Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gldndrgn14 &raquo;</TD></TR><TR><TD CLASS="quote">i couldnt understand his engrish until i read your post. haha but on that topic, dont you wnat the exhaust to stay hot? the heat in the exhaust gases would keep the velocity up and exit out the back sooner. wouldnt that be the reason for heat wrapping them and coating them? and if i am wrong on my thought, then you could just add inverted vents for the air underneath to draw the hot air out from the exhaust and engine bay. but not too much, because then that would void out the flat bottom that has been made right? </TD></TR></TABLE>

yeah you have to compromise between venting the air and keeping verious components cool enough that they dont fail.

i dont know about keeping the exhaust hot to make power, thats news to me. its allways been my understanding that header wrap was to avoid other parts around the exhaust from getting heat soak. i didnt know it had anything to with what you were describing. i cant see header wrap raising the temp too drastically to make such a marked improvement on velocity but i am in no way an expert when it comes to engines so i could be wrong.

this is one of the big reasons why having a mid engine car is really benificial. you can have the smooth underbody that you desire, and the hot air from the exhaust and everything else can just vent directly out of the back.

back to the topic of front engine cars...as i said earlier i believe that free flowing air ecountering the engine components is not a good scenario in terms of aerodynamics. i would rather completely isolate the engine bay and use one or several small elexctric fans to blow air across the various compnents and then the air will vent through the hood.

if you have to use the air outside to cool your underhood compnents then limit the amount of air that comes in and just have a small opening and still keep the bottom sealed up and let it all vent through the hood, not the underbody

Niles

I don't want to get into the debate over exhaust velocity/heat/mass flow in this thread, I think it would be too off topic. The reason I mentioned letting *some* air flow over the manifolds is that if they get too hot, they can crack. This happens to some manifolds that have been wrapped or coated because they get a bit too hot and the stress from the heat related expansion causes cracking. (Both from hoop stress and just from runners "moving" a bit differently when heated. Metal can also become hardened and loose flexibility if it is rapidly heated and cooled) A really well designed and developed manifold usually won't have this problem, but not many fabricators have engine dyno's they can run a manifold on for hundreds of high temp heat cycles, so sometimes its best guess.

I love that image. Engines running at high speed for a while make some pretty hot exhaust gas. (That's an F1 engine, I just posted because pictures are neat, and make people want to read the caption )

Also remember that any pumps in your compartment will, because they pump fluids and air under pressure, make heat. A little bit of air is all they have cooling them. Unless you have some trick water cooled P/S and A/C pumps They're not as important, but if you completely seal off an engine compartment, gotta make sure that heat has somewhere to go...

Also electrical wiring's resistance goes up with temperature. Your alternator would have to work just a bit harder if it was 100 degrees warmer, your spark would be a little weaker (although probably not significant because of the high impedance wiring used to supress RF interference) . How much harder? ummm, I just got back from working all day and would rather work on my car than figure it out, but anywho... My point is there are reallly good reasons for letting some air bounce around in there, and getting the rest of it an easy path out.

Damn my rambling tendancies.

gldndrgn14

iTrader: (1)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mr.E.G. &raquo;</TD></TR><TR><TD CLASS="quote">

this is one of the big reasons why having a mid engine car is really benificial. you can have the smooth underbody that you desire, and the hot air from the exhaust and everything else can just vent directly out of the back.</TD></TR></TABLE>

that is why i have a mr2 also

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Niles &raquo;</TD></TR><TR><TD CLASS="quote">I don't want to get into the debate over exhaust velocity/heat/mass flow in this thread, I think it would be too off topic. The reason I mentioned letting *some* air flow over the manifolds is that if they get too hot, they can crack. This happens to some manifolds that have been wrapped or coated because they get a bit too hot and the stress from the heat related expansion causes cracking. (Both from hoop stress and just from runners "moving" a bit differently when heated. Metal can also become hardened and loose flexibility if it is rapidly heated and cooled) A really well designed and developed manifold usually won't have this problem, but not many fabricators have engine dyno's they can run a manifold on for hundreds of high temp heat cycles, so sometimes its best guess.

I love that image. Engines running at high speed for a while make some pretty hot exhaust gas. (That's an F1 engine, I just posted because pictures are neat, and make people want to read the caption )

Also remember that any pumps in your compartment will, because they pump fluids and air under pressure, make heat. A little bit of air is all they have cooling them. Unless you have some trick water cooled P/S and A/C pumps They're not as important, but if you completely seal off an engine compartment, gotta make sure that heat has somewhere to go...

