I know that people install hood vents onto their Fiero to reduce underhood pressure and to increase high speed stability but would it reduce the aerodynamic drag (cd) of the vehicle? I tend to think that it would since all that that air that is being trapped will now flow out of the hood vent. What do you guys think?

My thoughts on the subject would be: Reduction in CD would result "if" and only if front end lift was either reduced or eliminated. You don't necessarily have to have a hood vent to accomplish that, air can be ducted out other ways.

[This message has been edited by California Kid (edited 06-10-2010).]

I have seen some openings in the area of the headlamps that can reduce the under hood pressure.
At speed that air pressure is what pops up your head lamp covers.

quote Originally posted by California Kid: My thoughts on the subject would be: Reduction in CD would result "if" and only if front end lift was either reduced or eliminated. You don't necessarily have to have a hood vent to accomplish that, air can be ducted out other ways.

that sounds proper.
if the air drag is creating less lift - this would mean there is less energy being created by the air flow - which basicly means less drag

Maybe I'm looking at things wrong, but if you raked the car a little bit, say half an inch to an inch higher in the rear, wouldn't that suck the air out better under the floorpan without cutting the hood?

In my head, it would create a low pressure zone under the car.. I'm not an engineer, though, just a tinkerer, so I may be way off here.

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Currently in the middle of my 88 + 3800NA swap

quote Originally posted by aaronkoch: Maybe I'm looking at things wrong, but if you raked the car a little bit, say half an inch to an inch higher in the rear, wouldn't that suck the air out better under the floorpan without cutting the hood? In my head, it would create a low pressure zone under the car.. I'm not an engineer, though, just a tinkerer, so I may be way off here.

The car is not low enought to the ground to do this.

The high pressure area for the most is a neutral zone and if anything is keeping the air under the car and it just passed under for the most part. Only so much gets in and the rest will just pass.

Having the vents does not hurt it as the air flow moves well and the air under the car is normal or cut based on speed.

There are more and different areas that would increase aero effect. Just look at what some of the aero managment that Ferrari has used on some of thier recent car as well as some other high end performance cars. Belly pans are the in thing and they all are looking for ways to move the air efficently under the car. What they are are doing is trying to make a stable car fast car by cutting drag while keeping some down force that was not created by any majore aero effect.

In other words get the air in under and out from under the car without adding drag. It is easy to create down force but to do so with out wings etc air managment is very important. It takes a lot of time to design and sort out.

One of the least aero things on the FIero is the tires and wheel well openings. Also the drip rails and rear window. My high profile HHR is about as Aero as the Fiero. This shows how much has been learned.

Also look at the tricks GM is using on the Volt. Some of the simple features add 7 miles to it's electric range. The edge on the end of the rear bumper added 7 miles alone. This design feature may find it's way on other vehicles.

[This message has been edited by hyperv6 (edited 06-11-2010).]

Wow. Yes, we have come quite a ways with computer modeling, etc.. Hmm.. Back lip you say? *ideas burning in my head*

quote Originally posted by aaronkoch: Wow. Yes, we have come quite a ways with computer modeling, etc.. Hmm.. Back lip you say? *ideas burning in my head*

Check the vertical edge on the rear bumper corner. It is not much but it adds a lot.

Also check out the Volt based MPV they intro'd in China. It has a similar thing only pretty deep on the real D pillar.

quote Originally posted by fierofury: ... would [a hood vent] reduce the aerodynamic drag (cd) of the vehicle?

Interesting question. Theoretically, probably yes ... but the question is how much? In a practical sense, I expect that any reduction in drag would be unmeasurable at legal highway speeds or below.

A properly-placed hood vent will be exhausting stagnated "high-pressure" (we're talking about fractions of a psi here) air into the relatively low pressure area at the front of the hood, and that will reduce drag very slightly. You can think about it another way, too. For a finite surface, lift is always accompanied by drag. In fact, lift causes drag; such drag even has it's own name ... "induced drag" ... the drag due to lift. If you reduce the lift, you reduce the induced drag slighly. On the other hand, if the air is leaving the hood vent more-or-less perpendicular to the free stream, then that will create some drag of its own ("interference drag"). Again, in the real world I doubt that any change in drag either way would be large enough even to measure.

[This message has been edited by Marvin McInnis (edited 06-11-2010).]

quote Originally posted by Marvin McInnis: Interesting question. Theoretically, probably yes ... but the question is how much? In a practical sense, I expect that any reduction in drag would be unmeasurable at legal highway speeds or below.

