We have the 3.90 gears in one car and the stock 3.3 in the other, both cars are otherwise identical, Whipples, exhaust, brakes, short shifter…
The stock geared car is as most everyone knows is long legged; getting 0-60 without a shift will do that. The torque the GT has masks this as to not be a real issue and as we know most people are very happy with the car as is. The 3.90’s surely aren’t for everyone but once you drive one it’s obvious why they have their place. On the road it seems to always be in the heart of the torque curve, a very responsive car in any gear at any speed. Sure my fuel economy took a small hit but my right foot does more damage! How many drive a GT like a prius? On the track it is fantastic, everything it does for the streetcar is exponentially better there, I really can’t overstate how much I enjoy it. Running the mile does require a shift into 6th 400’ from the finish, so not so good but that’s a rare occurrence and it did get me over 210. The stock geared car is still pulling 5th and is the winner there.
As for the cost Kendell is in the same ballpark as the originals. This isn’t ordering a ring and pinion off the shelf, per unit cost, as before, is going to be up there, frankly building only 20 sets I would think most vendors would consider a waste of time so its going to cost you.
The gear change is one of, if not the best mods made to the car, it isn’t seen or heard but it’s felt and it makes me smile.