How can we lower the drag coefficient of an 87 fiero gt fastback.
I want to get the lowest drag coefficient to get best gas mileage at around 75 mph. Would a F355 front end be better? I've seen someone say that taking the wing off gave them 2 mpg more and the fiero books say you gain .007 when you take it off. What can be done to help it get lower?

lower the car

narrow hard tyres help both rolling and air resistance

hood vent helps flow

bigger rubber under car front diverter behind the rad

true that taking the spoiler off reduces drag. but having it there helps stabilize the car at higher speeds. I rather lose some drag co. for vehicular stabilization..

Visit EcoModder.com. There's a list of things you can do to reduce drag/air resistance and otherwise try and maximize your gas milage. Our Fieros have a lot of room for improvement in such areas.

quote Originally posted by Ryanstalin: true that taking the spoiler off reduces drag. but having it there helps stabilize the car at higher speeds. I rather lose some drag co. for vehicular stabilization..

Wrong... The spoiler was put there for fuel economy reasons.

From a similar thread on the subject:

quote Originally posted by Bloozberry: Road & Track November 1984: "For those aerophiles among our readers, the following will be of more than passing interest. The original Fiero with 13-in wheels and tires has a Coefficient of Drag (Cx) of 0.377; add the 14-in wheels and tires and that figure climbs to 0.406. With the pace car nose and 14-in wheels and tires the coefficient of drag drops to 0.372 and falls still further to 0.350 with the addition of the rear wing."

quote Originally posted by skuzzbomer:

I would not have guess that, but, sweet!

Can you actually feel the difference in handling with the spoiler vs not having it? I ask because my car came with it's spoiler off and I've never put it on because I like the look lol.

No, you can't feel the difference. The spoiler only smoothes the airflow off of the back of the car.

Change the rear section to the notchback style as it has a lower c/d than the fastback. Leave the rear wing on as it reduces c/d. [don't believe me, look it up. The lowest c/d from the factory came on the 84 indy, 85 gt, 86-87 se WITH rear wing] Lower your car. Run narrow tires. Increase the size of the chin spoiler. Chop the top. Get smaller more aerodynamic side mirrors. Run full disc wheel covers. Replace sunroof top with solid roof/go to smooth side mouldings to further smooth airflow [these last two are probably negligible improvements]

If you want better MPG in a Fiero, the first/best place to look, is an engine swap. Or a whole car swap. An 87-88 coupe 5 speed will get about 42-45 MPG on the highway.

People will list things all the time about how a hood vent, lowering, front fascia, tires, or whatever else might change the drag coefficient by about 0.001, but so far the only completed, functional change to a Fiero that nets any significant change in MPG, that's been done on this forum, is drivetrain swaps. If your car is an automatic, swap in a 4t60 trans, or convert to manual. Convert the ECM to the newer 7730, and switch to digital cruise control. Or install an Ecotec, 3800 Series II, or LX9 3500. Even the newer LS V8s can net better MPG than the stock 2.8.

well the back is open close it so that would reduce the drag allowing the air to flow over smoothly.

the problem with doing this will increase the heat in the engine area but i have seen it done to a 4.9 conversion and he added air scoops to the wings on the side but he ran them to the air cleaner. I think a nissan back glass was used to do this.

adding the formula front clip is a good idea and adding a front hood scoop to allow air to flow better thru the radiator has merit ground effects kit would work too I believe
and doing anything to smooth out the air flow.

Extreme ideas are removing mirrors putting a tapered cone on the back lowering the car and chopping the top. closing the bottom of the car with flat panels will increase down force but also smooth out any of the air flow under the car.
wheel well covers so that the air will flow around the wheels like the have on honda

mechanically lowering the final drive ratio of your car is probably the easiest way to improve gas mileage the f40 trans out of the G6 has a final drive in 6th gear of 0.62 and there are a could of posts where i have seen people getting 1900 rpms at 70 mph I have the 3spd auto and when working correctly i get 24 mph I would love to get this trans since before the tach went bad I was at 5000 plus rpms at 65-70 and the 125 trans a final drive ratio of 1:1

The main thing to affect your gas mileage is free with a cost in some time is your driving habits and who says you have to drive at 70 drive 65 or 60 and show off that fiero :-)

correction http://www.fastfieros.com/N...nsmission_ratios.htm

20005-06 G6 6 Speed MT2/F40 3.55 3.77 2.04 1.32 .95 .76 .62 --
6200 RPM 34 64 99 137 171 180+
7000 RPM 41 70 104 153 180+ 200+ --

Gas Mileage Speed
1925@65

[This message has been edited by hawkebat (edited 03-13-2012).]

