I'd love to see some ideas on how to eliminate the two rear deck vents. I've seen some styling approaches such as custom design replacements/covers and the overhead scoops. These are of no interest to me.
Obviously, ventilation needs to be maintained, and I've seen numerous "reverse scoops" that appear to aid this intent. (But I'm not so sure the deck vents were additionally removed.) And I'd rather not hinder rear vision with a setup as some of the rear facing scoops do.
I'm not sure, but I think the reason they got rid of the vents in the middle of the deck lid was because it caused water to run down into the front plugs, and also onto the front exhaust manifold, which would cause it to crack from the temperature change.
With a front engine car, a lot of the air that passes through the grill and radiator also passes over the engine to cool it. With the engine in the rear, you don't get that natural airflow so you get a much hotter engine compartment. In addition, there isn't a lot of room in the V6 models, so all the heat coming off the engine doesn't really have anywhere to go. I've seen some really nice setups where there has been a rear facing scoop complete with fan that in theory would go a good job of drawing out the warm air, and eliminate water getting in.
Air in a "normal" front-engined vehicle travels through the "front" of the car - whether it be through the front grill or lower valiance, whatever the car has - and travels around and then escapes back underneath the car under the firewall. Back in the day, some tuners found out that you could raise the "rear" of the hood (as in the part that's near the windshield) and create another exit path without the need to install a hood scoop. Some in the Japanese tuner scene have taken this same concept and applied it to their cars even today.
For mid-engined vehicles like the Fiero, air enters the front of the vehicle, but travels along the underside of the car and then escapes through the topside of the decklid through the engine compartment. This is the reason why mid-engine and rear-engine vehicles have to have relatively flat bottoms - to ensure air follows that path to go up through the rear of the car. With the gas tank, not only was it put directly in the middle of the car to give an ideal weight balance but it was also put there to "flatten" out the bottom of the chassis. Up front the Fiero retains an opening on the bottom strictly for the purpose of allowing air to enter the radiator area. If the Fiero did not have a front radiator then there would be no need for it to have openings anywhere on the front.
When GM created the 1984 model Fiero, the large magnesium center decklid vent was an ideal means by which for this air to travel as it traveled nearly straight out the middle of the vehicle. However the big issue with the 1984 center decklid vent cars is that so much debris gets into the car that it caused a lot of issues; one of which being an attribution to the 1984 engine fires. For 1985 the side service panels (they're even referred to as this in some 1984-era Fiero manuals) were changed to be the air escape vents.
You can eliminate the stock decklid vents, whether you have a 1984 car or later model Fiero. However there still needs to be some sort of means by which to have air escape - it just has to. If you completely seal off the rear engine compartment (if you can even find a way to do that, as residual air will still make it's way through crevices in the rear of the car), you will run the risk of causing your car to have a much lower point to where it will begin to overheat (i.e., it'll overheat faster).
The air traveling under the car and exiting through the top-side of the rear of the Fiero is not some kind of sorcery. Forum members have ran their own tests over the years to show how air flows both under and over the Fiero.
[This message has been edited by Fiero84Freak (edited 11-24-2013).]
I ended up molding in the center vent from and 84 to my GT decklid. The vehicle is in a garage so I don't really worry about rain damaging the plugs and exhaust headers. I think this would be the only safe way other than a decklid scoop to remove the vents.
Where does all that air in front engine compartment go then?
It passes out underneath the car. You have air entering at a higher point through a vertical radiator and passing over the entire area of the engine. The firewall is usually tilted somewhat from top to bottom just as the front wall of the Fiero's front storage compartment and without a transmission driveline in the way, the air can pass underneath.
On the Fiero, the air enters the engine compartment in part due to being scooped up by parts of the vehicle, and also because the air is compressed under the flat pan of the car and quickly expands as it hits the open area of the engine bay. The vent grills above act as a vacuum, being a lower pressure area than the area at the bottom of the engine bay. Volkswagen Beetles and Indy race cars use this principal.
Years ago, someone here did some air flow testing on the rear deck of a Fiero. I did some of my own, but at the time didn't have a camera to record it and could only tell what was happening by looking back until I felt I was leaving the roadway. I taped small strips of surveyor's marker tape onto the deck lid in rows, front to rear and side to side, evenly spaced at about 6 inches apart. Driving down the road, you would be surprised at how many of them are actually blowing toward the rear window of the car. This method might help you to decide if you want to install something like a reverse hood scoop into the deck lid, and where you would want the opening to be.
