In the upgrades buy the first performance upgrade. Then go back to the stock equipment (don’t install the stock upgrade) and then hit the RIGHT TRIGGER then the A button soon after you hit the RT. This will make you go to the last or most advanced upgrade.
I don’t know what happens but the game will ask you if you want to install the stock parts but in the background you can see that you are on the highest performance part. Hit A to install and you will see that you have the hi-pro upgrade for the price of a level 1 performance part. Now sell your first upgrade that you bought.
You can upgrade a car really cheap. I found this out when I was buying tires. I changed the P.I. of my McLaren for a Spec race. I was selecting a tire compound and I hit the LEFT TRIGGER and it was going to the left and I hit the A button before it got to the stock parts and it went to the screen were you can select a tire company ON THE STOCK parts option. I was like WTF. You cant select tire companies on stock tires. Well now you can. I discovered that the P.I. changed on a ‘all stock car‘. Not by much thought. So you can get an edge on Spec races.
If anyone eles finds something by using those LEFT and RIGHT TRIGGERS PM me.
You cant sell the part. If you try it will ask if you want to sell it for 0 cr. AND if you install another part for that item the wrench will disappear and you will have to do it all over.
Let me know if this work for you guys. I have one of the first 360 that came out and I had to send it in twice to be replace so I am on my 3rd xbox. So I might have something wrong with my system or maybe not.
The thread was locked and edited because we reported this to the developers after we tested your error and were able to duplicate it. We appreciate the fact that you reported it, however rather than telling everyone about the bugs the more appropriate way to report it would be via email to forzafb@microsoft.com
You were banned because the moderators already told you to stop posting this bug on our forums in order to stop the spread of folks exploiting this bug. Even if we were going to fix it with a patch in the future, it would be nice to keep this info low key as to not ruin the experience for others.
Forza 2 Cheap performance upgrades!! 
Linear Mode
