Tom Wilson
January 1, 2003

Horse Sense:
While turbos muffle the exhaust, they make noise of their own. With whistling from the intake, whooshing from all the pipes, and a big ssssssh from the pop-off valve, this twin-turbo setup has a definite presence.

Chris Barnes was clearly thrilled about the power his 1,253hp twin-turbo small-block put out, yet in a bit of shock about it as well. After years of scrounging together parts, laying out acres of green cash, and jumping through the flaming hoop of technology several times, suddenly The Engine was a real and formidable entity. Chris now thoroughly understood he was going to have to strap it to his back and step on the loud pedal. Hmmm.

That, and how in the world did all this come about?

Well, it transpired in the usual way, through a bit of craziness and a lot of hard work. Because you are reading this magazine, we don't have to explain the crazy part. The hard work, well, that's as simple as putting a working man's fun budget into the "Speed costs money-how fast do you want to go?" formula and making the necessary calculations for "really fast."

When Chris bought his Cartech Twin Outlaw turbo kit, it included 131/44-inch primary headers collecting into four-bolt TO-4 flanges and wastegate mounting assemblies. After the turbos, the so-called "down pipes" are 3-inch units, flaring to 311/42 inches right before the muffler.

A mining-equipment manufacturer's representative, Chris figured he'd do something a bit out there this time around with his clean, blue '89 Mustang LX. A Powerdyne had already been through the engine compartment, followed by a ProCharger. Why not install a twin-turbo setup and have a go at Wild Street? Well, if you live in Phoenix, Arizona, we can think of a couple thousand miles of reasons why, but what the heck, John Urist goes almost that far for Outlaw.

Not having a huge budget, Chris carefully shopped for good used parts, ending up with a second-hand but unused Cartech twin-turbo kit and all the parts for the basic engine. All told, Chris believes he has $12,000-$13,000 in the engine, which is real money, but in dollar-to-horsepower terms is actually quite reasonable. Scratch-built, dedicated race engines in this league can run twice that amount.

The "good-used" approach on a turbo engine is not so bad, because dedicated turbo engines are not exotic, just built from really strong parts. An A4 block bored to 4.060 inches, a billet Scat crankshaft whittled in the good, old USA to a 3.250-inch stroke, forged Ultralite Oliver rods, and forged JE reverse-dome pistons provide the stout foundation with a turbo-friendly 8.0:1 com- pression ratio. Breathing is via 2.05x 1.600-inch stainless steel-valved Edelbrock Victor Jr. cylinder heads and intake manifold, all given the usual light porting by Duffee Motorsports in Phoenix, Arizona. Displacement is 336 inches.

ProCharger was the source for the rather heavy-duty-looking pop-off valves. One of these is mounted near each turbo to vent excess boost pressure. A screw adjuster allows fine-tuning of the boost-release pressure, while springs inside the unit give a coarser adjustment. As delivered, the springs would not allow less than 14 pounds of boost, for example. Later, Chris changed these to allow 12 pounds at the low end while still giving him well over 20 pounds of boost on top. During the dyno test, the system was adjusted to a hair under 18 pounds.

Naturally, Chris needed those items normally thought of as extras on naturally aspirated engines but required in a high-boost turbo powerplant. The block is O-ringed with stainless steel wire, soft copper SCE head gaskets are used (along with Total Seal piston rings), and the designed rev limit is a relatively low 7,200 rpm.

Camming is where you realize you aren't in Kansas anymore. Chris sent the specs off to Cam Motion, which in turn sent back a 0.684/0.686-inch lift, 242/236-degree at 0.050-inch-valve-lift mechanical roller. The big lobes raised Chris' eyebrow, for sure, but he was on an Africa-sized horsepower safari, after all. The remainder of the valvetrain is a mix of Crower solid-roller lifters, Comp Cams pushrods, and Pro Magnum 1.6 stud-type bolt-down rockers, buttressed by a Probe stud girdle.

Providing the boost and visual excitement is the Cartech Twin Outlaw turbo kit. The turbos are TO-4 60-1 hybrids from Arizona Turbo, and the air-to-air intercooler is a six-core unit also from Cartech, as are the headers and air tubing. Going into the dyno test, where we caught up to the project, Chris said he was hoping the wastegates were set to "around 20 pounds," and noted the system was incapable of providing less than 14 pounds of boost due to turbo sizing and spring pressures in the wastegates. Happily, it turned out the system provided a safe but respectable 17-plus pounds of boost on the Stuska water brake. All boost was funneled through a garden-variety 75mm BBK throttle body.