I don't think venting under the car would cause problems. Explain how it would create lift. Air that now hits the nose and then go under the car on an unmodified 914 would now instead partially go through the radiator and then under the car. Front engined cars do this already. Am I missing something?

Andrew

Yes Dave, I have worked on these cars quite a bit.

The ducting in the picture DOES NOT go through the drivers compartment, but BELOW the drivers compartment. Hense the reason for the ducting out the bottom of the trunk (like the factory GT's did, but then going below the suspension cross member and UNDER the compartment where my feet go.

You seam to dislike a lot of things I do. People have been doing what Renegade does way before they got to it.

Please keep your negativity to yourself. This is a forum to share ideas, it might not be what you like, SO DON"T DO IT!

Thank you, Don.

Andrew, most cars that duct air downward don't do it for anyreason besides its the most convient place. The 914 suffers from this because you don't have the massive weight that the motor up front that most cars have with this type of ducting. So they aren't affected as much at 90mph. When i have taken off the 914 front bumper and any spoiler, i noticed the car would get more lift up front (taking into consideration that the weight of the bumper is gone also). The 914 also suffers from lift because its shaped like a wing to some extent, so any front air damn or splitter helps trumendusly to reduce front end lift. To see an extreme example of splitters, visit www.ultimate914.com. Its the Sheradon body kits, really cool stuff.

I just wonder if the amount of air going through the radiator would be enough to create lift. It is not exactly completely unrestricted so I don't think it would be any worse than a stock 914 which does have a valance that on casual inspection would seem to promote lift. Also the Lotus Elise has vents in the hood, so that is another possibilty, although it seems that you would feel the hot exit air in the passenger compartment with the top off/windows open.

Andrew

D'OH! For some reason, that never occurred to me... http://www.pelicanparts.com/support/smileys/blush.gif Sorry about that.

--DD

Andrew, you bring up many good points. If i were to do the ducting, my first choice would be to do as the Lotis Elise, cooling exhaust back onto the hood. I agree that it would be hotter air going over the hood, and in cooler climits would be nice to have the top off and hot air coming in, but as to the amount of hot air it would produce and ulitmatly make its way into the compartment after going over the hood and windsheild, i don't know. That air will mix with the other air that did not go through the radiator, cooling it a little. I figure for functionality as well as looks, its too perfect. I hope during my short track racing with the POC I will be forced need an extra cooler for the 3.2 6 (the stock cooler works really well, and more cooling isn't usually needed). I would love to do this modification with fiberglass bumpers and fiberglass hoods which would lighten the car even more.

Where on the front lid would you put the outlet? I know that there is a high-pressure area back by the windshield, but I'm not sure what kinds of pressure the rest of the front lid sees.

N.B., a local guy had an oil cooler setup on his Six that tried to vent through louvers in the front third of the front lid. It didn't work very well--they thought it wasn't getting enough air flow. So he replaced the lid and I think wound up putting GT-style ducting from the cooler to cutouts in the trunk floor.

Unknown if it was the placement, or the exact shape and area and so forth of the louvers. Or something else, even?

--DD

what if you were to duct it so the air would be channeled back under the car a little ways, not just pushed straight down? this would create a relatively laminar airflow, which wouldnt be much faster than the airflow already going under the car.

I guess a good way to visualize what i'm saying is it would be like taking a hood scoop and putting it upside down on the bottom of the car to disperse the air. Basically if you make the air "hug" the bottom of the car, its much better than having it smack into the ground and create a bunch of turbulance under the car, i would think.

And about the car being relatively wing shaped, in that case the biggest issue is the top side of the car, not the bottom side. Take an airplane wing, for instance. At least 75% of the lift on an airplane is from the wing being "sucked" upwards because of the lower pressure on the top side. The bottom side of the wing (or car in this case) is relatively flat, and lift generated from airflow underneath "pushing" the car up is pretty minimal. This is why a spoiler on the car works, because its basically a wing with a negative angle of attack, meaning if it were a wing it would be flying towards the ground.

one more thing, with the air dam you would have to fit on the car for airflow over the radiator, you will be generating a substantial amount of downforce, probably more than enough to counterract the small amount increased lift developed by chanelling more air under the car.

Wouldn't more air going under the car cause suction like stated in Bernuli's principle. For example, if you force more air through a straw than around it the straws sides suck towards one another and you get a funny sound as the sides vibrate against one another due to the lower pressure created in the straw. The only way I can conceptualize a trunk bottom exhaust causing lift is if the air coming out were directed straight down and were of a considerably stronger force, like a jet.
Just curious what yall think. I am not trying to say that I know if this holds true in our case or not.

I just realized the thread title...You have been hijacked! All your base are belong to us. Sorry, Mr Mueller.

actually you are right that speeding up the air under the car would essentially create a suction, because it would be creating "negative lift" if you will. but it would be very very minimal, unless the air was being sped up a huge amount.

my point was that if the air was directed straight down, it could smack the ground and then come back up and hit the body again, causing there to be turbulance under the car, not necessarily any lift. basically the car would just be jumpy, not just unstable.

I see, poo.
Also the way I described it as well as the way you described it would cause some turbulance.

I don't think i would blame it on the louvers, there is a low pressure spot on the front half of the trunk, and then a high pressure spot just before the windsheild. A NACA duct would be a much better choice in that low pressure area, its job is to create a sucking force (depending on wether you want it in or out) created by air flowing over. I personally would have twp big gapping holes like an F50.

