emilio700

iTrader: (3)

shanem, do you have a reroute?

bbundy

Extreemly wrong vent locations for it to work optimally!!

I have seen guys try to run that vent location high on the front bumper and water being sprayed on their intercooler in the main opening down the front straight would come out the bumper though the upper hole. They had to make a big scoop to get air to go in the hole in the front bumper at that location. CFD pressure maps I have seen for the car indicate that very thing might happen as the area on the bumper just ahead of the front edge of the hood is the lowest pressure region on the front half of the car. Interesting the hole in the top of your hood is in almost the very highest pressure region on the top of the hood.

I am almost positive you will have air entering at the hood opening and exiting out the upper bumper slot.

FWIW- I am a mechanical engineer and spent a number of years doing CFD analysis of air flow in through automotive cooling systems including external and underhood flow.

Bob

dgmorr

iTrader: (4)

Off topic, but what turn did this happen on?

SmokeSR

iTrader: (1)

Turn 1

dgmorr

iTrader: (4)

Damn, not that ay turn is less worse, but that's a scary turn for an incident like that to happen.

EDIT: Oh just saw this

SmokeSR

iTrader: (1)

Oh, guess he ended up at corner 1 cuz that's where he was.

I'm not worried and still running my 9's. Those are 2 year old 15x8's on a 350hp/250tq Civic on NT-01's. The metal did look porous inside though. I know Emilio has made a few strength changes between generations as well.

Double O 86

Here go one: Garage Vary Bonnet

I'm going out on a limb and say that this one has the vent placed properly.
Discuss.

9671111

iTrader: (10)

You're really explaining this to the wrong people lol.

shanem

iTrader: (1)

i don't know anything about wrong or right vent locations. All I know is there are three of these cars at MSR Cresson, built by the same guy, two of which have been in service over 7 years of beating on them in the texas heat year round, one is even a rental for HPDE days, the other is driven by Keith verges. and they haven't had over heat issues. Granted the cars have lots of other cooling. i figure if Keith cant over heat the car, i should be fine. Unless its his sheer speed that keeps the car cool from the mass of air running through that opening.

I'm trying to recall what it looked like back behind that bumper opening. i don't have the car home yet, it's getting the final set up. I want to say that there is some sort of aluminum duct behind that bumper opening that forces the air to the radiator. you can see a bit of something in the opening on that pic.

i am curious though, what would be a more appropriate location? lower down or just have a scoop of some sort like you mention.

emilio, im too new to the miata world to know if it has that or not. it's not on the parts list, so i'd assume no.

slmhofy

iTrader: (5)

That one does actually look pretty good.

rleete

iTrader: (21)

Lower down. Like at the start of the hood bulge. Actually, just a couple inches further back, but it's hard to get a duct into the opening to sit flush if you cut the bulge.

bbundy

Look up Bernoulli Principal for better understanding.
High relative velocity = Low pressure
Low relative velocity = High pressure.

As the car travels through the air the air stacks up compresses on the front of the car making it low relative velocity to the car on the forward facing surfaces of the nose of the car and high pressure. The air has to force its way around the car however the compressed air on the front nose accelerates rapidly as it transitions from flowing next to Vertical facing surfaces to flowing next to longitudinal facing surfaces it is also expanding generating very low pressures at the transition area around the perimeter of the bumper. The air gets slows down and compressed again at the base of the wind shield where the surface orientation transitions from longitudinal to more vertical again and the base of the wind shield and out part way on the hood is higher pressure again.

Significantly higher pressure on the aft part of the hood than where the surface transitions from vertical to longitudinal around the perimeter of the nose of the car. From evedence I have witnessed a scoop is required at that high location on the nose to make it behave more like a forward facing opening than just a hole in the surface the air is shooting across to get around the car. The engine compartment is fairly high pressure because it is fed by really good high pressure on the nose of the car through the main opening in the front bumper.

Best place to vent the hood is as far forward as reasonably possible on the hood likely just aft of the radiator.

