On the dyno, the Si is an impressive performer, as it produced more boost from 3,000 all the way to 6,500 rpm using the same 3.00 blower pulley. Our '96 Cobra test subject produced baseline numbers of 587 rwhp and 497 lb-ft of rear-wheel torque at an average boost level of 16 psi. With the Si-trim head unit pressurizing the top side of the engine, power production rose to 615 rwhp and 550 lb-ft of torque at the wheels with an average of 19 psi of boost.
"Vortech did an excellent job because it improved power all the way through the powerband. It's easy to make improvements at the top end," says Anderson Ford Motorsports' Rick Anderson. "The way it picks up at the low-end-a street guy is going to feel that big time. It's really neat that they went back to a non-current blower and made it better." We agree with Anderson.
For a model update, the Si is super impressive, and the improved performance should keep your Mustang ahead of the competition.
The Business of Boost
Rick Anderson took the liberty of recording the boost level on each run before and after the Si swap. You can easily see that the Si is making more boost earlier, and continues leading all the way to redline.