Also electrical wiring's resistance goes up with temperature. Your alternator would have to work just a bit harder if it was 100 degrees warmer, your spark would be a little weaker (although probably not significant because of the high impedance wiring used to supress RF interference) . How much harder? ummm, I just got back from working all day and would rather work on my car than figure it out, but anywho... My point is there are reallly good reasons for letting some air bounce around in there, and getting the rest of it an easy path out.

Damn my rambling tendancies.</TD></TR></TABLE>

well said

beepy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mr.E.G. &raquo;</TD></TR><TR><TD CLASS="quote">
if you have to use the air outside to cool your underhood compnents then limit the amount of air that comes in and just have a small opening and still keep the bottom sealed up and let it all vent through the hood, not the underbody</TD></TR></TABLE>

Yep. This is what the air dams on road race cars are all about. #1 cause of drag on a car is air entering the engine bay and having to divert in various directions to get back out. This is arguably more important than the turbulence caused by an uneven underbody surface.

mrlegoman

So I guess you would now have a legitimate excuse for getting a ricey EVO hood?

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mrlegoman &raquo;</TD></TR><TR><TD CLASS="quote">So I guess you would now have a legitimate excuse for getting a ricey EVO hood?</TD></TR></TABLE>


ehhh, not exactly. when i mentioned hood vents i was refering to something that vented up and to the rear. the hood on the evo is more for getting air into the engine bay, and the vent i was describing was more about getting air out from the engine bay and having it rejoin the air flowing over the car.

something like this:





both of those are perfect examples of what i mean when i say that the engine bay should be isolated from outside air. the way thier radiators are set up keeps all of the hot air from the radiator out of the engine bay which probably cuts down substantially on heat under the hood not to mention that the air that flows across that part is hitting a more favorable angle for downforce. both of those are rear wheel drive and unless you have a long front end like that this setup probably wont work in a civic, unless you get really creative.

here is a more realistic example for a street car:



these vents dont provide quite an islotaed path for air flow across the radiator, but it should be enough venting that you can completley block off the bottom of the engine bay and not let any of the air escape through the bottom to interfere with your aerodynamic plans. this is more ideal for most people since it allows you to keep the stock radiator mounting setup.

all of these axamples of vents have one thing in common. they let the air release far enough to the front of the car that the air isnt getting mixed up with the complicated flow that occurs at the base of the windshield as niles mentioned earlier.


also mrelegoman, here is a site that should be right up your alley:

http://thebricktestament.com/

mrlegoman

Thanks for the write-up! Good pics.
Thanks for the link too. I never knew such a site existed.....

RMF

There is more going on there than you think.First the big one in the middle isn't a vent.Its more like a wing .It puts down force on the front of the car.And the vents are on the top because heat rises and hot air going over the car is faster than cold.The car will go faster with the hot air going over the car body.

Mr.E.G.

you're preaching to the choir man. as i allready said im keeping explanations simple since this is a confusing topic. but just in case you missed it

i didnt go too far into it since i was offering this as an example of what i described a few posts back about isolating the radiator from the rest of the components under the hood and not so much me pointing out every possible aspect of the picture.

and not to be a dick and correct you, but its nothing like a wing. or to be more accurate, it is no more like a wing than to say the entire shape of the car is like a wing. it is simply a more favorable angle which causes some deflection of the air that passes over that section which creates a high pressure area. but i have the feeling that you know this allready and that you were 'correcting" me more to be a smart ***. if im mistaken then i appologize and i think we should drop it, and if i am right then hopefully you understand now why i chose the words that i did and i think we should drop it. so yeah either way, this thread will not benefit from a pissing match. especially since im smarter than you and i will win

for those of you who arnt that familiar with aerodynamics think of the normal shape of a corvette and then look at the section where the radiator and ducting are. basically imagine the section on the front most portion of the nose (where it says compuware) imagine that that section isnt there and you will see how the portion with the ducting is just a big sloped section that comes off of the front splitter.

here this might make a little more sense than my rambling on and on:




imagine that this pic is a cross section of the corvette. the gray thing is the radiator and the part above the radiator that looks like a wing is NOT A WING i stress that because it looks like one, but thats just due to my shitty microsoft paint skills

that piece represent the "fake" piece of the nose of the car. let me explain. this car is a purpose built rcae car but the reason why it looks like a corvette is because they are trying to sell the image of a corvette. this is in no way a real corvette. its a tube frame race car that looks like a corvette. a corvette is not the most ideal aerodynamic package. but since that goal of this car is to be a fast corvette type thing they cant just completely alter the shape of the front end.

if they could it would look more like this:



in this example it is easy to see how the sloped front end shape deflects air in upward direction and how this nose shape could be close to ideal.