Bob

jmann

Looks like I got a good discussion started. I think the fault in your friends hood design is the location of the top rear vent. It is in a fairly high pres. zone on the hood. It still may have some effect if the intake on the nose is ducted up tight to the rad. as it then may have more pres. from the insde at its location then is being created from the outside pres at that location, but moving the air outlet forward would create alot less high pres and thus even better evacuation of the incoming air from both the grille and the nose and thus better cooling and less high pressure in the engine compartment. This is assuming that he has a duct in there tight to the rad.. If not as Bob stated the air coming in the grille well most likely just go out the nose opening as that well be the path of least resistance, low pres. area verses higher pres. area on the rear top of the hood. Also it sounds like Bob thinks the nose area may be lower pres. then the aft hood location vent, thus even with ducting to the rad., it's effectivness may be greatly deminished. Just my 2 cents.

jmann

Well I just received the carbon hood from Chasers and I must say I am impressed with the hood and the boxing of it. First off Dgmorr is right in the statement that the gaps are a little wider then stock, the sides are not bad, but the front gap is a lttle large if you are using it for a street car and want a little tighter gaps. The front one is 5/16" and both the sides are 1/4" rear going to 5/16" as they come forward. To be honest the sides aren't alot more then the stock one was and no worse then I've seen on some other stock miatas. The gaps are pretty consistent so it actually doesn't look to bad. The contours on both sides match the fenders right on and the shape across the hood is very good, follows the contour of the front nose exactly. Considering what I've seen on hemi hoods of yester year and fiberglass and carbon fiber pieces on other miatas and other cars with carbon fiber parts, it fits especially fine, especially considering the money people paid for some of the other products. I well probably take a die grinder and enlarge the holes in the hinges forward about an 1/8" where the hood mounts, no big deal.
It came very well packed as it took me 15 mins to cut it out of all the bubble wrap and reiforcement pieces on the edges and rear corners and it was packed in a very heavy cardboard box with all kinds of warning labels stating not to sign for it until you have inspected it, with a warning to the trucking co. that this is a expensive claim item.
It is exactly what I want for the track car and well function exceptionally well for my purposes of greatly increasing the air flow through the rad. and out of the engine bay as well as relieving under hood pres as the very large louvers are in the perfect location. I would highly recommend it especially for a force inducted NB car being heavely used on the track. I well try to get some pics posted later.
As for weight, the hood with the rain gaurds removed, weighs 1/2 pound more then the stock hood and the rain gaurds weighed 2#2 oz for the pair, so the hood weighs 2#8oz.'s more then a stock one with the rain guards installed, which they won't be on this car. The finish is very high quality and shine, all one would have to do is clear coat it to keep it from yellowing if being used on a car that is outside alot.

Handy Man

Some visual representations of what you guys are trying to explain:

shanem

iTrader: (1)

so the green would be low speed airflow and the red high speed, or is that pressure? i wonder if the design of the 94 woudl have different flow?

jmann

Shanem The arrows pointing towards the body are high pres areas [air trying to get in to the body] and the arrows pointing outward are low pres areas, they are the areas that if you open with say a vent well more easily release internal air presures and allow the air to flow out ,as the internal pres has a greater chance of being greater then the external pres, and air like water well always seek the path of least resistance. The longer the arrows the greater the low pres. area is, hope that makes sense. Thanks Handyman

shanem

iTrader: (1)

cool, tks

bbundy

The upper plot appears to be a cross section plot of total pressure. I dislike looking at total pressue because it is hard for me to visualize what behavior will result. It is a combination of static pressure and dynamic pressure so it has a normalized velocity squared term in it. You don’t know for sure if the color of an area is mostly the result of static pressure or velocity.

The second plot is very useful It is a plot of static pressure at and normal to the surface of the car. And it would represent the direction flow would go if you put holes in the surface and if the pressure inside was held at ambiant. Note the upper portion of the bumper with the upward facing surface orintation to it is an extremely bad place to put an inlet. Also note the aft portion of the hood is not good of place to put an outlet. The picture is not a Miata but the plot would look very similar.

Bob

Doppelgänger

iTrader: (12)

I like this thread...and it all seems pretty logical and easy to understand. A lot of what Bob is talking about are things I've picked up on over the years of talking/reading.