I read something about using a stock 1982-92 Firebird rear wing as a rear under-bumber diffuser but I can't find any picture of this installation.

Somebody have one?

This is this spoiler I am talking about.

Under bumper diffuser? The '86 Firebird that I had years ago had the same spoiler/wing. The lower surface of the wing had a slight camber and (at very high speeds) would (in theory) generate a download... provided the airflow over the roof and rear glass was relatively clean. The wing was for looks. Most of us don't travel at speeds where any significant aero forces are likely (especially here in the DC area
If you're concerned about drag issues under the car, the turbulence generated by the cradle and trunk well will override any benefit from a diffuser. For the Fiero, the nearly vertical rear window will create a flow separation point which will tumble the air long before it gets behind the bumper. My advice would be to spend the money on upgrades that will actually help performance or appearance.

Just advice from an old man. Jimmy
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1987 coupe; Blue; 2.5L; 5-spd
1987 Firebird Formula; Blue; 5L; 5-spd

[This message has been edited by Macarchie (edited 10-07-2013).]

I've seen a couple. One with it just mounted down there and this one with it mounted and molded in.



Neither of them are mine though.

That picture brings back memories - I had a Firebird that looked near exactly like that in high school. Was one of the first cars I bought.

quote Originally posted by Macarchie: If you're concerned about drag issues under the car, the turbulence generated by the cradle and trunk well will override any benefit from a diffuser. For the Fiero, the nearly vertical rear window will create a flow separation point which will tumble the air long before it gets behind the bumper. My advice would be to spend the money on upgrades that will actually help performance or appearance.

Yeah I have to agree with this.

The Fiero's rear trunk was designed to accommodate placing one of the normal size wheel and tire into it in case of a flat in case of emergency, since you cannot place the normal size wheel and tire in the spare's location. The trunk had to be designed to be rather large. Because of it's large size, any air going to the trunk would be blocked or forced to the sides of the car. However, not that much air gets back there anyway. It's primarily due to the car's design. Air traveling under the car doesn't work like a normal uni-body vehicle. When air traveling underneath the Fiero's space frame meets the opening where the drivetrain is, the air gets forced upwards and through the vents of the decklid. This air going through the decklid eventually meets the air coming over the car. There's a bit of a neutral pocket around the window area, but there is a meeting point between the air going over the car and the air coming from under it.

If you have looked at other similar mid-ship vehicles that are well established, like the MR2 and Lotus cars, you'll notice that rear aero is not focused on much. It's probably because these vehicles experience similar phenomena as the Fiero does. Some thought could have been placed into more intricate rear aero for air flow, such as is on many mid-ship exotic cars, but if that would have been the case there would have potentially been little to no room for a rear trunk, thus destroying most all the Fiero's cargo capacity.

That rear diffuser looks nice, but I doubt it will do what you want it to.

The air that flows past the cradle instead of up the firewall, is drawn upward behind the car into the vacuum created by the speed.

That air then flows forward under the wing along the top of the deck toward the window where it joins the air spilling off the roof
and tumbles creating turbulencr behind the window.

The diffuser would enhance the vacuum and cause the air to tumble behind the car instead of travelling up the bumper like stock does

But, at street speeds, this is not a big deal IMHO and the trade off for the looks might be a nicer improvement to modernize the look

Arn

I thought real diffusers were supposed to have vertical bumps or fins.