Interesting...I would have guessed that a vent of some kind would make a decent reduction in drag.

I am very interested in the subject of drag and how to reduce it, especially when it comes to fieros. I am interested in stealth mods that reduce drag, such as mods that don't take away to much from the stock fiero look. An example would be an underbody tray, lowering, flush turn signal covers, etc... My aim is to reduce drag in order to reduce front end lift and to increase highway fuel efficiency. Speaking of front end lift, do front lip spoilers help out in that department? (Don't plan on getting one, just curious).

I like what fierosound did to his fiero in regards to underhood pressure. http://www.fierosound.com/moreMODS.htm (bottom of page) I might have to implement that into my car but I wonder if one vent will be sufficient or not.

[This message has been edited by fierofury (edited 06-11-2010).]

quote Originally posted by fierofury: Interesting...I would have guessed that a vent of some kind would make a decent reduction in drag. I am very interested in the subject of drag and how to reduce it, especially when it comes to fieros. I am interested in stealth mods that reduce drag, such as mods that don't take away to much from the stock fiero look. An example would be an underbody tray, lowering, flush turn signal covers, etc... My aim is to reduce drag in order to reduce front end lift and to increase highway fuel efficiency. Speaking of front end lift, do front lip spoilers help out in that department? (Don't plan on getting one, just curious). I like what fierosound did to his fiero in regards to underhood pressure. http://www.fierosound.com/moreMODS.htm (bottom of page) I might have to implement that into my car but I wonder if one vent will be sufficient or not.

I have a coupe nose and an air dam removed my lift. The hood vents removed the rest of the lift. It really is easy to do.

One other factor on the hood vents is the shape of them. Do they add or stay neutral in the drag count of the car? some shapes can add more CD to the car than they help.

There are plain things a Fiero owner can do to help their cars. But most things would need tunnel time and a engineering degree to really know or test. What works on some cars does not always transfer to others.

Bump to revive this thread for the Fiero Endurance racers.

I have always looked at the stock airflow behind the radiator as a design flaw.
Granted the GM engineered were not building a race car and needed to fit the spare.

On the road you will rarely have an occasion to hit triple digit speed.
Let alone in traffic or in the rain.

What is the best way to keep the nose down at speed and not break the bank?

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"Now you too can see in the dark."
http://projectorretrofit.com/

quote Originally posted by hairballrm: Bump to revive this thread for the Fiero Endurance racers. I have always looked at the stock airflow behind the radiator as a design flaw. Granted the GM engineered were not building a race car and needed to fit the spare. On the road you will rarely have an occasion to hit triple digit speed. Let alone in traffic or in the rain. What is the best way to keep the nose down at speed and not break the bank?

Hood vent, air dam and lower the car. Under car air managment is the key. The coupe nose make lift and the lack of a vent makes a high pressure areas both bad for stability. The GT nose even has a little slant up on the bottom that a lower lip entention helps but make it more difficult to drive on the road.

The Fiero for the most is a crude un refined aero car. Aero was really just coming into the picture at this time and they have applied much since then.

My Hood vent and air dam on the coupe nose has made my car stable where is used to have a lot of issues.

I did not lower the car but the lower the less air is under the car.

[This message has been edited by hyperv6 (edited 07-16-2011).]

I would say a hoodvent really helps. Going as fast as my car will do on a windy day, the wind snapped my headlamp cover off and created a big crack in the hood.
Really some power in that airflow! That never happend again now that i have a hoodvent.
I dont have a really sportscar type deep hoodvent (they go almost till the bottom of the car), but still so deep i had to slice off a small part off the inner front compartment structure and lower the coolant bottle.
To get better aerodynamics a really deep hood vent would be much better i think (mine is about 3 inch in the middle). I didnt want to cut a big hole behind the vent, making that bigger would also help ofc.

Also, on a day it rained with fine sand in the rain the airflow behind the hoodvent was very visable and went till the end of the hood.
Bad thing was that it was a much more chaotic pattern then i would have thought, so alot to improve there, guess there is more to it then just cut and build a hood vent.
On the rear of the car the lines all went forward towards the rear window, that was fun to see. Guess the spoiler really helps creating an air bubble behind the window.
Biggest improvement aerodynamically i think would be a deep hoodvent (cutting up the front compartment) and to replace the spoiler with a whale tail type or make some sort of louvres at an angle between the rear pillars.
Now that would look cool aswell!

dont have a good picture on this pc but below my car with the hoodvent

[This message has been edited by Edwin (edited 07-16-2011).]

