Deadeye

I am looking at improving down force at the rear of my 911. I currently have an air dam that closes off the front fairly well, but only have a duck in the rear. Should I add a wing to the duck, or find a turbo whale tail?

winders

Ducktail < whale tail < RSR 3.8 tail

Are there rules to be concerned with here?

Deadeye

No rule book to comply with (at least for now) just looking for a little more down force on the rear end.

winders

Most of the Spec 911 guys out here in Northern California are running the RSR 3.8 tail.

Scott

MUSSBERGER

It does give you adjustability which the others don't.

stownsen914

When you say "better for aero" do you mean making the car "slippery" and aerodynamically efficient or getting more downforce? The 3.8 wing will certainly give the best downforce. The ducktail will give a bunch less downforce, but is good for aero efficiency on the back of a 911 due to the car's sloped off rear, which induces a good bit of aero drag and lift without some kind of wing/tail.

There was an aero comparison done many years ago (maybe by Porsche?) showing the aero efficiency/drag and downforce values for an early 911 with no aero, with a duck, and maybe with a whaletail too. I think with nothing the 911 had a couple hundred lbs of lift at 140 mph (or whatever the test comparison speed was), and the duck made that mostly go away. So in essence provided a couple hundred lbs of downforce AND made the aero Cd go down.

You'd get more downforce than that with a whaletail, and probably more again with a 3.8 tail. Not sure about the aero efficiency/Cd comparison between those two.

Scott