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Fiero hump on the trunk by 85fieroguy
Started on: 08-27-2015 09:04 PM
Replies: 25 (627 views)
Last post by: fierofool on 09-01-2015 06:02 PM
85fieroguy
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Report this Post08-27-2015 09:04 PM Click Here to See the Profile for 85fieroguySend a Private Message to 85fieroguyEdit/Delete MessageReply w/QuoteDirect Link to This Post
After having a flat trunk surface, why did Pontiac go to a " hump" ??? As for heat ventilation, I thought the extra middle vent, besides the 2 side vents was a good idea, so why did they change the design ?? ..... more room for a supercharger???
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Report this Post08-27-2015 09:24 PM Click Here to See the Profile for FieroMontrealClick Here to Email FieroMontrealSend a Private Message to FieroMontrealEdit/Delete MessageReply w/QuoteDirect Link to This Post
No v6 in 84, they needed more clearance for the 2.8l in 85

------------------

AKA. FieroAlex

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fierofool
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Report this Post08-27-2015 09:25 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
In brief, it was for clearance of the V6 engine, introduced in 85, rather than continuing to produce two different deck lids.

Ditto! What /\ he said

[This message has been edited by fierofool (edited 08-27-2015).]

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Khw
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Report this Post08-27-2015 09:45 PM Click Here to See the Profile for KhwClick Here to Email KhwSend a Private Message to KhwEdit/Delete MessageReply w/QuoteDirect Link to This Post
And the middle vent wasn't "extra". The cars equipped with the middle vent had solid side covers. When they switched to the lid with a hump they moved the vents out to the side. Some people will get vented sides and put them on a car equipped with a middle vent for more ventilation, but they didn't come that way stock as far as I can recall.
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85fieroguy
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Report this Post08-27-2015 09:51 PM Click Here to See the Profile for 85fieroguySend a Private Message to 85fieroguyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Wish I didn't repaint my trunk with the high spoiler, would have preferred the " old style trunk" and have 3 vents. The heat from the V-6 is no joke, I'm surprised that besides coils, more parts don't burn out.
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Report this Post08-27-2015 09:57 PM Click Here to See the Profile for solotwoSend a Private Message to solotwoEdit/Delete MessageReply w/QuoteDirect Link to This Post


 
quote
Originally posted by Khw:

And the middle vent wasn't "extra". The cars equipped with the middle vent had solid side covers. When they switched to the lid with a hump they moved the vents out to the side. Some people will get vented sides and put them on a car equipped with a middle vent for more ventilation, but they didn't come that way stock as far as I can recall.


Hmmm I wonder if an 84 deck lid would work with the 3800SC. Sure could use some relief from the heat that engine produces.
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85fieroguy
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Report this Post08-27-2015 10:11 PM Click Here to See the Profile for 85fieroguySend a Private Message to 85fieroguyEdit/Delete MessageReply w/QuoteDirect Link to This Post
If the 84 deck lid works, let me know. If its good for a 3800, it should be good for a V-6. 3 vents will be better then 2.
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dobey
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Report this Post08-28-2015 09:33 AM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 85fieroguy:

If the 84 deck lid works, let me know. If its good for a 3800, it should be good for a V-6. 3 vents will be better then 2.


Except for when cold water falls through the middle vent and cracks the exhaust.