well back to the situation that actually happens...

it still has to look like a corvette so this portion:



is added and the corvette shape is still there.

now using our imagination again, imagine that that piece wasnt there and the nose of the corvette would bare a strong resemblence to this:




which is basically big fenders on either side of a sloped nose. (take this example with a grain of salt because as you might have noticed there is no front splitter on this porsche, it is using a slightly different concept to generate downforce. in other words just take the example of the sloped nose but ignore the absense of a splitter.)

now as i mentioned the corvette has the "fake" piece which doenst really do much aerodynamically. however the radiator needs something to hold it in place and the car needs a front mounted radiator so this is a good trade off. here is another example. a ferrari f50.


here you can see the radiator and the dual ducts through which the hot air vents.




again another example of where the top part of the nose isnt really doing much but since there is a radiator in the equation it is obviously necessary in both of these situations to have that piece.

here is an example where there is a piece used above the lower nose sction that actually does have a pretty big impact aerodynamically speaking. in this case its a wing mounted on the nose. obviousely this would make more downforce if they incorporated an aerofoil shape into the top nose piece of that corvette but it would look a bit "uncorvette" like with one these on the hood



now beofre you ask why you dont see more cars with this type of setup let me just say that part of it has to do with rules but the other part has to do with the fact that it is a ******* pain in the *** for anybody who doesnt have a bazillion dollars to spend on testing to get it right. wings can complicate things, and usually on closed wheeled cars the pressure on the front surface of the nose can make enough downforce and too much front down force can be a pain in the *** to dial in. in other words with so much undisturbed airflow in the front and such high pressure its "easy" to find downforce without a wing. but if you want to get an uber amount of front downforce you have to be able to balance it out with a **** ton of rear downforce and since the flow is disturbed by the time it gets back there it takes a big wing which mean more drag and blah blah blah. its all about compromising.

one last example of some innovative front venting/ duct work. here is an aston martin race car that doesnt have a good front nose shape from factory so they got inventive and rigged up a radiator setup similar to the cars pictured above only on the tip of the nose it has a duct type setup which uses the same principle to generate some down force as the radiator duct setup but its smaller and obviously doesnt have a radiator in it.






so yeah, sorry to go on for so long but i just got wrapped up in it.

and again I am deliberatley using general statements and simple explanations on purpose

i for one hate when i participate in a topic where i dont know what the hell they are talking about but to the 2 or three people that do, they talk way above everyones heads and nothing is learned. certain suspension topics for example. i get lost in them and i really want to keep this understandable as possible.

Mr.E.G.

also if anyone ever needs any car pics i have a ton saved to my computer that i have collected over the years, so feel free to hit me up if you are looking for a certain pic. i may not have it, but i just might as well.

tek_civic

nice description. i did a fairly large paper on automotive aerodynamics, i learned a lot during the research. but like they say. the more you learn, the better you realize that you know nothing at all.

EDIT:

Take a look at this drawing i made. please tell me what you think of my idea. ill explain it below.

so its pretty much self-explainitory but anyways. what i was thinking of doing is sealing the underpan of the car(in this case a crx) no air enters the undercarriage from the engine bay. instead the air enters through the normal radiator openening and directly after the radiator(with a push fan, no pull) is directed into tubes of ducting which run through the cabin all the way to the back of the car where there is a natural low pressure area at the back. the radiator would have a shroud that would only allow the air to leave through the ducting.

i also wanted to add a splitter or air dam to the front to minimize the air that enters the under pan area. of the air that does enter under the air dam i wanted to remove the high pressure by again routing air ducting to the rear of the car at the low pressure area. pickups on the underside would be standard NACA ducts.

if needed a small lip on the rear of the hatch could be used to create an even larger LP area behind the car to help with the HP comming from the ducting.

in theory this would decrease the drag coefficient by equilizing the LP area behind the car(low drag signature too=no drafting), it would also decrease the pillow of air in front of the radiator opening. there would be less air under the car and if designed right it could even be a LP area creating a suck rather than a float effect.

things to be considered: size of front rad opening, as well as radiator size(width). piping size and routing. wether or not to join all ducting in cabin or run seperate ducts for each pickup. where to exit the rear of the car. engine bay temps, maybe a little air directed into engine bay that leaves via rear of the hood(shimmed hood), or louvers.

well let me know what you think about my ideas. which are possible keepers, what needs a little help haha. thanks


