HELP!! I think there is a glitch in my game!!!

I recently bought 2 cars on Forza and decided I was going to personally tune them myself. I bought the Mclaren F1 and the Ferrari F50. Now I went to upgrade the McLaren and I will not allow me to install the twin turbo upgrade. It will put the turbos on the car if I use someone else’s tune, but I haven’t found a tune I liked, therefore I wanted to tune this car myself. Here is the kicker I am having the same issue with the F-50 and my buddy bought this car at the same time as myself and he was allowed to install the twin turbo upgrade in his car. Any thought on how I can resolve this issue? ANYTHING will help because there are my two favorite cars and I want to tune them up myself.

http://forums.forza.net/turn10_postsm47061_Centrifugal-Supercharger-not-installing.aspx#post_47061