The two side vents are more than enough. What would help more, would be to add ventilation in the front, so that heat pulled off the radiator flows up and over the car, or out to the sides, rather than under the car.
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Report this Post08-28-2015 09:35 AM Click Here to See the Profile for HorseSend a Private Message to HorseEdit/Delete MessageReply w/QuoteDirect Link to This Post
The magnesium center vent was removed after the 84 model because leaves would fall though land on top of the scorching hot catalytic converter and caused fires. The solid magnesium side covers were removed because once the leaves or debris caught fire the fire would set the magnesium on fire and it was next to impossible to put the fire out. Water will not put out a magnesium fire. The 84 Fiero suffered from bad connecting rods that often failed and broke though the block, the motor oil would spill on the scorching hot catalytic converter causing a fire, again the magnesium center vent would catch fire. This had nothing to do with the removal of the center vent just the removal of all magnesium parts as water will not put out a magnesium fire. The revised deck lid still trapped some leaves because of the seal, the leaves would collect in that area and dry causing a smaller risk of fire when the deck lid was opened as the now dry leaves could fall onto the catalytic converter so a recall was initiated to cut the strip. A center vent will cause a higher risk of fire due to the high temperatures of engine components so it was removed and replace with aluminum side vents, these vents will melt in a fire but not ignite.
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Glen87
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Report this Post08-28-2015 09:55 AM Click Here to See the Profile for Glen87Send a Private Message to Glen87Edit/Delete MessageReply w/QuoteDirect Link to This Post
Interesting info Horse, and the points you bring up make a lot of sense.

As for the earlier poster asking whether or the the 84 deck lid will work with the 3800sc, it will work. My 84 has that swap done on it and while I like the big open vent for cooling purposes I hate the fact that water can get down in there and sit on my lower intake manifold. Also I do get a lot of leaves in there and hate it. They do the same thing, sit on the LIM.
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85fieroguy
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Report this Post08-28-2015 01:23 PM Click Here to See the Profile for 85fieroguySend a Private Message to 85fieroguyEdit/Delete MessageReply w/QuoteDirect Link to This Post
So...I assume a 84 flat trunk lid with a center vent WILL NOT fit over a 85GT with a V-6 . True ???
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Report this Post08-28-2015 03:35 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 85fieroguy:

So...I assume a 84 flat trunk lid with a center vent WILL NOT fit over a 85GT with a V-6 . True ???


If a 3800 SC will fit, then the 2.8 will fit. You will get leaves and water flowing directly onto the engine and exhaust if you do, though.

The "hump" is not for clearance.
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Khw
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Report this Post08-28-2015 07:54 PM Click Here to See the Profile for KhwClick Here to Email KhwSend a Private Message to KhwEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by dobey:


If a 3800 SC will fit, then the 2.8 will fit. You will get leaves and water flowing directly onto the engine and exhaust if you do, though.

The "hump" is not for clearance.


Yeah, I think it was Skitime or something like that who cut the hump out and put a plexiglass panel in it's place. The plexi was flat and he had the V6.

[This message has been edited by Khw (edited 08-28-2015).]

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fierofool
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Report this Post08-28-2015 08:06 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Obviously the 84 decklid and grill would be a bigger problem with water and debris because of the front bank of the V6 motor sitting so far forward. I've never looked at the construction of the 84 decklid, but it's been posted so many times on this forum that the design of the 84 lid creates clearance problems with the forward area of the intake and throttle body.

I've also seen some of the glass inserts but they were located in the area of the center panel and flush with the top of the decklid. That center panel is well above the reinforcing ribs that surround it. There would be an obvious difference in the location of the reinforcing ribs of the 84 and later decklids, just due to the big center grill. Does the 3800 NA sit lower than the 2.8? I know that there can be some clearance problems with the 3800SC and sometimes requires relieving an area of the right side reinforcing rib around the flat panel where the glass is usually located.
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Report this Post08-28-2015 09:37 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Khw:
Yeah, I think it was Skitime or something like that who cut the hump out and put a plexiglass panel in it's place. The plexi was flat and he had the V6.


The fastback deck lid doesn't have the hump anyway.
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dratts
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Report this Post08-28-2015 10:16 PM Click Here to See the Profile for drattsClick Here to Email drattsSend a Private Message to drattsEdit/Delete MessageReply w/QuoteDirect Link to This Post
I thought that the trunk was in front. Would that be a hood?
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Report this Post08-28-2015 10:26 PM Click Here to See the Profile for KhwClick Here to Email KhwSend a Private Message to KhwEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by dobey:


The fastback deck lid doesn't have the hump anyway.