What are you trying to achieve? Better MPG? If so, then there are other things you can do. What you spend on body mods may never be seen in fuel savings, moneywise.

Want better MPG? Drive slower. Fieros were built for 55MPH speed limits. They are geared for this.

quote Originally posted by hawkebat: mechanically lowering the final drive ratio of your car is probably the easiest way to improve gas mileage the f40 trans out of the G6 has a final drive in 7th gear of 0.52 and there are a could of posts where i have seen people getting 1900 rpms at 70 mph

The F40 trans is a 6 speed manual, not 7, and the top gear is 0.62:1 (MT2) or 0.71:1 (MU9), depending on which year trans it is. The FD ratio is 3.55:1, so you'll either have 2.21:1 (MT2) or 2.52:1 (MU9), for the ratio at the axles.

But either way, at 75MPH, in a totally stock 87 GT, if it's a 5 speed Getrag trans, you should be getting 28-30 MPG on the highway.

i was getting around 30 with my 2.8 before it started limping along. i wonder what the 3.4 will get? oh wait i dont care, my gf has a duke that gets almost 40 highway... bahaha

I had no idea the rear wing reduces drag. I knew it helped stabilize the car, and as such is one of the few wings/spoilers that's actually functional on mass produced cars. Not to mention it looks incredibly cool. (especially on an aero-notchback)

quote Originally posted by Austrian Import: I had no idea the rear wing reduces drag. I knew it helped stabilize the car, and as such is one of the few wings/spoilers that's actually functional on mass produced cars. Not to mention it looks incredibly cool. (especially on an aero-notchback)

I don't get why anyone would say a spoiler/wing on any car is "non-functional" unless it was inside the passenger cabin. All spoilers/wings on all mass production cars are functional, even if they are only put their for looks. Their primary function in that case may not help with fuel economy or performance, and may even hinder it, but they are still functional. Just because it's not performing a useful function, doesn't mean it isn't functional.

You will spend way more money modifying the car then you will save in gas. If you really want to increase the mileage reduce the speed. Not only were Fiero’s geared for 55 MPH but more importantly there are some basic physics working against you. In simple terms, to get a 10% increase in speed you need a 30% increase in power. This is with everything else being equal (no change in the car’s drag or rolling friction). Unfortunately what it takes to get a significant reduction in drag (enough to see a noticeable difference) means some major changes. 75 MPH is a 36% increase in speed which means you need a 108% increase in power. Fortunately that doesn’t equate to a 108% increase in fuel (the equation to figure that out it beyond me) but it’s not small either.

I find the most valuable function of the spoiler on my car is that it sometimes blocks the headlights of the HID-hero behind me. Which is good enough, but other than that it's just 10lbs of dead weight. If it made any real improvement in gas mileage it would have been standard equipment. If it made any real detriment to gas mileage, it would have been designed differently to not do that.

[This message has been edited by armos (edited 03-14-2012).]

For anyone saying "slow down, the Fiero was designed for 55MPH limits" you might as well just say "don't drive your car."

Sure, driving 55 on the highway will get you a few more MPG, but also put you at a greater risk for being in a wreck, or having someone develop road rage because of you; putting not only yourself in danger, but others on the road with you as well. Driving 55 on a highway where the speed limit is anywhere between 65 and 80, is just asking for trouble. Most people drive anywhere between 5-15 MPH over the limit. On a 70 MPH limit stretch of highway, that puts an average of 25 MPH difference between you, and everyone else on the road with you, including the tractor trailers.

