quote Originally posted by rogergarrison: You might have some benefits if all the above are met, but any improvement, in my opinion, would be so slight, it wouldnt be worth the effort.

Didn't the above numbers show a "worthwhile" increase, just from the skinnier tires? It seems to me that drag co-efficents of +/-.01 seem to be measureably noticeable from the above numbers...

quote It would be like spending $5,000 to gain 2 horsepower....could be done but why.

Aluminum sheet is cheap. It's more like $50 max to gain 2 horsepower....

quote Originally posted by jstricker: There is no difference, aerodynamically, if the air is moving and the body stationary or if the body is moving and the air is stationary.

That's a lie. Wind tunnels are worthless too because the air moves; which is exactly the opposite of an airplane in flight.

Now, with that being said... The underside of a *stock* fiero is crap. tjm4fun IS right in one sense however... Because the car is moving and the ground is stationary, and there's little space between the two, there is a huge boundry layer above the ground (2" thick?). The stock underbody is screwed up enough to cause it to contact the underbody and cause all sorts of turbulence. This turbulence along with the shape of the nose will easily cause an excess pressure buildup under the fiero.

IMHO, if you were to remove the turbulence, specifically in the area near the front crossmember, and the engine cradle... (The fuel tank/passenger compartment floors could also use some smoothing, but they're not nearly as bad as the other two...) The air would be able to evacuate much easier. Now if you were to install a diffuser in the rear, which coincidentally follows the GT bumper quite well, you would more than likely have removed the lift. Maybe even created downforce, who knows.

I'll stand by the convergent/divergent theory until proven otherwise. Rake is also very important in terms of if the "throat" gets turned into a convergent or divergent section as well.

I'll leave you with the underside of an Enzo.

An excellent example Ryan with the Enzo of how this could work with the Fiero.

I agree that it's silly to start a flame war over this and I don't believe I've flamed anyone, if I have, I apologize. Some of the things written in this thread, however, are just wrong and I've tried to correct those.

To your point, though, in general, smooth is good. Smooth is less drag. The cost:benefit ratio is ultimately up to the builder and owner as to whether or not it's "worth it". The less serious you get about it, the less benefit you'll see, but that's all a part of the cost:benefit analysis that you have to do.

When you talk about sheeting the underside of the car several things come into play. For example, if you leave no other outlet for the cooling air through the radiator it will have nowhere to go but under the car. This can be a bad thing, but you can also use it. For instance, I can see a situation where if you leave a "tunnel" in the fuel tank area extending back from the radiator, then the cradle area open, when the air hits that open area it's going to be a low pressure area drawing the air up and out through the engine vents. I'd expect even more of that if there was more vent area. I'd still like to see a chin spoiler and side skirts to help direct the are and avoid mixing of the flows but then you run into the practicality of actually driving the car on normal streets to have them low enough to work properly. You also probably would not be able to vent ALL the cooling air in this way so you'd have to leave a place for it to go out the back of the car or some other direction.

On the DP cars, they use a tunnel like what I'm describing as well as venting radiator air out the front wheel wells, especially at the top, go get more air over the brakes (along with ducting just for that) and because it's an aerodynamically "dirty" area anyway it doesn't affect things as much. They also use a tunnel and diffuser which WILL aid in downforce if properly designed.

All of the thoughts in this thread INCLUDING MINE are simply musings, however. Air is a tricky thing and doesn't always behave like you think it's going to. There are some excellent computer programs available even to the hobbiest for designing airfoils and estimating drag but even they don't always work like you think they're going to due to the interactions on the air of various objects.

The only way to know what it's going to do short of doing a scale model and putting it in a wind tunnel is to try it and see what happens. I know that can be a time consuming and expensive propsition, but it really is the only way you'll ever know. I will say that you're not alone in thinking along these lines. I have an idea in my head to get cooling air from each side of the car, through the radiator, then out the wheelwells. I don't want air coming out a hood vent disrupting what I would hope to be fairly laminar flow at that point on the car. If I can keep the air from the radiator from coming out over the top of the car, as well as keep it out from underneath by venting to the wheelwells, that should keep turbulent and high pressure air out from underneath the car and if not creating downforce, at least not creating any lifting action. All of this would also rely on side skirts and a chin spoiler similar to what the DP cars use in the front end.

Air is funny stuff and we guess wrong more often than we guess right, so just enjoy the experimenting and let us know what you find out.