Although you both have interesting concepts, lets keep to the more simplistic side of things. We're working in a feild (aerodynamics) that i can safely say non of us has taken any formal lessons on. That aside, lets use examples that others who have taken these lessons have made the cars today very efficient. And please speak up if anyone in this conversation is a airplane pilot.

We can all agree that a car is not an aeroplane, but wings on cars are derived from them. So the fact that a car will have turbulance from wind and the ground, cannot be directly compared to airplanes flying high in the sky (only on takeoff, but then thats a whole nother section).

Lets stick to what is obvious. The air flowing over and under the car. Like a wing, the air going over a car has to speed up to meet with the air below it, causing low pressure like on the top side of the wing. Granted that the object must be light enough to take full advantage of this low pressure event. Now what happens when there is no air going under the wing? I do not know this answer, i can only speculate. But what i do know is that low farings and spliters are very common on race cars... lets take for example, the very sucessful Le Mans winning Audi R8. The splitters are almost on the ground, and with the assumption that they don't touch because of ground irregularity abrasion and the suspension needs to have some room to work. So there is some air that can get below the car.

Now lets take an example some years ago in F1 or Indy. I remember being told that one of those exotic race cars used to have a wooden board bolted to the bottom of them, and after the race, the winners would have to take off that board to assess how much was left. If the board had been scraped beyond a predeturmined width, they that team was disqualified. The point of this, to keep everone up off the ground a certain amount. Why? because the less air you have going under you, the less overall lift your car will expericance. How? I don't fully know. But its a logical, consistance reason.

You take air from the front, push it any where you can BUT down under the car. Now for the air that does go under the car due to ride higth clearance, people came up with ground effects. On the bottom of every Ferrari produced today, is a type of ground effects in work. In essence, you make the car perfectly flat. This keeps any air from tumbling under your car, caused by your car... why? because it DOES hinder handling.

Now with aerodynamics involved, we take that flat panel under our car, and rake it at a 1 deg slope, lowest in front, higher in back. Random extreme example: The air now enters at 3"x48" of clearance up front (144sq in), and over the distance of a 15 foot long car, it now exits at about 6"x48" in the back (288 sq in). The set volume of air entering the front of the underside of the vehicle must expand to fill the void. It cannot do it that fast, so the air then creates a vacuum, pulling the car down.

This example works great for the mid to rear section of a car, but the front i'm not to sure of. I just understand a lot of the concepts, but i appologize for not having all of the knowledge associated to finish a quality explination. But what i do know is that the less air that goes under the car, or the more air you can direct around and over, the better handling through downforce you get... which i know we all realize.

I hope that helps, even if it creates more questions. The thing about the straw does not apply here, the section between the wheels is not closed off to create a tube section.

What is the advantage of using a 228mm clutch over the (stock?) 215mm clutch? Kennedy Engineering has Stage I pressure plates for both sizes and both will hold 230 ft*lbs of torque ...

I'm going with the larger diameter unit mostly 'cause I'm getting a great deal on a low mileage 228mm pressure plate so cost wise I am not spending any extra money.

My KEP catalog just came in the mail. Lots of good information in there. Man, I'm pretty excited about this engine swap. If I can make it work, I think it will be cheaper than a hi-po 2270.

http://www3.telus.net/public/alpine65/KEP.jpg

i just went out and looked at a couple things on the car, and it looks like the best way to go would actually be putting the exhaust out the fenders, behind the wheel. not only does it avoid the whole aero lift thing, but i would think it would also have the added advantage of cooling the brakes a little bit. (the air that has flowed over the radiator is hot, but not that hot)

i think the one thing we were all overlooking is the fact that, yeah a car does develop lift, but almost all cars have a forward rake, meaning the direction of total lift would be down, hence downforce. i am a pilot, while not an airline pilot, but i do know a few things about aerodynamics, and while the air flowing under the car would create only a minimal amount of lift, it would probably be enough to offset a good deal of the downforce generated by the top of the car (think Lamborghini Miura or, to a lesser degree, Ferrari GTO) making it feel very "floaty", for lack of a better word.

Forward rake will not turn lift into downforce. A wing at a (slightly) negative angle of attack will still generate lift. It will develop much more lift at a postitive angle of attack, of course...

Keeping some air from getting under the nose of the car will keep it from getting as "floaty". Some of my racer freinds confirm this with 914s--they tell me that after about 110 MPH, the nose of the car was noticeably light. After they installed deeper air dams, the nose was much more planted at high speeds.

Most aero effects are irrelevant for any street-legal speeds this side of the autobahn. Which, of course, doesn't mean that a high-powered 914 will never see those speeds....

I think it would be instructive to ask some people who have V8 914s (and 914s with large nose-mounted coolers) where their cooling air exits, and how their car feels at various speeds. That would probably give us much better info than trying to figure out generalizations from basic aerodynamic laws. Aerodynamics, an aero engineer once told me, is the most empirical and least-intuitive of all the engineering disciplines. Real-world results are probably a better way to judge...

--DD

What you could do is pack the whole underside of the car with bondo and sand it into the shape of a large inverted wing to create downforce. :)

Dave, I couldn't agree with you more. In my examples, i tried to use cars that are on the market using these aerodynamics. Although the 914 is a different body design from most, its still a mid-engined layout, like most exotic sports cars today sporting ground effects which are a result of real-world results... and i see no reason why they cannot be adapted to the 914.