If I can get 28 MPG in a stock 87 GT 5 speed, driving 900 miles through monsoon and mountains, at 75 MPH almost the entire way, then so can you. If you've got the 3 speed auto, well, sucks to be you. Swap it out for a 4 speed auto, or a stick, and get an overdrive gear or two.

Whatever you do, don't drive too slowly, or too fast, on the highway. Maintain safe speed and distance relative to the other cars around you.

For what it's worth, on http://fueleconomy.gov/ an 87 Fiero w/2.8 5 speed is rated at 26 MPG highway. And it lists "user's average" as 27.6 MPG. So don't listen to the "55 MPH" crowd. You should be getting at least that, at 70-75 MPH on the highway. The automatic is a little lower.

quote Originally posted by dobey: For anyone saying "slow down, the Fiero was designed for 55MPH limits" you might as well just say "don't drive your car." Sure, driving 55 on the highway will get you a few more MPG, but also put you at a greater risk for being in a wreck, or having someone develop road rage because of you; putting not only yourself in danger, but others on the road with you as well. Driving 55 on a highway where the speed limit is anywhere between 65 and 80, is just asking for trouble. Most people drive anywhere between 5-15 MPH over the limit. On a 70 MPH limit stretch of highway, that puts an average of 25 MPH difference between you, and everyone else on the road with you, including the tractor trailers. If I can get 28 MPG in a stock 87 GT 5 speed, driving 900 miles through monsoon and mountains, at 75 MPH almost the entire way, then so can you. If you've got the 3 speed auto, well, sucks to be you. Swap it out for a 4 speed auto, or a stick, and get an overdrive gear or two. Whatever you do, don't drive too slowly, or too fast, on the highway. Maintain safe speed and distance relative to the other cars around you. For what it's worth, on http://fueleconomy.gov/ an 87 Fiero w/2.8 5 speed is rated at 26 MPG highway. And it lists "user's average" as 27.6 MPG. So don't listen to the "55 MPH" crowd. You should be getting at least that, at 70-75 MPH on the highway. The automatic is a little lower.

My point was that the car was build for 55MPH. EPA ratings are for 55MPH highway. Going faster will reduce MPH. If you want better gas mileage, then slow down. If you have to drive faster because of traffic, then do so. Here, I can drive 70MPH all day and not be bothered with faster or slower cars. But my highway is not congested.

quote Originally posted by dobey: If I can get 28 MPG in a stock 87 GT 5 speed, driving 900 miles through monsoon and mountains, at 75 MPH almost the entire way, then so can you. If you've got the 3 speed auto, well, sucks to be you. Swap it out for a 4 speed auto, or a stick, and get an overdrive gear or two.

I pulled out 26 MPG with the 3 spd in my 88 on a trip back from the Dells Run. This was at an average of 70 MPH. Steady speeds are more important than the difference between 70 and 55 MPH...

While all these things are true, the question was how to reduce the drag coefficient. I do agree lowering the c/d on a Fiero will have a minimal effect on economy at highway speeds and there are other ways to provide a more signifigant fuel economy gain. Honestly lowering the drag would only really be beneficial at higher speeds or if you intend to do some LSR type racing, but most of the mods[besides chopping the top] are relatively easy and or cheap to pull off in comparison to an engine swap.......

...........hmmm, an LSR Fiero sounds like a fun project, I thought about building one awhile back but ran out of funds/time. It would be interesting to see just how fast a Fiero could be pushed

the most noticeable gains you can find in MPG's would be to lower the car and add a rear hatch.

V8 Archie - http://www.v8archie.com/v8Archie/Kit5.htm
Fiero Fiberglass - http://fierofiberglass.com/...Pages/Hatchback.html


my friend has 2 DeLoreans. and when he removed the rear louvers he noticed a 4-6 mpg loss on the freeway during a journey from Pewaukee, WI to St.Cloud, MN

so as the rear end of both cars are fastback's it would stand to prove that adding rear louvers or a hatch would gain a fiero better freeway MPG's as well.

also - if you add the rear hatch dont's have the spoiler as it will cause slight drag to the airflow you have gained.

you want the body to be as "streamlined" as possible.

don't have scoops, spoilers, or anything that would create an obstruction.

also, it you know how to weld or fabricate.

you can add windage trays under the front and rear of the car to lessen the drag going under the body.
another thing to do is remove excess weight (but that's a hole different subject)

quote Originally posted by jaskispyder: My point was that the car was build for 55MPH. EPA ratings are for 55MPH highway. Going faster will reduce MPH. If you want better gas mileage, then slow down. If you have to drive faster because of traffic, then do so. Here, I can drive 70MPH all day and not be bothered with faster or slower cars. But my highway is not congested.

