Factory rear spoilers - Mid/Late 70's GM - do they work?

[wheels777]

My son and I are working on a new project.  Very cool to hang out with my teenage son and a buddy from high school.  We have some very good kids who will be coming behind us and keep the racing sport alive.  The boys have some ideas on an engine that we are going to try and (while money is very tight) I don't mind spending a little money on something that may or may not work, knowing that we spent some good quality time together.  It so cool that my teenage boys still want to hang out with Pop and there friends do too.  ANywho, I /we have some questions.

We were discussing the merits of the mid/late 70's rear spoiler (Camaro, Monza, Firebird, etc.).   
Looks like they would reduce rear lift and increase drag.  Is this correct?
How much Cd points do they add?
Is there a speed below where they are not worth adding?
Is there a speed above which they are worth adding?

[RichFox]

I can only comment on the factory optional read spoiler and front air dam for a '77 Vega. On my cat I had to increase the rating of the rear springs because of the spoiler pushing the car down enough in the rear to cause tire scrape. I had about 2 inches when standing still. So it seemed to be working to me.

[Leadfoot]

I think GM did some testing on the 1969 Camaro , try goggleing Camaro aerodynamics I remember seeing it somewhere. Thanks

[Stan Back]

Steve Batchelor ran 250s with a factory spoiler on a stock wheelbase Monza without problems to about 10 BV and El Mirage records.  How fast are you planning to go?

[wheels777]

Nyshe.

I have heard/read that these cars typically have rear lift without the spoiler and a small amount of down force with the spoiler.  I don't plan to run that fast (250), but would like to be stable and safe at over 200.  Any help is appreciated.

[Stan Back]

Steve Batchelor set tons of records and ran into the 250s with a stock spoiler on his Monza.

(An answer at last!)

Stan