Gah! I was thinking so much about the notchback deck lids that my mind just glossed right over that part.
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fierofool
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Report this Post08-28-2015 11:57 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by dobey:


The fastback deck lid doesn't have the hump anyway.


No, it doesn't. But the notchback decklid is flat at the front edge with the hump giving it elevation. The fastback decklid rises sharply for a height of maybe 3 or 4 inches from it's front edge, giving the whole decklid a higher elevation comparable to the notchback hump.
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dobey
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Report this Post08-29-2015 07:37 AM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by dratts:

I thought that the trunk was in front. Would that be a hood?


The trunk is aft of the engine bay. The front is spare tire well.
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Report this Post08-29-2015 07:59 AM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fierofool:
No, it doesn't. But the notchback decklid is flat at the front edge with the hump giving it elevation. The fastback decklid rises sharply for a height of maybe 3 or 4 inches from it's front edge, giving the whole decklid a higher elevation comparable to the notchback hump.


My point was that using skitime's clear glass mod as a comparison for "what will clear" isn't valid, because there is no hump to remove. The fastback lid is already flat.

The hump is obviously not for clearance though. The bottom side of the decklid is still flat on the notchback cars. There's no additional hump area underneath. Clearance was made underneath by altering the location of the support rib. This support beam going across the decklid is clearly the most probable interference point for the V6, though I don't think the V6 is really any taller than the air cleaner housing on the duke. The V6 would clearly be an impediment to air flow at the central vent though, being wider, and having a large flat intake.

My best guess as to why the hump is there, would be as an aerodynamic feature, to induce turbulence with the lack of the central vent, which would have induced turbulence in the middle prior, as a means to help keep the rear glass cleaner and provide a clearer view through the rear view mirror. There's basically no other sensible reason for the exterior hump to exist.
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fierofool
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Report this Post08-29-2015 10:16 AM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Agreed the fastback decklid is somewhat flat even though it has a slightly raised center portion. Looking at the underneath of the notchback and fastback decklids shows that the underside of the notchback has shallower ribs where the hinges mount and the recessed area is curved upward from the mounting ribs. It isn't as flat as the fastback lid. The fastback ribs are deeper, thus elevating the surface of the decklid, reducing the need for the hump. Add to that, the front edge of the notchback is on the same plane as the majority of the decklid while there is a 45 degree lip on the fastback lid, which assuming that the front edge where the recall strip is located is at the same level, then the surface of the fastback would be higher.

I placed a straight edge at the ends of the hinges where they mount to the decklid. Measuring upward to the center surface of the notchback and fastback decklids, I got a 5/8 inch difference in depth of the pocket where the metal plate is mounted. The hump may not have been for clearance, but there's certainly a difference in clearance of the notchback and fastback decklids.

Just now, I don't have time to find a point on the chassis to measure the height of the motor compared to decklid, comparing notchback and fastback. After weekend family activities are over, maybe we could continue our discussion. We might not settle the reason for the hump, but we may be able to determine if there's a difference in clearance. Add our findings to the list of Fiero Trivia.
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Report this Post08-29-2015 12:54 PM Click Here to See the Profile for bjc 350Send a Private Message to bjc 350Edit/Delete MessageReply w/QuoteDirect Link to This Post
My 84 with the 3.8sc motor uses the center vent with two vented side covers rather than the original solid ones. It works well, but I seldom get caught in the rain or let the car sit out to gather any leaves or trash. However, at the height my motor sits, the left reinforcing rib had to be notched and reinforced in the area where the throttle body and associated goodies reside. After reinforcing the notch, the hood would not fit flush on the left side. I found that the torsion bars that hold the trunk up where exerting enough pressure to twist the trunk/engine cover. I took out the torsion bars and installed a Dickman hydraulic strut kit and that let the trunk settle into the correct position. For an everday driver, I,m not sure the fully vented lid would be the way to go. It does look like a lot of water could get in and cause problems. The car has no overheating problems and the trunk doesn't get too hot.

poor lid fit


fully vented lid- only picture I have.