EPA ratings are not for 55 MPH highway. The were 55 MPH on a closed oval track. Fill tank, drive around track until empty, calculate MPG. Now it is 65 MPH. The ratings on fueleconomy.gov are all adjusted for newer standards. Also, the observed ratings are almost certainly from people exceeding the speed limit; not people who are driving 55 MPH to save on gas. So that rating for the Fiero on fueleconomy.gov most likely used to be higher, until they applied some math to adjust it. The difference in fuel economy between driving 55 MPH and 70 MPH on the highway, in a Fiero, is completely negligible. You won't see any meaningful improvement in it.

quote Originally posted by carbon: I pulled out 26 MPG with the 3 spd in my 88 on a trip back from the Dells Run. This was at an average of 70 MPH. Steady loads are more important than the difference between 70 and 55 MPH...

Fixed If you drive at a constant speed, you're always varying the engine load... sometimes coasting, sometimes heavy throttle. This kills gas mileage. If you keep the engine load even - typically where you don't need a lot of pedal to keep a specific speed - then you will see MPG improvements. If you have to slow down a few mph to gain 5mpg, then so be it. A vacuum gauge can work wonders here, the more vacuum you pull at a given speed will net better mpg because fuel atomizes better.

quote Originally posted by av8fiero: While all these things are true, the question was how to reduce the drag coefficient.

Actually, the question was "how do I get more MPG?" while the reference to lowering the c/d was an implied best means to do so. And it isn't, on a Fiero at least.

If you want to waste a lot of money, on a very minor improvement, though, it's a great way to empty your wallet. I have a magnet you can put on your fuel line too, that realigns the atoms in the fuel so you use less of it. Only $9.99!

quote Originally posted by dobey: The difference in fuel economy between driving 55 MPH and 70 MPH on the highway, in a Fiero, is completely negligible. You won't see any meaningful improvement in it.

Based on what test? I have seen a difference when driving 55 vs 70 on my '84.
BTW, I have to say that EPA MPG is a joke. They need real world info. My new HHR doesn't get what the EPA says, but yet it is on the sticker. Others have said the same thing. How about real test results for that model of car??? sad.

quote Originally posted by jaskispyder: Based on what test? I have seen a difference when driving 55 vs 70 on my '84. BTW, I have to say that EPA MPG is a joke. They need real world info. My new HHR doesn't get what the EPA says, but yet it is on the sticker. Others have said the same thing. How about real test results for that model of car??? sad.

Based on the gearing of an 87 GT 5 speed and the c/d of the Fiero. What gearing is in your 84? What difference were you seeing?
I think the EPA ratings have gotten much better. I don't know about the HHR, but I know my Cruze Eco does get 42 MPG on the highway. In fact, I am certain I can get at least 45 MPG out of it, if not more. One of my two lengthy trips with it saw some fairly heavy traffic, and people slowing down for no apparent reason, which sort of killed the average a bit. The other was through the mountains.