John Stricker

quote Originally posted by northeastfiero: Jstricker "If you want to argue terms like Bernoulli's theory, fine, but I don't think that's what the discussion is about. The discussion is about what happens if you smooth the bottom of the car." I started this thread to debate the feasibility of creating a smooth underbody would have on the aerodynamic and handeling of the car, while it`s nice to see everyone has different ideas on what this would / wouldn`t achieve it seems silly to start a flame war over it. Having read through everything if I sheeted off the entire underbody of the car with an inverted scoop on the underside drawing air in to the engine along with some side scoops, is there a chance that this might be benificial

Here are a few websites that explain the aerodynamics used in race cars. You'll even get a little history lesson.

Race Car Aerodynamics

Aerodynamics in Car Racing

Inside Racing Technology

For some reason, they keep mentioning the Bernoulli Effect... even when talking about wings.

quote Originally posted by jstricker: I presume you are doing a little chain pulling there since you included the smiley (and because I KNOW you KNOW better!)

It's all relative. I'd like to build a small scale fiero and wind tunnel to see some of these principles in action. I'd use one of those die cast if they were a bit bigger... I think the smallest you can use is 1/8 scale, and they are 1/18.

yes they mentioned the bournoulli effect, but a wing is a differrent factor. I believe someone already stated the car design has pressure under the lower body. I quess I misworded again, I am not infering planes wont fly. the ground has no effect on a wing when it is sufficently far from the ground. the car is within 6 or less inches from the ground, so turbulance and the "venturi effect" of the car moving along forcing air under it is greater than the bournoulli effect. the bournoulli effect is very fragile, as a plane stall, turbulance that causes aircraft to drop in the air is evident to anyone who has flown. there are far greater factors than bornoulli effect when dealling with a car and it;s close proximity to the ground. I think that is the point I was trying to make. And hopefully I didn;t upset anyone, I did not mean to flame or attack, just point out you can;t blindly use one threory to explain a complex system. I apologize if anyone took offence. sometimes I am less than subtle.
so let's let that die, and to stay on topic,
smoothing without screwing up cooling:
from the front cross membet back to the body floorpan is a rough area. lots of pockets, and protrusions. this is behind the rad exit path, so that could help if brought back to the pan. note if you were to pan the whole underbody, I would say you should take it back and meet up with the front heatshield and end that piece there. pickup again about a foot further backon the front cradle crossmember , to smooth out the oil pan and engine between the cross pieces of the cradle, and end it at the rear cradle member. that would leave the front cat area fully open, and the rear muffler are open. finish it off from the rear heatshield to the lower edge of the rear bumper.
I would crease it along the lenght to add strength, and if possible, actually make some channels higher under the floorpan, and drop down to cover the tubes on the sides. keep the edges as rounded as possible.
Chin the front, with an airdam, but not extreme (driveway pans love to remove them for you) don't drop the side skirts, I tend to think that the air drawn in from the chin created lower flow would need to be equalized to allow the cooling of the engine compartment.
Rake on the car does help. I noticed just lowering the front of my 88gt 1" made it feel more solid at speed on the road. but that could also be due to redoing the whole suspension with poly and higher rate springs But I always thought it felt more like it was floating a little, moreso than my 86 se that had a more noticable rake stock.

if you do pan the bottom, PLEASE PLEASE be careful while testing it!!!! what may not feel like any differrence at 60 mph could cause the car to go airborn at 90-100mph. without modeling things properly, it is guesswork, and could be very dangerous!!!

I had to say that, I never want to see anyone hurt themselves while enjoying their hobby!!!!

[This message has been edited by tjm4fun (edited 04-24-2006).]

It's hard to say. The problem you run into with wind tunnel testing is something called Reynold's numbers. Basically, to get an equivalent Reynold's number for something very small it's pretty hard to do at reasonable velocities and to get an accurate measure you need to be using equivalent Reynold's numbers. For those that don't know (and I suspect Ryan isn't one of those) Reynold's numbers pretty much explain the differences in testing due to scale and are dependent upon the size of the object and the speed of the airflow.

You could probably use any size as long as you matched the Reynold's numbers but there's a reason they like to use the full size versions for automotive testing because everything is 1:1 that way and you have all the real nooks and crannies that are on the real car. I would say that something along the lines of 1/4 scale would be much preferred if you're going to model and 1/8 would be the smallest practically usable.

John Stricker

quote Originally posted by ryan.hess: It's all relative. I'd like to build a small scale fiero and wind tunnel to see some of these principles in action. I'd use one of those die cast if they were a bit bigger... I think the smallest you can use is 1/8 scale, and they are 1/18.

quote northeastfiero said: An excellent example Ryan with the Enzo of how this could work with the Fiero.