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85fieroguy
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Report this Post08-29-2015 02:52 PM Click Here to See the Profile for 85fieroguySend a Private Message to 85fieroguyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Nice write up...your car gives me an orgasm !!!! Thanks for the info..gonna get a good, white 84 trunk lid and center vent for a spare. Only drive my 85GT when its nice out.
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fierofool
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Report this Post09-01-2015 03:03 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
This morning I pulled the 86SE and the 87GT alongside one another and took a few measurements and made some observations.

Using a straight edge at the center of the top, the bottom edge flush against the seam between the front and rear sections of the roof, I measured to the top of the deck lid at the center of it's width. The Fastback measured 10 3/8 inches to the top surface of the decklid at the center of it's width. The Notchback measured 10 1/2 inches at the same point. Difference in surface height could be due to a few variables, so I'll assume the top surface is equal on both models.

Next, I looked underneath and I saw some difference in the underside construction. The Fastback hinge mounting ribs are deeper than those of the Notchback. But then looking a little closer, this creates the illusion that the Fastback lid has more clearance underneath. Not true. The Notchback's inner decklid shell actually slopes upward from the hinge mounting ribs to a point then levels out in the area where the metal plate is mounted. The Fastback is practically flat all the way across. The fastback also appears to be without a hump when viewed from the outside, but that's because the sides beyond the center hump have been raised about 2 inches to almost the same height as the Notchback hump. That would account for the 45 degree rise across the width of the front of the Fastback decklid.

If there is any area on the 84 decklid that might be of concern, clearance wise, would be the rib running side to side along the area where the metal plates are attached to the fibereglass portion of the lid.
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Report this Post09-01-2015 03:22 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fierofool:

This morning I pulled the 86SE and the 87GT alongside one another and took a few measurements and made some observations.

Using a straight edge at the center of the top, the bottom edge flush against the seam between the front and rear sections of the roof, I measured to the top of the deck lid at the center of it's width. The Fastback measured 10 3/8 inches to the top surface of the decklid at the center of it's width. The Notchback measured 10 1/2 inches at the same point. Difference in surface height could be due to a few variables, so I'll assume the top surface is equal on both models.

Next, I looked underneath and I saw some difference in the underside construction. The Fastback hinge mounting ribs are deeper than those of the Notchback. But then looking a little closer, this creates the illusion that the Fastback lid has more clearance underneath. Not true. The Notchback's inner decklid shell actually slopes upward from the hinge mounting ribs to a point then levels out in the area where the metal plate is mounted. The Fastback is practically flat all the way across. The fastback also appears to be without a hump when viewed from the outside, but that's because the sides beyond the center hump have been raised about 2 inches to almost the same height as the Notchback hump. That would account for the 45 degree rise across the width of the front of the Fastback decklid.

If there is any area on the 84 decklid that might be of concern, clearance wise, would be the rib running side to side along the area where the metal plates are attached to the fibereglass portion of the lid.


It seems that generally, the support beams that provide any clearance issues, are the two which mount to the hinge, on any model Fiero. These are the ones that need to be nothced for clearing either the 3800 SC throttle, or the 3.4 DOHC intake's slight interference on the passenger side. Othere engines may have similar clearance issues. These two beams actually extend lower than the hinge mount on the fastback, towards the rear of the car. I'm pretty certain a stock 2.8 would clear the 84 decklid with no issues, but the center vent would be basically useless, as the engine would block the vast majority of it.
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Report this Post09-01-2015 06:02 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, and as mentioned before, would allow rain direct on the front half of the engine. Someone modified the 84 decklid to help shelter the engine from water and debris. Maybe CowsPatoot?

I did notice that the passenger side beam on the notchback was shallower in the area where the SC pulley would be located on a swap.
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