Here is the reply to your question from the FFR Forum
posted June 20, 2007 07:56 AM
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I posted a link to an Excel spread sheet calculator that I wrote in another thread.
Here is the link again
http://putstuff.putfile.com/84101/4299774
enter your data in the yellow fields. The transmission ratio's that are already there are for the TKO.
Look at the graph that shows torque at the rear wheels you want to shift when the torque is higher in the next gear than the gear you are in.
The graph gives you speed in mph then look at the speed in gears graph to get rpm.
You can stretch any graph to make it easier to read.
You will need to do your own test to see how much rear wheel torque your car can put down through the tires to the pavement by flooring it at different rpms.
steve