when do you "need" one? or what times/ speed should you run one. how much et does this help?

 

I believe its all about the speed rather than the times. 170 and higher i would say its a stability aid to help the air move past the rear.

 

thanks i figured around 140+ ill stick to my cf spoiler then its at least longer then stock lol

 

It's to help with rear end traction at higher speeds, aka stability as SPOOLINmatt said above.
The curves of a car create downforce on the front and lift on the rear. the faster you go, the stronger the forces. 150+ I believe is where it really starts to become noticeable, and 170+ it becomes borderline dangerous.

A rear spoiler is meant to create downforce at lower speeds (below 150), hence the actual angle to it, but it also creates some drag. at 150+ a spoiler hits it's stall point and causes more harm them good, creating less downforce, and stupid high amounts of drag. Twisted spoilers create almost as much downforce as a standard spoiler, but with much less drag, as it's twisted to work appropriately with the different airflow angles around and over the car.

A drag spoiler is flat[ish] because it is meant to create as little drag as possible, and not create a lot downforce, but just enough downforce to negate the lift created by the curve of the car, plus a hair more depending on adjustment.

they also help with proper chute deployment. incorrect airflow behind the car can cause catastrophic chute failure.

 

We run a Round2Motorsports drag wing on my DC chassis and it helped stabalize the car pretty well on the big end. were regularly seeing 150+mph

 

ya im not to those speeds yet thanks for everyones input.

 

So for all motor cars going <150mph it doesn't matter as much? We run the Spoon Sports CF wing going 144, the FCS piece looks nice, just not on a 92-95 hatch!

 

It helps regardless IMO. More stability is always better plus it helps aid in getting the turbulent air away from the rear of the car which creates drag on the car