Unfortunately, the Fiero's engine cradle will interfere with a proper diffuser. By "proper", I mean one that starts curving upward somewhere between the front of the cradle and the rear axle. I suppose you could start the up-curve at the rear edge of the cradle, but its effectiveness would be reduced. Plus, there's that pesky "droop" in the middle of the cradle at the back.

I'm not saying it can't be done. But I think it would take alot of work.

I saw the Rolex race. Couldnt believe he pulled off that pass just a few turns from the end. Great job !!!

quote Here is a pretty good shot of the front of the Suntrust Pontiac Riley. If you'll notice there are two vent areas, one on each side, that helps to vent the cooling air up high, where the air is already somewhat turbulent.

and:

quote The principle that make a Fiero less prone to lift in the front with an opening on the hood to let the air entering the front lower dam exit by the hood, is because the surface was in a climbing angle in the direction of the motion of the car that cause the air to build an high pressure zone and resulting in a force that help to push the front of the car on the ground....at the same time, the air under the front of the car have obligatory a lesser pressure....It work exacly like wing on an F1 or IRL formula car (with less drastic result) but it's the same principle.

I notice that the SunTrust car has the vents up high, but also directed around the car instead of up and overtop of the car. It also has the inclined rake for positive pressure on the hood area mentioned by perry rhodan. My understanding is that increased flow overtop of a car is undesired for lift and drag considerations. I surmise that hood venting a Fiero would be of increased overall benefit if it were done in such a fashion as to direct it around and not overtop of the car too.Relating to this and the smooth bottom topic of this thread, I have a few questions to ponder:
Imagine a Fiero GT with a larger than stock air dam, the opening in the air dam ducted to the rad, either a hood or side directed rad vents, and the bottom exhaust of the rad sheeted closed. Compare this to a Fiero GT with a the same larger than stock air dam, no hood or side vents, the opening in the air dam ducted to the rad, and directed under the car (stock), and the bottom of the car smoothed out as much as resonably practical.
Which configuration is likely to be of most overall benefit? One obviously has more undercar flow than the other. Cooling capacity should be about the same while moving. The pressure build-up and associated lift should be reduced in both by the use of the larger ducted dam.
Comments?

quote Originally posted by perry rhodan: I wonder , if you install some kind of fan under each of the deck lid opening that extract the air from the engine bay (thus the underside of the car) and propel it outside ....if you manage to extract enough volume of air at any given speed, this will maybe help suck the car to the floor....side skirt will help greatly

quote Originally posted by Delphince: I don't mean to be rude, but what?! The only way you could significantly exceed the stock level of airflow at speed would be to install hovercraft-grade turbines, and the horsepower required to spool them would prevent you from ever leaving second gear!

It's already been done ... more than 35 years ago. Have you ever heard of the revolutionary Chaparral 2J race car? It dominated the 1970 Can Am race series ... about 2 seconds a lap faster than any other car, including the all-dominating McLarens. Indeed, the "active ground effects" were so effective that they were banned after the 1970 season.

Incidentally, the "sucker" fans were powered by a separate 270 cc two-cycle snowmobile engine.





Practice trumps theory every time!

[This message has been edited by Marvin McInnis (edited 04-30-2006).]

Didn't the above numbers show a "worthwhile" increase, just from the skinnier tires? It seems to me that drag co-efficents of +/-.01 seem to be measureably noticeable from the above numbers...
(quote)


Worthwhile in this case............OK you get a .01 gain. So now you can take a corner at 120.5 mph instead of 120. You could get more by cleaning the bugs off the nose.

Its relative I guess, wouldnt be worth my while even if it was free.

Another example is some Dodge guys have run dyno runs with stock air cleaner box and just K&N replacement filter, then run it on the dyno with cold air intake installed that runs around $300. Gains were between 1/2 and 2 hp. You gotta decide if its worth $300 to gain a horsepower. The manufacturers claim things like UP TO 20 hp, but you rarely if ever will get their own stated max. Their not lying in their claim. you got between .01 and 20 hp.

Not flaming you for trying new stuff. But I think you would be creating more problems than you would cure. It may be a big improvement worked out right if you were talking about racing it in the Rolex series at 180+ mph but gaining nothing for driving on a freeway. You could see more of a gain in performance if you took out the radio, spare tire, carpet and uphostery, wheel center caps and anything else that would lighten the load.