I been toying with the idea of installing vents on a spare hood I have that would open up when the motor is in vaccum and close once in boost. does any company out there already have a hood like this for our cars?

 

More vacuum lines WOOHOOO!!!! Hahaha im just messing, but why would you want them closed under boost? Maybe have a switch to close the vents when rain comes.

I do like the idea of putting vents on a stock hood, how hard would that be to do? would stencils and a dremel work?

 

probably would work fine, I figured i'd make the vents with fiberglass so the actuator wouldn't have to be very large. I figured while your at a stoplite the vents would be more of a benefit for heat, plus how cool would it look if every time you shift it looks like your car is taking a deep breath... :p

 

I think it would be more practical to have the vents open and close with the flip of a switch. The only reason you would want them closed is for rain, correct? Truthfully, I don't like the idea of adding more complexity to a car that is already too complex for its own good; but it's your car.

As for cutting vents in your stock hood... you could just dremel out some vents, but they will not perform as well as most of the aftermarket hoods out there since there is nothing to create a low pressure region around the vent. The hot air in the engine bay will tend to stay there instead of being vented out into the atmosphere. To fix this, a lip or small raised edge in front of the vent must be added to disturb the flow.

 

arg, double post

 

I was thinking the vents would pivot up when activated, to help create the lip you refer to

 

The vents should be more effective if you seal the underside of the engine bay, or at least reduce the size of the possible air exits down there. Sealing that area off will require that your hood vents be opened all the time.

If you wanted to get really technical, it would probably help to change the size of the vent to vary the pressure sucking the air out of the engine bay. Accurately calculating the sizes you need will be difficult. All I know about aero stuff is that it's tricky.


Personally, I'd adhere to the KISS theory. (Keep It Simple, Stupid). Actuating systems and hinges will add weight and points of failure, so I would want to be sure that they were really making an improvement.

-s-

 

I have the mazda speed reverse vent hood. I found some closed cell foam pads that are made for filling vented hoods, if raining, etc. I saw them in a JEGS after market brochure. So far when driving or parked in the rain, I have not had any trouble with open reverse vents. Even after washing the car and watching soapy water run right into the engione bay.

 

Damn thats a sweet idea! I wish I would have thought of it. It would be kinda like the 911 rear spoilers that rise up under acceleration. I wonder how much vacuum you would need to make them open up though.

 

Wow...that is a really badass idea. I can only imagine how tight that would be. But it would be so complicated and in order to make it really effective you would need someone with an extensive knowledge of aerodynamics.

 

It sounds like the same thing the old Cuda's used to have. At least I think it was the Cuda's. I think it'd look pretty good.

 

I just don't understand why you would want them closed under boost? Why wouldn't you want them open all the time. You want the most airflow under all conditions, not just while idling. When you are boosting, having more air to flow through the radiator and intercooler will make them cool better.

The only reason to close them, as said before, would be for when it rains, and unless you drive your car in the rain all the time, I don't think it would be worth the time and money to make the system work.

Also, don't cut your own vents in the stock hood. It will most likely look like a low-cost hack job that you would see on a Honda CRX. Just buy an aftermarket hood and make your own flapper door thingys.

 

I've cut vents in a stock hood, it looks really cool ( I'll post pics as soon as I get home) .
I would totally recommend cutting a stock hood simply because you can customize it to your IC /Rad setup and stock hoods are also lighter than carbon fibre ones ( or so I've found ).

 

Several of the old-school muscle cars had cowl-induction hoods (Chevelles come mostly to mind) that used vacuum to keep the vent closed but when you tromped it to WOT and thus lost vacuum the vent would open up to take advantage of the low-pressure area behind the hood/in front of the windshield, this gave you a nice sudden cool intake charge.

On the 3rd gen....I just don't see what you are trying to accomplish? Having some sort of vacuum operated hood vents for....what? Are you trying to improve airflow thru the engine bay? If so, that is something that is good ALL the time. Now, I could see a custom built flapper that opened up directly in front of a stock mount intercooler to allow a large rush of cool air to hit the intercooler as being moderately effective....but beyond that....I just don't see any advantage. Basically you either need to allow cooler air to the intake or to the intercooler. That is where any improvement lies.

 

spekdah, let's see those pics. I bought a spare hood just to cut vents in it.

-s-

 

The next time I'm at Rick's Rotary, I'll take a picture of a track car there that has vents cut into the stock hood. It actually looks pretty damn good and it works.

 

 

Damb...Not bad at all.

 

The vents I just posted probably don't work well because they most likely let air in to the engine bay instead of creating a low pressure area and venting the air out. By adding air in the engine bay you may be hindering the flow of air through the front ducts (radiator and oil coolers).

BTW, that car is from the Getaway in Stockholm video and guess what... it OVERHEATED at the end of the movie.

 

sorry bout the delay,

Here's the stock hood I cut vents into, I used a plasma cutter and as you can see its straight as hell, the cutter does a real good job.

This is my Summer hood to get rid of that excess heat

 

one more.

I must admit I followed the BOMEX style, I like it because from front on the triangular vents facing inwards give the illusion of a wide fat look.
Also you notice that the right vent is blocked with a removable peice of carbon fibre, thats because my filters are right below it and I want as much cool air trapped under there as possible.

cheers
Krisso

 

BTW, remember if ur gonna do this yourself to mark your shapes out clearly and tape ( filament) them for a cleaner cut, this is what the guy at work told me to do but after I'd finished I kinda didnt see the relevance of doing this considering the plasma cutter wont be affected by the tape, but there you go.

 

Got any on-car pics? It looks a bit like the TRD Supra hood. (2000GT?)

-s-

 

I know hood vents does let out the hot air.
Because I can see the heat rising from my vents like a frigin geyser.
But I can't say how beneficial it is when in motion.
I guess it's a good time to hook up a thermometer and see some numbers.
Here is a pic of my small vents I put in.

 

yeah, being winter over here ( new zealand ) its not on at the mo, but I'll chuck it on and take a few pics this weekend.