Anyway, the OP is not likely to see any useful gain in MPG by dropping to 55 MPH from 70-75. Also, the Fiero GT was not "designed to go 55 MPH" just because the limit was 55 in the 80s. It was designed to get the most performance out of the second-hand parts bin at GM, while still letting them sell it as a "sporty economy commuter car." Also, even with the oil issues of the 70s, gasoline was still incredibly cheap at the time, and "fuel economy" wasn't the biggest concern of any of the car makers at the time. GM was still recovering from all the hits to performance their cars took in the 70s, and trying to bring back the power and performance mantra to their lineup.

quote Originally posted by dobey: Based on the gearing of an 87 GT 5 speed and the c/d of the Fiero. What gearing is in your 84? What difference were you seeing? I think the EPA ratings have gotten much better. I don't know about the HHR, but I know my Cruze Eco does get 42 MPG on the highway. In fact, I am certain I can get at least 45 MPG out of it, if not more. One of my two lengthy trips with it saw some fairly heavy traffic, and people slowing down for no apparent reason, which sort of killed the average a bit. The other was through the mountains. Anyway, the OP is not likely to see any useful gain in MPG by dropping to 55 MPH from 70-75. Also, the Fiero GT was not "designed to go 55 MPH" just because the limit was 55 in the 80s. It was designed to get the most performance out of the second-hand parts bin at GM, while still letting them sell it as a "sporty economy commuter car." Also, even with the oil issues of the 70s, gasoline was still incredibly cheap at the time, and "fuel economy" wasn't the biggest concern of any of the car makers at the time. GM was still recovering from all the hits to performance their cars took in the 70s, and trying to bring back the power and performance mantra to their lineup.

HHR gets about 2MPG less than EPA states it should and this is consistent when I calculate it out.

True, the Fiero is a parts bin car, but it was geared for 55MPH as was the tranny and the engine RPM. Sure, it can go higher, but it is really optimized for the limitations at that time. Gas didn't get cheap/plentiful until after the end of the Fiero.... so MPG was still an important issue.

BTW, my 84 had the 4:10 tranny. Great for stop and go, not so good for highway.

First off ecomodder.com is a great website thanks for that.
And now i have been thinking about drag coefficients how stable is this car at higher speeds and how to make it more stable than it is now?

quote Originally posted by Shonyman32: First off ecomodder.com is a great website thanks for that. And now i have been thinking about drag coefficients how stable is this car at higher speeds and how to make it more stable than it is now?

The biggest single improvement you can make is a hood vent. I make those in three different styles (shameless plug ). I also make fender vents & headlight covers with vents. All of which will reduce the front end lift you get at speed due to the air flowing through the radiator being routed under the car.
~ Paul
aka "Tha Driver"

Custom Fiberglass Parts

quote Originally posted by gtxbullet: ....add a rear hatch. V8 Archie - http://www.v8archie.com/v8Archie/Kit5.htm

Jesus H, that's sweet! Think I just added something on my "To Do" list...

Thanks for the share!

I don’t recall anybody saying you should just slow down but rather if you want to increase the fuel economy slowing down is the best way to do it. Yes you could find ways to reduce the drag and/or increase the engine performance (increased performance can actually increase mileage) but the savings versus the cost don’t add up. As to “don’t drive to slow” I do agree however I don’t agree that you should “go with the flow” just to keep others happy if the “flow” is going 80mph in a 60mph zone. The number one cause of freeway collisions is inattentive driving (not paying attention). The stopping distance between 60mph and 80mph is 60% longer and I can’t justify it by “not wanting to piss someone off”.

quote Originally posted by Shonyman32: First off ecomodder.com is a great website thanks for that. And now i have been thinking about drag coefficients how stable is this car at higher speeds and how to make it more stable than it is now?

What is "higher speeds" exactly?

(At a legal place to do this btw) But top speed stabilization

I agree that ecomodder.com is a good place to get info on saving fuel. But like most other web forums, they tend to be somewhat clique-ish. For example, they've decided that an old aero template from the 1930s (or something like that) is the end-all be-all of aerodynamics.

But anyway...

One of the most effective fuel efficiency mods is to mod the driver. I'm referring to adjusting your driving style. It doesn't matter how wonderfully efficient your car is, if you drive like a **** . Because all that wonderful efficiency will go right out the window. Yes, modding the car does help. But IMO you should start with the driver.

Best of luck!

quote Originally posted by Shonyman32: (At a legal place to do this btw) But top speed stabilization

If you add a hood vent or vents inside the front area under the hood, to keep the headlight doors down at speed, and everything is well maintained, the stock V6 Fiero is fine at the 120 MPH the speedo goes to.