That's exactly what I'm envisioning! I look forward to seeing your images, and maybe a parts list????

 

some pics

 

thanks I was anxiously awaiting. Any with hood up and detail on the cut?

 

got it all done at my bodyshop...so dont know about the cut etc...

 

thats pretty crazy man. let us know how it all works out perfomance wise.

 

so it's just a funnel in to the engine bay?

 

Well i havent done a before and after dyno....but i know it can only help matters (in terms of power)....it has been strategically placed to give a direct flow of cold air to the Air filter of my single turbo.......so no hot air for me!!!!

 

Thanks for the pics. your hood looks pretty good. do you have a pfc or something to monitor air intake temp? what are your hottest intake temps if you sit in traffic on the hottest days? Did you notice if your temps were cooler? I see you have a front mount IC. please post a pic of your air filter area under your hood, and go ahead show off other engine pics.

 

Yes i have a pfc.......air intake temps...in traffic are around 40-45c....but this nothing to do with my bonnet duct...as this only comes into play once moving.....as its sole purpose is to feed cooler air to the turbo/filter when on the move under boost.

 

right, but even when you're sitting still your engine is ingesting air, not as much, but air none-the-less.

any way you could do a vs test for us?

Cap off your duct drive around for 10 miles or so then do a redline pull. log temps.
uncap your duct drive around for 10 miles or so (same place, speed, etc.) then do a redline pull (same gear, same place, etc). log temps.

 

doesn't air at idle come through the filters on the primary turbo?

Is the 40-45 the highest you've seen? If you think about it, this summer post some numbers. I'm still interested in pics of your intakes and motor.

I use to have a spitfire, it had a bonnet.

 

If anyone is thinking of doing this to a track driven car, pretty much anywhere on the hood is a bad idea for a NACA duct to bring in air. If you are only using it to bring cool air into the engine bay or evacuate heat, that's ok, but not if you are going to duct air directly to a sealed turbo inlet. Actually, it's ok to about 100 mph, after that's it's not a good idea. Does look cool though.

 

Can you explain why it is a bad idea, please?

 

you could make a vent in the bumper also, which would be less noticeable than putting holes in the bonnet, like this

 

i have a single.

 

yes do tell....as RE do a similar thing with their headlight duct...and i'm pretty sure they see over 100mph on their cars.

 

sorry bud..i dont have time to do this at the moment.....when i do i'll let you know.

 

NACA ducts are primarily for use in areas of low pressure or a very thin boundry layer of air. At higher speeds, the air stream over the nose of an FD (and most cars) arcs up over the hood enough to cause a vacuum in most places on the hood. Once there is a vacuum, there is no air available to enter the duct. In fact, the under hood pressure caused by air entering the nose creates such a high pressure differential between the topside and bottomside of the hood that air will start to exit the duct instead of enter. This is why NACA ducts or any reverse duct works great for evacuating heat from under the hood. I actually tried running 2 NACA ducts on my hood when i still had stock twins with 3" hoses directly feeding the turbo inlets. After about 95 mph, the boost would drop to about 5 pounds or less and fluctuate a lot. At this speed, there was no air available at the surface of the hood for the turbo to suck in. At low speeds, the duct "could" work, but given the high underhood pressure caused by most aftermarket bumpers, it's doubtful it's doing it's job.

 

The design of a NACA duct is primarily to allow an intake of airflow without disturbing the laminar boundary layer airflow and thus create drag. Nearly all conventional intake ducts create drag to some degree.
The airflow going up over the hood doesn't create a "vacuum with no air available". The longer distance the airflow has to travel over the hood in relation to the airflow going under the car means that airflow speed over the hood is increased, thus pressure is reduced above the hood surface compared to the pressure underneath the car (Bernoulli's Principle).
The air entering through the radiator intake doesn't create pressure in the engine bay; air pressure wants to equalize, so it will go to wherever the pressure is lower (above the hood in certain areas). The only area where pressure is actually created (higher) is directly in front of areas where airflow speed stalls and backs up, causing spillover (like directly in front of the nose, the windshield area, etc.).

 

thanks for including your experience. so you were trying to use ram air with the naca ducts and you were losing boost at 95 mph. were you running open filter? I know I lose boost at some point around that speed, I'm running 2 k&N's near the radiator. I think if I get the turbo's to spool, I hold onto boost through that speed, but at that point focus on the road becomes a priority. I have no idea what my boost is at top speed. I take it you can hold boost over 10 psi over 130 mph?

 

[QUOTE=Synaptic 3;7880994]NACA ducts are primarily for use in areas of low pressure or a very thin boundry layer of air. At higher speeds, the air stream over the nose of an FD (and most cars) arcs up over the hood enough to cause a vacuum in most places on the hood. Once there is a vacuum, there is no air available to enter the duct. In fact, the under hood pressure caused by air entering the nose creates such a high pressure differential between the topside and bottomside of the hood that air will start to exit the duct instead of enter.

Interesting...... Try taping some yarn/tread/strips of paper in front of the duct and see if this is true. I thought at those speeds air would be forced in any openings in front of the car

 

That's not the main reason you were encountering problems at high speed. The reason is because you had a high speed airflow directly over your inlet, which causes extreme turbulence right at the entrance, resulting in less actual intake volume and drastic fluctuations in intake airflow. This is the reason why dragracers soon discovered why they had problems at higher speeds with the velocity stacks sticking out in the open, so they covered them with a cowl to stop the airflow over the stacks causing turbulence. No matter how much your turbos were trying to draw in air, the turbulence was substantially reducing that ability. Because a NACA duct disturbs the airflow as little as possible, the airflow speed over your inlets was substantial.

 

does anyone know where I can purchase NACA style ducts/vents? I need the actual vent NOT the tube style (brake duct).

Thanks,
Dan

 

http://www.mckinneycorp.com/

You have to scroll down using the site's scroll bar, your browser scroll won't work...

 

Thanks!!

I'm wondering if I should use a few of those for my undertray (v-mount outlet air) or a few louvers. I can't find any decent priced louvers either.