From how much power do you talk?In a drag race, at a HP level that we're likely to see, downforce is not needed, and drag is to be minimized. A clean trunklid is faster than an adorned trunklid in a straight line, up to a certain point (which is far greater than the power any of us is likely to put down).
JR
Like, double that, or more. Top Fuel dragsters have massive wings to provide aero grip to their massive tires and direct airflow to keep the car inline, because they're making upwards of 10,000 horsepower and traveling at 300+ MPH. Any street-capable Mustang is not going to hit those crazy speeds in the quarter mile, and probably won't even hit half of that, so really, anything on the back of your car that isn't like the one in the link below is just adding drag and slowing the car down. Now, if you're doing standing mile competitions, that's a little bit of a different story, but even so, you're probably not topping 180 MPH in a standing mile unless you're making over 1,000 HP and severely minimizing drag. Hennessy hit 200+ in a 2015 with a massive supercharger, and taped over every external gap and potential source of drag.From how much power do you talk?
My car has at the moment 740 HP and 634 lb torque.