patman

iTrader: (3)

hey all

i am thinking about a ram air intake system using a hood scoop. basically, i am wondering whether it is better to put a forward facing scoop at the front of the hood or a backwards facing one at the back.

anybody know about aerodynamics?

supposedly (according to a higher level aerospace engineering student..im a freshman) the rear facing scoop at the back of the hood creates a vacuum effect.

is this true, and if so will it force in more air than what would be shoved in at the front at say..100 mph?

thanks

Pat

1987RX7guy

iTrader: (3)

Search for a thread I had about ram air when I was making my intake. Basicaly it is useless untill you get up to around 80-100 mph. I would say get a foward facing hood scoop around the stock location the box is at and a bit poped up if you really want to try this. Then make it so the filter sticks to the top of the inside and seal it off. That way the pressure will be forced into the filter and not just the engine bay.

88IntegraLS

Ram air off the hood via a front facing duct opening is not feasible in my opinion, unless you were wanting something huge which looked like the inlet for a giant supercharger.

An inlet at the union between the hood and windshield would be semi-effective (notice the fresh air vent grille for the climate control system, and how air rushes in through the grilles when you put your logicon to 'fresh'). Still, no ram effect takes place there.

The best position is where all the factory inlet grilles are: on the front bumper below the rub strip. The FC spent time in the wind tunnel before it was mass produced, so I trust Mazda's engineers with their choice of this location for the radiator and brake duct inlets.

patman

iTrader: (3)

yes but i dont wanna steal any air from my radiator as i have trouble keeping my car cool already. might hack up a bumper cover and try something like right in the front like where the trim strip is...

oh yeah and my idea was a rectangualr scoop adapted to 8" round air hose which will fit nicely around my cone filter...and seal it all off of course..and heat tape it.

thanks for the replies guys

pat

1987RX7guy

iTrader: (3)

If your having cooling problems stop doing performance mods and fix the car man. You should have NO problems if everything is tip top.

BTW check out our intake setup. My car has yet to even get WARM with the filter in the NEW position infront of the radiator.

patman

iTrader: (3)

yeah well..i need a better radiator..stock rad jsut cant support my hp that im making now..but..i wanna do this first..im not having real bad problems..just gets hot in traffic and at extended high rpm runs.

its not a problem yet, but if i put a bunch of **** in the way of my cooling airflow...

and yes i have looked at your..and other..cold air system.
however, i believe that if done right, i can get a signifigant increase in my intake charge and possible even make 1-5 psi from a ram air system.

1987RX7guy

iTrader: (3)

You will not get that much. Search for that thread. They posted up a link. The article said you could barely brake .01 PSI or something like that.

Black13B

iTrader: (1)

OK, say it (somehow) does make this amount of pressure.

Are you going to have the fuel mods and ECU mods to back it up? Is the ECU going to know what's going on? Likely not with an AFM.

Also, with the stock N/A UIM and LIM, that "Rammed" air isn't going to go anywhere, IMO. Follow the runners. For it to have any (decent) effect, you are going to have to modify the whole intake from the LIM up.

It's better to use the hood scoop idea as a means of TRUE fresh air intake. What better air is there to breathe than the cool wind outside the car?

dr0x

Too lazy to read this crap. But for an effective one, look at how the STi hood scoop is designed. Btw do those come with warning signs for low flying aircraft?

patman

iTrader: (3)

yes i have the mods..yes the na intake is restrictive...but..NAs do have a pressure sensor and it is there for a reason..the ecu is able to adjust for up to 2 psi? i think..

and hey... lets say that i do make 2 psi at the afm...so maybe it does get wasted in the intake manifolds...is my car gonna be any slower? no. is it gonna be any faster..yes. maybe not much..but a little bit faster and more efficeint means a lot to me especially with something like this that is my idea and inexpensive.

so..i am still gonna do something along these lines..probably the front and center bumper mount rather than hacking a hole in my hood. i have been thinking about a bigger air inlet in my bumper anyway, and that allows for a straighter path to the intake manifold, too.

thanks for all your advice (and if you have more, lets hear it)

-Pat

Black13B

iTrader: (1)

If you really want a good "Ram Air" setup, there is alot of things that have to be done for it to actually work. Otherwise it's just going to be sucking in the fresh air.

patman

iTrader: (3)

ok..like what?

Black13B

iTrader: (1)

Custom designed or modified LIM, UIM, TB, (No AFM), Air filter setup.

