Originally Posted by tek_civic
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.
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:
Originally Posted by 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.
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