During the rebuild, my '86 received a vented hood, and there was a MAJOR difference in the feel at speed. With the stock '86 body, I could feel the front want to go airborne at 75-ish. With the Formula rebody and the added vents, high speed stability has gone through the roof.



I think if you're going to use vents that help direct the flow of air OVER the car parallel to the air stream, the drag should go down noticeably. I don't think that ejecting the air pressure perpendicular to the air flow is going help much if at all, and may even be a hindrance to increasing economy.

I've often wondered what it would take to mold and modify "scoops" similar to what's on the Ram Air TA's

Small opening at the nose and a short, wide opening at the windshield, with vents similar to mine in the hood. Put 'em on a 87-88 coupe/formula.. I bet they would look awesome if done right.

But, I'm not an engineer and this is all speculation..

I remember during my aerodynamics tests (with a camera rig and short pieces of string taped all over the hood), I noticed that my hood vent was creating turbulence in the center area of the hood. Turbulence creates drag. So I don't think my big hood vent was helping the car's drag coefficient. But it was definitely improving front downforce.

You also have to consider that after the air exits the hood vent, it hits the windshield. The more air you have flowing over the hood, the more air you have slamming against the windshield. That said, if the hood vent were to flow just enough air to create a properly sized pressure bubble in front of the windshield, the bubble would smooth out the airstream going over the top of the car. THAT would reduce drag. But the R&D for such a vent would require the use of a wind tunnel, and some sophisticated equipment.

For us average joes, I think venting pressure through the wheel wells, and/or using small hood vents, would be the best way to vent underhood pressure without generating much drag.

[This message has been edited by Blacktree (edited 07-16-2011).]

Cool fiero Edwin.Put a similar vent in my hood also, cut into the cross member @ top of tire well & dropped front edge 6", similar to a
Gt-40 style. May I ask, the blue car next to your fiero-what is it? Any other pics? It just looks slippery. Thanks-Rick

quote Originally posted by aaronkoch: Maybe I'm looking at things wrong, but if you raked the car a little bit, say half an inch to an inch higher in the rear, wouldn't that suck the air out better under the floorpan without cutting the hood? In my head, it would create a low pressure zone under the car.. I'm not an engineer, though, just a tinkerer, so I may be way off here.

That is fine but the problem is the way the radiator cooling is designed. If you lower the front of the car and put an air dam on the front, You would be reducing the flow thru the radiator while reducing under the car pressure. The air comes from under the nose to cool the radiator. It is the air behind the radiator that builds pressure and causes the front end to lift at high speeds. (as well as pop open the headlight covers.) To reduce drag and lift you need to reduce that pressure behind the radiator. A hood vent is one way. Some folks have opened up the sheet metal behind the headlights to duct the air/pressure away as well. Typically the air is ducted by two small areas on each side of the front trunk seal. These channels are not large enough to move the air at high speeds.

Once you relieve the pressure behind the radiator you will reduce front end lift as well as improve cooling efficiency.

Heres my somewhat plain and simple reply to this response. Venting out the front hood is one of the BEST improvments that can be made to the stock Fiero design.
I vented out mine, and the crusing improvements, at high sppeds, are GREATLY improved. My 87 GT hughs the road and stays low and steady. Combined with this, it runs much cooler as extreme heat gets to escape from that area. Next time your out for a drive, pop your front decklid, and pla ce your hand on the underside lid area right above the radiator after you park after a good long drive. You'll see for yourself how HOT that area gets. Theres no place for the hot air to go !
I used the dummy hood vents from a 95 Camaro. You know, the ones up high on the hood close to the windshield. I gutted them out, then placed them in BACKWARDS on my 87 GT. I "glued" them in using J-B weld, which worked excellent for me.
Only thing, when I initally tested them on a open road highway, I blew out one of my 1/4 window sail panels while up around 110. So make sure everything else on your Fiero is tight and safe.
.... I would STRONGLY recommend this alteration, not to mention how "Cool" it looks.

To judge drag on a car takes more than just string and tape. One of the things that creates more drag is the tires on the Fiero. I read a long time ago how a GM engineer used a Fiero as an example and said the wider tires add so many more counts of drag. Also the roof rails and other things contribute.

