How much should I retard my TIMING?

Actually I was talking to Don and he was telling me that they were going to have a Dyno day soon.. Well he was trying to set that up, so i will go then.. Don is doing my chip now so I will retard the timing a little to prevent detenation..
 
JD's is expensive, he quoted my friend 14,000 for a turbo install on a 2000 GT. With a kit costing about 5000 I'm still looking for $9000 in tuning and labor..
Here's the pinch. He told my buddy, that he wanted to dyno the car before and after to show him the diff in HP. He wanted to charge my buddy for the first run. If you want to show me the diff on my car and I didn't ask for you eat that cost, all i want is results and a good tune..