I have a 1970 Mustang that I installed 620# front coil springs, Koni shocks, and did the Shelby drop. My question is if I need a negative wedge kit as well. What will the kit do for me if performance improvements would be seen? Thanks.
no you do not need the negative wedge kit. that allows you to drop the upper arm pivot another 1/2-3/4", and does improve handling, but at the expense of adding alot of stress the the upper arm right behind the balljoint where the arm was not designed to take that added stress.
Shelby saw fit to do this mod on the early cars, but I'm not real sure as to how it carries over in the later models. From what I've read, its not AS necessary on the later models, as Ford had corrected some of the geometry problems in the later cars, BUT, from what I've read, it will still help the later cars to a certain degree.
Wait for more input and possibly do some outside research. Rbohm may be right regarding the thickness of the shock towers being a concern on your model. However, 65 and 66 Mustangs weren't designed with this mod in mind and the success of the mod is well known at this point and is also prevalent. Regardless, it shouldn't be a major ordeal to add additional plating/bracing at the upper control arm mount, IMHO, at the same time you relocate your upper control arms.
As you know, the wedge kit is designed to correct the ball joint angle to reduce wear and prevent binding when lowering the arm. However, the 1" Shelby drop shouldn't cause binding (except maybe at full suspension extension). So, you shouldn't need the negative wedge. If you had lowered the upper arm more than 1" then you would have needed the wedge to prevent the binding. The wedge kit (as offered by Pro-motorsports) allows you to lower the upper arm further, which improves the geometry for better handling.
No one needs a wedge kit with a 1" drop. In my opinion a street car doesn't need more than the 1" drop. The money can be spent on other things that will bring more to the cars performance.
With a 1" drop, the upper arm will hit the bump stop before the ball joint binds, no matter what kind of spring you have.
Sorry, rereading this thread made me realize that I wasn't commenting on the shelby drop but was commenting on the negative wedge system. It was late, and I think I had a few too many. These guys are on the money as to your need for a negative wedge setup.