Dale Amy
September 1, 2003

Horse Sense:
Production cam specs vary between PI and non-PI applications. PI intake lift increased from 12 mm to 13 mm, while exhaust lift grew from 12 mm to 13.75 mm. Interestingly, PI cams have 4 degrees less intake duration than their non-PI counterparts (252 versus 256) but are unchanged in exhaust duration.

To date, cam offerings for modular Mustangs have been relatively few and far between- perhaps not without good reason, since a cammer cam swap will take a sizable bite out of the old savings account. It therefore had better offer a healthy power-dividend return on that investment. Quite honestly, the factory engineers seem to have developed a good all-round cam package for the late-model GT, much as they did with the 5.0's H.O. cam.

Sure, the SOHC runs out of breath a little early, but, in compensation, it churns out decent torque down low, delivering outstanding economy in the process. For street purposes, on an otherwise-stock 4.6 Two-Valve, our guess is there's likely not a whole lot to be gained from a cam swap. But with the number of mod cars now flocking to the dragstrip, and particularly with the popularity of forced induction on both SOHC and DOHC Mustangs, we predict a growing niche for cammer camshafts.

In the past couple years, Dan Millen and his cohorts at Livernois Motor-sports have been aggressively pursuing modular performance and have recently introduced their Stage 1 SOHC cam-shafts. These camshafts are said to work with any '96-and-up Two-Valve, but they are optimized for use with Liver-nois' ported PI heads. In com-parison to the stockers, the Stage 1 grind has both more lift and duration in an effort to raise the power peak from 5,500 to about 6,500 rpm, but it retains the stock lobe separation to maintain low-rev torque.

In the midst of the winter racing off-season, Livernois installed a set of these new bumpsticks-bracketed by before-and-after chassis-dyno testing-on Roxanne Shepard's Canary Yellow '99 GT racer, known to her fellow quarter-mile competitors simply as "Tweety." Our accompanying photos show that a modular cam change requires a lot more complicated surgery than would a pushrod. However, as you'll see, the results on Tweety were highly impressive to say the least.

But before you get carried away with unbridled euphoria, remember that Tweety's engine had additional modifications, including supercharging (see sidebar, Tweety on Steroids) that were clearly able to take advantage of the cams' revised valve programming. As with any cam swap, less modified engines would, in all likelihood, realize less dramatic gains.

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Tweety On Steroids
As have most race cars, Roxanne's GT has evolved over the seasons. When it rolled onto the Livernois Dynojet for our baseline testing last winter, Tweety already had the fol-lowing modifications/enhancements:

  • Livernois Race Engines-built 4.6 Two-Valve 0.020 over-bore (285 cid) with JE Pistons, Cobra crank, and Eagle H-Beam rods
  • Vortech SQ Supercharger with Aftercooler
  • Anderson Ford Motorsport Power Pipe
  • K&N air filter
  • Ford Racing Performance Parts Bullitt intake
  • Accufab throttle body
  • FAST Electronics fuel-injection system
  • Weldon 2025 fuel pump
  • Creative Performance Racing 72-Ib/hr fuel injectors and fuel rails
  • MSD coil-on-plug ignition system
  • Anthony Jones Engineering K-member
  • ARB/Reider Racing air locker differential
  • Precision Gear 4.10:1 ring-and-pinion
  • Precision Industries 10-inch converter,- 4,000 stall
  • Performance Automatic C4 transmis-sion with transbrake
  • MAC long-tube headers
  • Dr. Gas X-pipe
  • DynoMax mufflers
  • Royal Purple 5W30 motor oil, Max ATF transmission fluid, Max-Gear oil, Purple Ice
  • Tires and wheels by Harlow Racing Tires & Wheels

Bumping Up The Power
Stock CamsLivernois Stage I CamsGain

Well, you can see that the Livernois Stage 1 cams not only raise the rpm envelope, with eye-opening gains of 85.7 hp and 68.9 lb-ft at 6,500 rpm, but they also did well right across the board. In baseline form, power began to fall off above 5,100 rpm, while the Stage 1 cams bumped the power peak to 6,200. Though it doesn't show on our chart, the torque peak of 456.6 lb-ft occurred at 4,400 rpm.

We spoke with Roxanne Shepard after Tweety's first '03 race outing in Florida, who said the power increase "feels huge" on the track, and thought she might need to revise ring-and-pinion gearing to take best advantage. Tweety went 11.08 at 123 mph at Bradenton. Roxanne says last year's times in similar air conditions were typically in the 11.40 range.

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