Coupe/Formula Front End Aero

[Series8217]

I'm doing a track weekend at Willow Springs on May 4-5. This is a pretty quick road course (it's called "the fastest road in the West"), so I will likely be seeing speeds of over 120 mph.

My current '88 Fiero has the coupe nose. Aero is all stock besides not having the spare tire tray installed. No wing. With my old '88, I vented the hood which did a lot to reduce front end lift, and it felt stable above 120 mph. Without the hood vent the front got pretty light.

I'd prefer to not cut a hole in the hood right now, so I'm looking for other aero options for the front such as air dams or front splitters.

For example, something like this: http://realfierotech.com/phpBB/viewtopi ... 60#p145232

However, I need to still have proper cooling. This isn't for drag racing, but 20 to 30 minute road course sessions in the desert. I can't block the radiator.

Ideas?

[CincinnatiFiero]

Could you pick up some spare headlight doors and cut some vents into those? Since the headlight doors blow open at high speed that high pressure area is also under the headlights, so Id thinking a vent there would also relieve some of that pressure.

[Shaun41178(2)]

Pretty good idea with the headlight doors. If racing during the daytime the light housings won't be necessary so removing them can save weight and you could put in different lids with holes fit in them.

Or you could go a more expensive route and do front coilovers and lower the car down for the race. A front air damn could also be installed. Just a couple ideas real quick

[The Dark Side of Will]

The Fiero aero problem stems from a large volume of air having to make a ~135 degree turn to come out of the radiator and then go under the car. This creates a high pressure area between the radiator and the spare tire well. The space in front of the radiator is reasonably well dammed and isolated from the space behind. The space behind communicates with the head light buckets, which is what causes the headlight doors to open at speed.

Venting the hood or headlight doors allows this high pressure air to escape without creating front end lift.
I have two problems with hood vents:
1) They vent hot radiator air right to the air conditioning intake at the base of the windshield.
2) They attract attention.

A quick/dirty track day solution might be to remove the headlight doors for the day.

I've been thinking of mods that would effectively duct the post-radiator volume to vents high on the fenders, similar to the "Z3 style" vents that ricers put on Civics.
The potential drawback I see to this is that it may elevate engine intake temps... I have my Bluetooth OBDII interface now, so I can datalog IAT and see if it goes up relative to ambient when I do this mod.

Step 1: I'd start by cutting a 3 or 4" hole behind each headlight motor in the steel bulkhead that separates the post-radiator volume from the spare tire well. Right in the middle of the 4 bolt mounting pattern for the motor assembly would be a good location.

Step 2: I would then build a vertical partition that would go from the steel wheel house at the bottom to the underside of the hood at the top, and from the bulkhead at front to the firewall at the rear. The partition would divide and mostly seal the volume outboard of it from the rest of the spare tire compartment. Doing this on the right side of the car would require relocating or removing the windshield washer reservoir.

Step 3: I plan to cut a 3 or 4" (or the largest I can fit) hole from the volume I just created out to the volume between the plastic fender and the steel body. This hole would be straight outboard, right in front of the firewall, just below the upper frame rail. It would be right underneath a fender vent in the "Z3 position".

Step 4: Install a tastefully subdued vent, like the Z34 Lumina hood vents into the fender at this location.

[ericjon262]

here's an old school solution, take the weather stripping off spare tire compartment and cowl. re-install after the race and you're good.

[fieroguru]

On my 88 coupe I drilled a couple of 3" holes in the side of the head light buckets to vent the air inside the fender area, then drilled three 3" holes in the wheel well liner... it helped, but my headlights are still popping up. I think this method would work better with the headlights removed so they are not impeding flow to the holes. I might try adding another 3" hole down by the front and a 2" one between the wiring pass through hole and the top 3" hole (just have to stay low enough to clear the frame rail).

[ericjon262]

doesn't someone make little cables that hold the doors down?

[The Dark Side of Will]

That doesn't solve the aero problem... it just holds the headlight doors down.

It probably makes front end lift WORSE, actually.

[ericjon262]

That doesn't solve the aero problem... it just holds the headlight doors down.

It probably makes front end lift WORSE, actually.

true.

[Series8217]

I will be getting some Alumalite (aluminum sheets sandwiching a plastic honeycomb, used for outdoor signs) next week to build a splitter with. I still need to find a good material to shape the air dam with. Some flexible plastic would be nice, but I would need a way to secure it to the splitter or front fascia.

here's an old school solution, take the weather stripping off spare tire compartment and cowl. re-install after the race and you're good.

Interesting idea. It would totally kill my AC even worse than venting the hood, but it might let some air out.

I've been thinking of mods that would effectively duct the post-radiator volume to vents high on the fenders, similar to the "Z3 style" vents that ricers put on Civics.