On my kit car, I used household gutter downspout attached to the bottom of the VW pan to collect air up near the front wheel area, carry it back to the front of the engine bay and with the elbows that attach a downspout to the gutter, it was directed up toward the engine intake fan. It really cooled the engine down. Because of the ground effects on the car, they weren't visible without looking underneath the car. They're actually installed but not visible as it sits in this picture.
I grabbed a set of 'solid' covers from an '84, & installed a mustang scoop. The decklid was replaced (by request) at the Fiero Factory, & I've been running with a stock notchback decklid & still using the 'solid' covers. I never cared for the look of the later ones. Once the fastback conversion is done, I'll re-cut & apply the mustang scoop on the decklid.
Open the front cover on your Fiero and look at the way the the seals for the trunk leave a channel to let some air air flow along the sides of the cover and then the two rubber pieces near the windshield wipers push the air way from the opening that lets air into the cabin. That was designed so not all of the air would push out under the car, and maybe to give some down force to the nose of the car. Look at the rear of the car and you can see the same thing to vent some air out of the engine compartment.
Some sort of rear diffuser below the tail lights? Probably have to cut out the lower part of the trunk but if the air wasn't allowed to exit via the decklid vents, it would eventually be forced into the diffuser duct work...right?
Hot air rises...thats why the vents are at the top of the engine compartment. If you put vents down lower, it would just draw more air in and still no place to go. A rear diffuser would be totally worthless except for cosmetics...if you like that. Front engine cars, like already described pull air in thru the radiator and also in at the front under the bottom. It goes thru the compartment and most is directed down and out of the car by the firewall, which is why in most cases the firewall is sloped down and towards the back at the bottom. Its to 'funnel' the air down and out. If you look at Ferraris like the 308/328/355, you will see the whole decklid is mostly all louvers. as yours is now, you still have to worry somewhat about water getting thru onto the engine. Its not going to be in the garage for the rest of its life. Your going to get caught in rain at some point, or simply washing it will pour water onto the engine.
OK thanks for responses. Here's a thought (feeding the "fire" so-to-speak):
A number of responders have mentioned how the firewall in front engine cars have a slope to direct exiting air under the car. When I look at the forward wall of the rear trunk in the Fiero, that too has a sloping section (bottom half) near the muffler.
It's likely though that it doesn't quite function in the same manner. I can imagine air getting trapped at the upper half of the trunk wall.
It wont be trapped because it flows out the vents....
Im sure the slope on a Fiero is just for convenience to give space for components. That firewall space is behind the seat so its not useful to the interior, so its just handy to make more space for the engine bay.
Is yours a notchie or fastback? I drive a fastback but actually prefer the look of the notchies, however I like the fastback vents more because of the way they are curved on the outsides. If I had my way, which I might some time in the future, I'd have a "shorty" fastback with GT vents and a notchie decklid and tail lights.
[This message has been edited by Boostdreamer (edited 11-27-2013).]
I'll stir the pot one time: Looking to get some more ideas if you would? (I really dislike those vents )
Start with a hood vent on the front. If you want to get rid of the top vents on the rear, you need a top vent in the front, to get rid of the hot air off the radiator before it flows under the car to the rear. Then maybe plate up the bottom of the car to smooth it out and make it more flat behind the radiator, and before the engine bay. That should help get a lot of hot air out the front, and help the cooler air flowing underneath, flow faster with less turbulence. Additional flow work with a good diffuser at the rear bumper, might help to create a vacuum underneath, and suck the hot air out the back and underneath the car, rather than out of the top. A reverse mustang scoop, or molding in the 84 scoop or similar to the decklid wouldn't be a bad idea though.
That won't get you a proper finished product, but it's a start. If you want to do it right, you need to hire a couple aerospace engineers or similar, and spend some time in a wind tunnel, though.
Also, our pilot-type members should be familiar with the Bornoulli effect as it applies to the Fiero's aerodynamics. In principal, it says that faster moving air has lower pressure. That's why the top surface of an aircraft wing is curved while the underside has a somewhat flatter surface. Large volumes of air taken in at the front of the Fiero and forced down underneath into the small space between the belly pan and ground helps to hold the car to the ground because it moves much faster to reach a point that it can equalize with atmospheric pressure. That point is the engine bay. As the air reaches that point, it quickly expands into the engine compartment. A venturi effect in the area of the rear window helps to pull the air from the engine bay and exhaust it through the vents. Moving vents to the rear of the car might hamper this if it were in a high pressure area.
I really like the front of the black one above. Nice work and no mistaking it for anything other than a Pontiac.
I wouldnt be moving vents around. Designers with millions of dollars in resources figured all this out before the car was ever manufactured, then tweeked as production went on. Just throwing things at it for improvements without the knowlege and testing is unproductive. Its like putting an 1100 cfm carb on a 2.2. JMO.