You could do it with stock parts, but it wouldnt be worth calling a "ram air" setup. It just wouldn't be efficient enough.

patman

iTrader: (3)

well i do in fact have a ported and polished intake system. as far as i cna tell, the bottleneck is my afm...which (correct me if i am wrong) is impossible to remove or fix without a standalone, which is much more money than i have.

so...the upshot here is that if i can get lots more air past my afm..then i can geta signifigant..or at least noticeable.. power increase. a scoop seems like it would have no problem doing that.

skyypilot

Ram Air works great if done correctly. And 3 psi is very possible. Source the air at a high pressure area of the car, such as the leading edge of the front bumper. I wrote a long post on this a long time ago, I don't have time to search for it buy maybe you do. ~Sky

patman

iTrader: (3)

yay finally some positive feedback!!
thanx sky.

not that everyone elses isnt helpful as well...

Black13B

iTrader: (1)

I wasn't being negative. Just saying it's alot more work than you think to achieve what you want.

Truth hurts.

Rex4Life

You won't get a huge amount of inlet pressure using a scoop. The max you could get is whatever the dynamic pressure (qbar) is for a given speed and altitude. Since you're in AE go ahead and figure it out, qbar = 1/2 * density * velocity^2 . I can tell you it's not much @100mph/sea level.

Most of the hood scoops you see are for turbo intercoolers where heat transfer is the desired effect, not ram pressure.

Anyway, good luck.

projekt

placing the filter (or initial ducting) where the stock box gets its feed from, above the radiator, will not 'take away' air from your radiator. you see a radiator is like a cheese grater. go run water full stream over a grater in your sink. i'll give you a cookie if every drop makes it through the holes.

BLUE TII

iTrader: (9)

I would prefer the design of a rear facing vent as close to the windshield as possible.

This is a high pressure air zone on the car as opposed to low pressure anywhere else on the hood.

There should also should be less aerodynamic impact (if both scoop locations were equally engineered).

Your point about figuring when pressure under the hood is going to be higher than above the hood is an excellant one.
In order for either location to work the scoop must be sealed to the intake.

Anyone that has their hood EXPLODE upward to the safety catch @ over 100mph (I think my incident was 140plus from memory) knows there is a HELL of a lot more pressure under the hood than above.

patman

iTrader: (3)

ok i was not referring to putting it where the stock intake goes, but rather in the 'mouth' area. where it would block air. take your cheese grater, put it in the sink, then put a spoon on top of it. is there a dry spot? you bet your ***.

next point..with the hood closed, there is not more pressure under it. it is only when air is able to come in under the front edge that this happens.

my current idea is wavering between a rear facing scoop in the very back and a scoop right at the front of the hood. like if i were to cut the top 2 inches of bumper cover and the front 4 of the hood and put a nice wide scoop right there.

byt he way, i saw a pontiac grand am or some damn thing today with stock ram air and was checking it out..looks a lot like that second idea.

oh and one more thing:
GIMME MY DAMN COOKIE!!!!

pat

patman

iTrader: (3)

what are the units for that equation rex4life?
cause i hope i did it wrong:
.002738 slug/ft^2 *(146.6 ft/s)^2 * (1/2)=29.42 lb/ft^2

or .204 psi
dammit...

ok but wait...if pressure is inversely proportional to volume..and i have a afm that is 2" by 2.5" ...
and a scoop that is 3" by 18"...and the pressure at the scoop is .204 psi...then would the pressure at the afm not be 2.2032 psi?

so..in less than ideal conditions..i could get maybe 1.5 psi...which could make about 10 hp....

tell me if i am very wrong here.....

pat

patman

iTrader: (3)

patience is a virtue..but who said i was virtuous?

bump

88IntegraLS

This thread just screams for a real engineer to lay down the mathematics behind calculating air pressure for a given temperature, pressure, velocity, and coefficient of drag.

A simple equation, not considering the slight effects of temperature and barometric pressure changes, could be P=KV^2, where P = pressure on whatever object is being pushed through the air, K = its coefficient of drag, and V = velocity.

Getting the units correct is the hard part. I'm working on it . .

Evil Aviator

You guys are killing me here.

Search the internet for the "dynamic pressure" equation, and you will find several forms of the equation.

However, you can just forget all that and read here for a less technical explanation. It's not exactly correct, but close enough for the purposes of this subject.
http://www.viperclub.org/faq/naca.html

It depends where the scoop is on the hood, and how the scoop is designed. These pictures may help:
http://www.geocities.com/mcgumrapper/aerodynamics

Maybe the same, I'm not sure. Try it and find out.