Modified by tek_civic at 2:50 AM 6/6/2006

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tek-civic &raquo;</TD></TR><TR><TD CLASS="quote">nice description. i did a fairly large paper on automotive aerodynamics, i learned a lot during the research. but like they say. the more you learn, the better you realize that you know nothing at all.</TD></TR></TABLE>

indeed


Modified by Mr.E.G. at 4:39 AM 6/6/2006

tek_civic

here is another idea i just thought up. EDIT: duhh forgot to add the pic



basically it would seal the front and bottom of the car and relocate the radiator to the rear where it would cool via ducting in the floor of the car. this would also lower the HP area beneeth the car as said before. of coarse a little air would be needed for ambiant cooling of the engine bay. which was covered above.

also an oil cooler would be added on both setups to aid with cooling. either way cooling should be sufficient. i would expect the header/manifold to be ok in either setup unless running endurance races turbocharged. then more attention to manifold cooling may be in order.

thanks for looking.

GarageAlchemist

LMAO... sorry but i can't stop laughing...

tek_civic

what are you laughing at... are you laughing at my crappy pictures?? damn i knew i should have been an art major. lol

thehatchninja

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tek_civic &raquo;</TD></TR><TR><TD CLASS="quote">what are you laughing at... are you laughing at my crappy pictures?? damn i knew i should have been an art major. lol</TD></TR></TABLE>

no way man, you're just developing your style. I'm sure when you're dead everyone will have prints of these beautiful drawings.....they'll sell calendars, everything.

Rocket Man

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tek_civic &raquo;</TD></TR><TR><TD CLASS="quote">here is another idea i just thought up. EDIT: duhh forgot to add the pic



thanks for looking.

</TD></TR></TABLE>

I Dont really know to much about aerodynamics nor have I read anything and i probably shouldnt open my mouth but just looking at this one looks like a no no. If you wanted to vent the radiator in the rear of the car you would want air flow coming down not up ( I suppose you could run one of those cool roof scoops hehe). Even with front wheel drive and all that cause that just looks like you want to go for a trip. But I'd go with that design wont work

dfoxengr

yeah probably shouldntve


lol

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GarageAlchemist &raquo;</TD></TR><TR><TD CLASS="quote">LMAO... sorry but i can't stop laughing... </TD></TR></TABLE>

come on stupid, dont you know that ms paint is the standard for aerodynamic design in all forms of professional racing?

Mr.E.G.

ok, first off on thinking outside of the box. perosnally i think the idea of the ducting running through the car to the back is probably not a bad idea, but it is certainly complicating something that doesnt need to be that complicated. i will say that the idea of the suplementary ducts underneath the car will only complicate things further. if you were to apporach this idea i think that getting the primary duct to work would be tricky enough and the supplementary ducts on the underbody wouldnt really add any great benefit.

i can go on and on about the different possibilities and scenarios involving underbody airflow but lets just say that without proper testing equipment, which none of us will probably ever have access to, we should really focus on keeping the underbody extremely simple. employ a few known principles and dont rock the boat too much. i can pretty much assure you that the underbody ducts would just complicate things in such a way that you wouldnt be able to account for them.

aside form that, if the front radiator inlet and associated piping are sized corectly etc, then they suplemnetray ducts would not be necessary.

before i go any further lets discuss some of the ideal underbody situations.

there was guy named bernouli, you may have heard of him

the gist of bernoulis equation says that if air moves fast it has less pressure. if air moves slow it has more pressure. for example. take a sheet of paper from your printer and hold it in your hands like so:



this is the persepctive of you looking down on the paper whilc pinching it along the bottom two corners between your thumbs and your index finger.

the paper should drape over your fingers down to the floor like this:



then pull your hands up toward your mouth and blow acorss the top of the paper (not the bottom)



when you do this the paper will rise magically upward. well how does that happen?

im glad you asked . when the paper is sitting there the air on both the top and the bottom is at the same relative presure and the air is not exerting any force on the paper. gravity does its thing and the paper sags toward the ground. when you blow across the top of the paper, the high velocity air creates a low pressure zone. the pressure on the bottom of the paper is hogher than the pressure on the top, so the paper is forced upward by the higher pressure.

im a regular ******* bill nye the science guy.

ok so this clearly illustrates that the faster thee air moves the lower the pressure.

lets move on to the venturi effect. this is a venturi:



whats happening here is that you see the air flowing from left to right. the air enters the "inlet" of the venturi tube and that is the part to the far left where the air is crowding to get in. the long piece of the tube in the middle is the "throat" and the place where the air exits is the "diffusor".

a real life example of the venturi effect is your water hose. the hose diameter is about an inch, and suddenly you get to the nozzle (provided you hose has one) and it is a very narrow section of tube. and then you have the exit hole at the end of the hose. as we all know from spraying our siblings with the water hose the more narrow you make the "throat", (by adjusting the nozzle or if your using your thumb, by sticking your thumb into the flow further) the faster the water sprays out.

