ambiant temps outside. I wish I had the numbers for you guys, my dad would remember but he's not online right now for me to bug. Anyway it was a pretty good discovery.

 

[kpt4321]

Originally posted by DSMJim
This looked just like cowl induction and really pulled the hot air away from the engine bay.

Just as crankbender said that heat rises, so with the hood propped this is now the highest spot and it's open to allow heat to escape sort of working under the cowl induction thoery. I think it has something to do with creating a low pressure zone behind the opening, maybe he can fill us in better there.

Jim, you've got it backwards.

The area at the bottom of the windshield and the back of the hood is a very high pressure area. If you lift the hood like you are saying, then air will ENTER the engine bay back there, and will have to leave elsewhere (most likely under the car).

That's why it's called "cowl induction."

 

[Wobble]

thats wierd.. so you saying at speed the air will actually travel backwards.. going up and under the BACK of the hood INTO the engine bay.. insted of the hot air rising out?

 

[90CherryTSI]

is since there's no "lip" there it sucks the air back down around under the hood? I've seen windtunnel tests and like normal cars I would think technically this would work as the hot air rising out of the back would create enough of a barrier not to let the colder air come in. Maybe since cold air is denser it can force it's way inside and just create a huge pocket of hot air? Although when stopped I'd bet this would work very very well!

 

[Groomz]

If you look at an Evo 8 straight on ( and level with it's headlights ), you will not be able to see the vents in the hood. All you see is the lip before it. This works like kpt4321 said and creates that low pressure zone around the vents to pull all the hot and high pressure air out of the engine bay. The Evo hood for a TEL is angled down slightly, so the gains are not as good. Still, the air enters the radiator, is heated, exits and is faced with either going down or to the sides. With the open vent, it can now go up, and hot air loves to do that. Even a poorly placed vent is better then none at all. Just avoid rice-e-ness.

 

[kpt4321]

Originally posted by Wobble
thats wierd.. so you saying at speed the air will actually travel backwards.. going up and under the BACK of the hood INTO the engine bay.. insted of the hot air rising out?

Well, define backwards.

Yes, it will go under the hood. The base of the windshield is a very high pressure area, higher pressure than the air under the hood. Thus, the air will travel away from the base of the windshield, and under the hood.

Temperature is irrelevant, in this situation we only care about pressure.

 

[coltboostin]

Rx-7 guys have been doing the hood pop trick for years and years, because those damn rotary's love to overheat. It keeps them much cooler, so why would the same trick work for us?

 

[ImportModder]

Like kpt said, it would work for us, just not the way some people are thinking. The propped hood works like a cowl induction. It sucks in the cool air, but the hot air leaves the same way...under the car.

 

[Kingdom]

I would do the trick of raising the rear of the hood if I wanted to autoX or something just for the time being. But it doesnt look good for daily drivers. I want something that functions and looks good too.

Also the new evo 8 hood is the best functioning hood out of all the evos. the Evo 7 and below is just vents with the hood being flat. It does work and very well but still not as good as the 8. Because the air travelling on the hood acts like a shield when traveling fast and the air has to be pushed out of the vent. The new EVO 8 kinda buldges slightly acting like a tiny jump, doing this gives way for the air under the hood to flow out properly out the vent.

 

[Wobble]

I understand the pressure build up on the windshield.. but i fail to see it being STONGER than the pressure of the air coming in the front bumper.

 

[slowboy93]

good advice

 

[project94tsi]

i personally like the vent that the guy had on his black 1g GSX in the sport compact cars ultimate street car challenge. I dont think that him or Roy who also competed in the challenge (silver GSX) would have put hood vents on their car for nothing.

 

[Lowerd1]

Proof is Easy.

Find anybody with functional hood vents on their car after its been driven hard and parked. Now put your hand over the vents, and tell me what temp the air is coming out. Unless its a Stick on vent, the air should be HOT!

My GTP has 2 stock functional hood Vents and I know for a fact they work.

Here is another way to prove it. Open your hood up and start the car and see how long it takes to warm up. Now close the hood and see how long it takes to warm up.

Yet another way. During winter Months alot of people will use Closed front grills on their Trucks to hold the heat in and warm the engine up faster and help to keep it warm while driving trying to keep the cold outside air out and try to not let the engine bay heat out.

Scientific fact that heat RISES.

I would not suggest just cutting a hole in your hood if you plan on driving it as a daily driver. Reason is because you are probably going to drive it during the RAIN in which case Rain will easily get into the engine bay. If you have anyway for it too leak past the Spark plug boot it will, and also if the Filter is exposed in the engine bay then it will soak it. Factory Vented hoods have Drip pans to prevent rain from hitting vital parts. Also there is road debris. I am always finding leaves and all types of crap that comes off the road and somehow gets sucked into my hood vents. Luckily the vents have grills between the vents and the drip pans. I never see it get sucked in there but it never fails I will find atleast one piece of debris after a day of driving. Plus just with it sitting there, I will always get a leaf that falls in there. Nothing major but still kindof annoying.

Good luck

 

[kpt4321]

Originally posted by Wobble
I understand the pressure build up on the windshield.. but i fail to see it being STONGER than the pressure of the air coming in the front bumper.

The pressure of the air at the front bumper is pretty strong. However, by the time it passes through the radiator, slams into the turbo, then the motor, and whatever else is in the way, it's pretty much stagnant.

 

[coltboostin]

Originally posted by project94tsi
i personally like the vent that the guy had on his black 1g GSX in the sport compact cars ultimate street car challenge. I dont think that him or Roy who also competed in the challenge (silver GSX) would have put hood vents on their car for nothing.

Yes, thankyou. This is what I said in page 1, and it is living proof they work. Another thing to consider is that some people w/ carbon fiber hoods and tubular manni's have had problems with the hoods melting under extreme heat.

Can someone explain why the hood pop thing works for RX-7 guys, but it somehow wont work for us?

 

[crankbender]

It does work just not in the way people were thinking. You also have to remember that the side lift off the gaskets too allowing heat to escape out the sides (which are lower pressure areas). As stated before the best way tho is to put the lipped vents on the car. I believe RRE has the covers for sale in their 323 gtx area (if they still have that area.)

http://www.roadraceengineering.com/323desc.htm

about half way down.