The story was short on the 1999 Black 5.4 GT Mustang. I ended up selling it. I wanted the cash to pay for something else so someone made a offer on it and I let it go. The guy brought it back to me a few times to get change the tune. I got my quarterhorse back out of it and gave him a F3 chip as part of the deal. He actually put a supercharger on it, a Saleen M90 4.6L supercharger kit that he got for a good price. I was rather unimpressed. That supercharger was too small for a 5.4L. It gave it some great mid-range power, but it drops off fast after about 4500 rpm. I believe the supercharger is becoming a restriction at that speed, as it can't feed the beast enough air.
He actually paid a professional shop to tune it before he brought it to me. It was in bad shape when it arrived. Only dyno'd 280hp to the wheels. Turns out they had vacuum leaks everywhere on the used kit, the belt routed wrong, and the bypass valve was broken in the open position, the intercooler was bad. Lots of little things. Then this supercharger was put on top of a 11 to 1 compression 5.4L running on premium - I had to pull 10 degrees of timing or more across the board to stop the spark knock. Poor car. I think his next adventure is converting the car to run on E85. He'll need to get bigger injectors, but the extra fuel and octane will allow me to put more timing in and keep cylinder temperatures down a bit.
As far as me, I purchased a new Mustang. Well, new to me. A guy brought by one to the shop and needed engine work, decided to sell it. That car got a Saleen supercharger put on, which was underwhelming. Eventually I put together a low-budget 4.6L 4 Valve DOHC engine similar to the Cobra models with the use of 2001 Cobra Heads, 97 Mark VIII block, and 2004 Mach 1 intake. If you liked this post, you should come over and read about the $300 Mustang Project.