I doubt that a diffuser would be effective. Between the relatively high ride height and lack of an underbody tray, the airflow would be very turbulent and not very effective at creating downforce.
The Ferrari F360 generates about 200 pounds of downforce on the rear wheels, but remember that it has a completely enclosed undertray to smooth the airflow. It was also designed with a diffuser and needed over 5000 hours of wind tunnel testing.
Unless you routinely pull 1 G at triple digit speeds, I think any diffuser would be cosmetic anyway. IMHO, if it doesn't work, don't rice out the car by adding useless aero tweaks.
Roger that. I prolly won't be getting ovef to Nurburgrin, or Spa any time soon. However comma I am routinely doing 140+ thru T-1 at Seattle, where it is an up and over and down to the right kink, that might gain me som needed stability. And if I can get over the 65-75 in T-2 at Seattle, and 77-82 thru T-1-2b at PDX, the highest speed turns after T-1, then it might be worthwhile. There's a guy on Wheel2Wheel who has some design info. You just have to span the distance from the belly pan to the back of the crossmember to diminish turbulence, then kick it up at 7Deg. and you might get soem downforce. Any brainiacs on this list who can figure it out for the Z with 1.5 inch lower ride height?