Mustang Forced Induction Install - Feeling the Pressure

Hacking the System

Today's hot-rod world cannot exist without computer-tuning capabilities in large part due to the emissions controls and sensors in the OBD-II style computers. Thankfully, there are several companies on the market today which offer products that allow tuners to hack the factory processor and reflash it with a modified tune-up.

The Paxton blower kit came with a DiabloSport Predator that has a blower-friendly tune-up already installed, but we chose to go with a custom tune, and Job Spetter Jr. of Turbo People was tapped for this task. We had changed the fuel injectors, and that made the Paxton-supplied tune obsolete. Spetter also massaged the Saleen's computer system, so the car drives properly with the turbo system installed and makes copious amounts of power.

"It is imperative to tune the computer in these cars when adding something like a blower or turbo, otherwise the engine will blow up," Spetter says. The old days of just jacking the fuel pressure and running an FMU on the 5-liter engines are gone. "The computer in the new cars is more complex than the previous generation EEC, and although there are more parameters to tune, once you get a handle on it, the final product is much better to drive and perform," says Spetter about the S197 computer system.

He told us what he adjusted to get these cars to run properly, "I worked on getting the MAF transfer function calibrated to the desired air/fuel ratio. What that means is, you tell the computer that when it sees X amount of air in the MAF sensor, then supply X amount of fuel. The most important part is getting the mass airflow correct. [Hellion and Paxton] did a great job with routing the bypassed air back into the system when you come off throttle. The recirculated air doesn't disrupt the MAF sensor reading." The bypass valve prevents air from backing up into the blower or turbo once the throttle blade is slammed shut. Since the air has been metered, it cannot be vented to the atmosphere and has to be reintroduced to the intake tract.

We probed Spetter for the differences in tuning the blower and turbo cars, and he responded, "Sorby's car was more involved because he had a DiabloSport MAFia added on. The MAFia changes the signal from the MAF sensor. The load tables are also different with the turbo because of the aggressive torque curve-it is similar to a twin-screw or Roots-style blown car."