The fact is the hood vents make the car more stable and kills the HP area under the nose of the car. The coupe nose generates lift at higher speeds and makes a light nose even lighter and unstable feeling. This is about air managment and it does not take string and a wind tunnel to help make this car feel and drive better. Hood vents have been a part of racing since the 60 and was one of the first things learned to make a car stable.

A good example of the force of the air pressure is driving at night I can see a large moth flying in the road before me. Once I get there he gets half way up the hood and the air from the vent will shoot him over my roof. As funny as it sound the vent has also worked well as a bug deflector a s few ever make it to the window due to the force of the air pressue coming out.

The air on the stock car for the most goes out under the car and not the wells. It is not an efficent design but worked well on a stock street car. I assume GM did not want to have to deal with the realated warranty issues that could have happened with more water, dirt, mud and other things getting into the front compartment. This is what killed the side scoopes on the first gen Fiero Coupe.

All I can add is the Fiero with the addition of the vent and air dam is a very dramatic difference in how the car feels.

quote Originally posted by Edwin:

Edwin, more information on the blue car in the picture. Tks

Rob

The car is a TVR Tuscan.
Most summers friends and i go to the nurburgring to look at the track, the cars and to drive a few laps ourselfs.
Always a great atmosphere there and always lots of special cars. That weekend there also was a TVR Sagaris.
Cant seem to find the rest (not fiero) pictures i made so here's one from google.

@rick you have a picture of the deep hoodvent you made? I wanted to still be able to store the roof glass in the front so i couldnt cut deeper.
If i have to work on it again im not sure i could resist tho, those really deep vents look great!

On topic of aerodynamics, a roof spoiler might also help. I think the worst aerodynamic part of the Fiero is the rear window.
A great aerodynamic car was the opel calibra. My brother used to have one, i believe it has a drag coefficient of 0.26 and the car came out like that in 1989!
Great handling on it aswell, one of my fav cars aswell if the Fiero didnt look so sexy!

[This message has been edited by Edwin (edited 07-17-2011).]

quote Originally posted by Edwin: Below a roof vent to keep the air bubble behind the rear window in place I believe its also available for the fiero? And a louvre idea on a esprit, anyone ever made something like that for a fiero?

The rear deflector was never offered for the Fiero but someone may have adapted one for it.

The rear louvers were offered for a while for the coupe. Not many survived the 80's.

Edwin; Haven't forgot ya-too many folders of pics, not labeled either, computer skills r marginal @ best. I'll take new pics & see if I or wife can send them.


EDIT: 6-20-11,10:08 pm. Edwin, can't get Pennock image thingie to work. Send an E-mail to fieros4u@sccoast.net Then
I can post pics to your E-mail. Rick

[This message has been edited by Rick Morehouse (edited 07-20-2011).]

thx Rick for going through all the trouble getting a picture!
Mail send!

I couldn't drive over 70mph without feeling like I was driveing on ICE.
once I lowered car and upgraded suspension parts I didn't have the floting feeling anymore but when I reached 88mph........
my headlight doors would open sending me back to the future.

Sent pics--I hope. Let me know plze. Rick

Yes there were rear louvers available for the fastbacks, here's a picture of Kameo Kid's car:

quote Originally posted by Sourmug: Yes there were rear louvers available for the fastbacks, here's a picture of Kameo Kid's car:

These were sold for short time and even fewer of these survive. Most of the lovers were beat to death over the years and most people would just take them off once they broke. Many have not been made since 1990. You have to remember these often were on daily drivers and they just did not hold up well to being opened and shut a lot. I wish I had stock piled a lot of these parts when many were closed out year ago.

There also were some plastic ones out there one just stuck to the rear window. Most of the plastic ones looked as cheap they were.

http://www.youtube.com/watc...Gq70&feature=related
http://www.youtube.com/watc...cRdc&feature=related
I found a bunch of videos labelled as Fiero Aerodynamics some don't really explain much but might inspire your modifications.
I was going to start new thread on it but will suit this one.

quote Originally posted by Edwin: Most summers friends and i go to the nurburgring to look at the track, the cars and to drive a few laps ourselfs. Always a great atmosphere there and always lots of special cars.

I miss going to the Nürburgring! http://www.yellowfiero.com/...ixold/0906/index.php

quote Originally posted by hyperv6: To judge drag on a car takes more than just string and tape.

Tuft testing is a lot better than nothing. At least you'll get a general idea of what is going on with the airflow.

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Norm Vandermee