basically waht is happeneing is the water is building up in pressure in the inlet which causes the water in the throat to have a high amount of pressure forcing it through at high velocity.

the same thing applies to air since both air and water are fluids.

so to recap there is a big opening that gradually gets smaller. there is then a narrow section where the air is sped up due to the high pressure behind it, and then the air must return to normal speed and pressure and this is done through letting the air expand in the diffuser section.

now how does this apply to a car? well here is another example of a venturi:



in this example of a venturi you see that there is all of the same features only with a flat bottom. the road, as we all know, is relaitively flat. so the name of the game is making the underside of the car look like the top part of that venturi, since we obviously cant make the road look like that

i could spend hours talking about the different underbody configurations but it can all be summed up by saying that virtually every racing body doesnt allow this ideal underbody exploitation to occur, so there are numerous ways to do it through compromising. the rulemakers try to slow the car down, and the designers figure out new ways of extracting downforce.

but since we are talking about ideal (and more specifically ideal underbody for a closed wheel car) i will stick to that.



in picture A we see a profile view of the ideal underbody shape. the efficiency of this shape is improved if the underbody is sealed off on the sides to keep air from spilling in along the sides. the side skirts are represented in picture B in a skewed 3D form.

now lets talk about flat underbodies. when this underbody downforce thing blew up in a big way the racing sanctioning bodies outlawed the countoured underboady and said that the underbody had to be flat, which limits the amount of downforce. now there is a lot of confusion on the subject of flat underbodies. people often say "but i though flat underbodies were good for down force" this is a simple case of mixing up terms. FLAT and SMOOTH are too different things. flat means no sideskirts or venturi tunnels etc so the bottom of the car is littlerally flat. smooth means exactly that, smooth. the underside of a factory car is all bumpy and has all kinds of things protruding into the air flow. so a smooth underbody is better than this. but again smooth and flat arent the same thing.

now even witha flat underbody you can still make downforce by lowering the nose slightly more than the rear. this is like having a venturi shaped like this:



essentially the whole underbody except for the very front is like one big diffusor. its not as good as the contoured underbody, but its still pretty damn effective.

also i should point out that the anglesof the underbody in these pics is really exagerated. that steep of an angle would actually hurt downforce.

and when you hear of a car having venturi tunnels what they are refering to is a car that has a flat underbody along the cabin, but rearward of the rear wheels (most rules state that the bottom only has to be flat between the front and rear wheels) and then it has little contoured "tunnels" to create some downforce. why tunnels? because of packaging. most of these cars have longitudianlly mounted midship engines and the engine is mounted low. so the venturis go on either side of the engine/tranny. if the engine and tranny was ina different spot (which wouldnt make much sense for other reasons) then it would be more ideal to have one "tunnel" or countoured section at the rear of the underbody.

here are some examples of venturi tunnels:






could you make this work? sure. but i have two words for you... Side Inlet

if you want a rear mounted radiator you could just bring in air from the side of the car, like the radiatro inlets on an nsx.

here is an easier suggestion. its not really easy in most peoples terms, but its easier than cutting a hole in the bottom of your crx and mounting the radiator in the rear. a lot of porsches and ferraris use the radiator or oil cooler or whatever, mounted in the front bumper. the air enters the front bumper through and inlet and then passes through the angled radiator and out through the side of the bumper or it vents into the wheel well.




in the above picture you get a rough idea of what i mean, but i beleive thats something other than the radiator on this particular car.

it will be tricky fitting a radiator in a crx like that but you can figure something out. i tell you what, take some pics of your crx's engine bay and the radiator support and whatnot and ill see what i can macguyver up for you.


Modified by Mr.E.G. at 10:50 PM 6/6/2006

red92si

Porsche uses dual radiators mounted inside the sides of the front bumper fed by the inlet scoops that flank the large central oil cooler.

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by red92si &raquo;</TD></TR><TR><TD CLASS="quote">Porsche uses dual radiators mounted inside the sides of the front bumper fed by the inlet scoops that flank the large central oil cooler. </TD></TR></TABLE>

ahhhhh, i had it backwards. i thought the big one in the center was the radiator, and that the smaller ones were trans or oil coolers.

thanks for the info


Modified by Mr.E.G. at 1:58 AM 6/8/2006

mrlegoman

good chit

GarageAlchemist

LMAO !!!!! you guys are like 13 year olds playing D&D

I get plus 20 Downforce ! your roll.. ohh snap aeropodic backpresure !!! + 15 with a +4 stamina buff