I may try this if I can find some fenders at the junkyard this weekend, and if I have time.

Could you pick up some spare headlight doors and cut some vents into those? Since the headlight doors blow open at high speed that high pressure area is also under the headlights, so Id thinking a vent there would also relieve some of that pressure.

Good idea. I could even just remove the headlight doors.

[ericjon262]

see, that's the beauty of removing the weatherstripping though, it's so easily reversible, you don't DD at speed great enough to matter do you? remove it for track days, reinstall before leaving the track.

[Series8217]

see, that's the beauty of removing the weatherstripping though, it's so easily reversible, you don't DD at speed great enough to matter do you? remove it for track days, reinstall before leaving the track.

Well, AC is kinda nice at the track when its over 100*F outside.

[ericjon262]

see, that's the beauty of removing the weatherstripping though, it's so easily reversible, you don't DD at speed great enough to matter do you? remove it for track days, reinstall before leaving the track.

Well, AC is kinda nice at the track when its over 100*F outside.

I keep forgetting that you road race/autox/drive more than just straight lines...

[AkursedX]

Out of curiousity, has anyone actually verified that venting the hood in a Fiero 'kills' the A/C? I understand in theory that it would be sending hot air over the collector, but I do not have a wind-tunnel or real-life experience that indicates that the A/C would not be sufficient. Also, with a vented hood, air is moving more efficiently through both the rad and the condenser so that *should* help with the efficiency of the A/C system.

I did some searching through the .nl and couldn't find any tests that verify claims either way. I have been at over 130mph stock and then with my front decklid unlatched. The front decklid would rise 3-4" at high speeds due to the massive amount of air that runs through. The popped decklid resulted in much greater stability at those speeds. The extra stability that is gained at high speeds would trump any loss of A/C effectivness any day of the week IMO.


As for air-dams for the newer coupe nose, I haven't seen much of anything for them. The old bumper pad noses had a manufacturer for a lower air-damn. I think the company was called Pegasus Engineering. The easiest/cheapest thing I could see being done is riveting up a piece of flat plastic to the black lower part of the nose effectively making that airdam lower.

[The Dark Side of Will]

Out of curiousity, has anyone actually verified that venting the hood in a Fiero 'kills' the A/C? I understand in theory that it would be sending hot air over the collector, but I do not have a wind-tunnel or real-life experience that indicates that the A/C would not be sufficient. Also, with a vented hood, air is moving more efficiently through both the rad and the condenser so that *should* help with the efficiency of the A/C system.

I thought that Steven had found that the hood vent made his A/C much less effective.

The cabin air inlet is right at the base of the windshield. I don't see why hot air from the radiator would NOT go there. Starting with air that's that much hotter is not going to help the system efficiency any, even if there's better circulation through the condenser.

Edit: "Effectivness" meaning discharge temp, not efficiency.

[AkursedX]

I thought that Steven had found that the hood vent made his A/C much less effective.

The cabin air inlet is right at the base of the windshield. I don't see why hot air from the radiator would NOT go there. Starting with air that's that much hotter is not going to help the system efficiency any, even if there's better circulation through the condenser.

Edit: "Effectivness" meaning discharge temp, not efficiency.

I found THIS as the only topic where something was mentioned.

Turning the dial to cold works when there is cold air to suck in. With a hood vent you suck air which is like 30 degrees over ambient. It sucks. Especially in the summer. I know because I had a hood vent on my silver car and no AC.

Apparently Steven's silver car had no A/C. Although he obviously felt the warmer air come through. How much difference would the A/C make? I don't know. But, I have not found any information on the topic at all on the topic. I checked for topics with NSX's, Porsche's and MR2's and I couldn't find anything in regards to diminshed A/C. I did find THIS that had a computer model indicating the advantages of venting the hood of a 911 (Being Air-cooled, it only speaks to the potential aero advantage).

[Series8217]

That's a good point. My silver car didn't have AC so all I directly felt the HVAC inlet temp difference. With the Fiero having so much excess AC system capacity it may still work fine, although obviously it would be less efficient. I have an R134a variable displacement compressor from a mid-90's Z34.

[Series8217]

I did some searching through the .nl and couldn't find any tests that verify claims either way. I have been at over 130mph stock and then with my front decklid unlatched. The front decklid would rise 3-4" at high speeds due to the massive amount of air that runs through. The popped decklid resulted in much greater stability at those speeds. The extra stability that is gained at high speeds would trump any loss of A/C effectivness any day of the week IMO.

I like this idea because it's stupid simple to implement safely and is completely reversible. I would just have to have some sort of cable to prevent the hood from flying forward / open in the event of a spin. It could limit the decklid to an inch or two of opening.

[ericjon262]

how about a set of hood pins adjusted way up?

[Series8217]

Sure, but that's not reversible.