Dale Amy
December 1, 2002

Horse Sense:
Boost must be accompanied by timing retard since it raises both cylinder pressure and temperature, the prime causes of detonation.

When we left off, our '95 GT ragtop had just been given the gift of boost in the form of Paxton's potent Novi 2000 centrifugal supercharger ("Winds of Change," Mar. '02, p. 71). Through our J&P-ported Edelbrock Performer heads and intake and MAC long-tubes, the out-of-the-box Novi huffed and puffed its way to more than 435 rwhp at a mere 5,700 rpm-the point at which we had no choice but to get out of it. Trouble was, during dyno testing, we quickly found and exceeded the limits of our convertible's fuel and spark systems. We had no means of boost retard onboard and, under double-digit boost, our ACCEL 40-lb/hr injectors were able to dispense fuel faster than the Novi kit's 255-lph in-tank fuel pump could supply it. And, in a final fit of unpreparedness, we had no chip. Just another day in the life of a magazine project, but all things considered, it's a wonder the small-block survived the dyno session intact.

Though we were able drive it on the street, fear for the health of our stock hypereutectic pistons limited us to part throttle and about 4,000 rpm, because introducing 10 psi of boost into cylinders starving for fuel under a factory timing curve would be a recipe for certain meltdown. On the bright side, driven in this pansy, balloon-foot fashion, the GT had no really bad manners other than a determined proclivity for stalling at hot idle and a tiny bit of light throttle surge. But good manners are of little comfort when you really just want to hammer the thing. After an intervening six months of winter storage, it was finally time to address our support systems' shortcomings, so that-hopefully-the only items at risk under full throttle would be the rear tires, the factory clutch, and our drivers' licenses, not necessarily in that order.

For our '95 5.0, we are using MSD's combination of 6-BTM (Boost Timing Module) capacitive-discharge ignition box (PN 6462), Blaster TFI coil (PN 8227), and TFI coil harness (PN 8874). The 6-BTM's timing control knob allows dialing-in between 0 and 3 degrees of timing retard for every pound of boost the unit detects. Through experimentation, Lidio Iacobelli ended up pulling about 1.3 degrees per pound, for a total retard of around 13 degrees at our Novi's observed max of 10 psi.

We could have gone overboard with some sort of aftermarket EFI and a whole new stern-to-bow fuel system, but unlike most of this magazine's other projects, this one is strictly a street vehicle and is therefore unlikely to gain much more power, so we decided to take a minimalist approach. We polled the supercharger-savvy crew at Lidio Iacobelli's Alternative Auto, who suggested all we really needed was MSD's well-known 6-BTM boost-retard ignition box, one of Vortech's equally ubiquitous T-Rex inline supplementary fuel pumps, and one of Lidio's blower-friendly electronic tune-ups. Lidio favors Mike Wesley's Autologic chips and tuning software, and since we'd had little prior experience with the Autologic system, we were anxious to try it firsthand. Judging by our results, we think it was a good choice.

Check out the accompanying photos for a look at the hardware installation, and our tuning sidebar for the story on Lidio's approach to a powerful, but safe, forced-induction tune-up. We now have a Viper killer with all the manners of a stock GT.

Electrons In Order
In the past decade, Alternative Auto has installed tons of blowers on both pushrod and modular Mustangs, so when it comes to knowing what it takes to tune for boost, Lidio Iacobelli is a good man to talk to. Lidio is of the street-tuning philosophy, meaning he plugs an air/fuel ratio analyzer and a laptop into the car he's tuning and drives it around extensively, under cold, hot, idle, part-throttle, and full-throttle conditions, instead of using full-throttle pulls on a chassis dyno or just generalized guesswork. For the A/F analyzer, he temporarily plumbs a pricey, wide-band oxygen sensor into the subject vehicle's exhaust.