The 2006 Pontiacs in the Park event at Virginia Motorsports Park (VMP) in Petersburg, Virginia, brought out some of the wildest Pontiacs ever seen. And one of those was Lee Schwilm's '70 Trans Am racecar (seen on page 3) featuring a 397-cubed Pontiac engine with Ram Air V heads, a Vortech supercharger, and custom fuel injection. Lee got the notion of boosting his Firebird's engine while at an event in Texas where he saw a supercharged 5.0L Mustang tearing up the racetrack. But he knew applying that technology to his Pontiac wouldn't be cheap or easy.
Power-adders like a turbocharger or supercharger use an exhaust- or belt-driven impeller to pressurize the induction system and mechanically increase the density of a fixed amount of air/fuel mixture within the combustion chamber. The result is a denser mixture that is more tightly compacted during the compression stroke. Upon ignition, the intensity and duration of combustion is greater, which applies more pressure on the piston face during the power stroke, greatly increasing torque output throughout the engine's operating range.
What many hobbyists don't realize is "boost" is directly related to the volume of air the turbocharger or supercharger displaces and the efficiency of an engine's induction system. In simpler terms, boost is the restriction caused by the power-adder trying to force more volume through the induction system than the cross-sectional area will allow. A high-flowing induction system can allow for a denser charge with a lesser boost reading. A poor-flowing induction system, however, can create a higher artificial boost reading without increasing output. So we cannot assume that greater amounts of boost will always translate into additional power.
Power-adders typically increase the amount of stress placed upon virtually every engine component, so when building a forced-induction race engine, each piece must be carefully chosen to ensure it's durable enough to withstand the additional boost pressure and torque. This oftentimes means exotic components not always found in typical naturally aspirated builds. And mistakenly overlooking one minor area can lead to failure that might ultimately cost an entire engine.
So what should you do when building a forced-induction race engine? If you're like Lee, you seek the advice of an experienced hobbyist with a long list of credentials, someone like Grosse Pointe, Michigan-resident Tom Vaught. Tom is a long-time supercharger engineer for Ford Motor Company. In some way, he has assisted myriad professional and hobbyist racers who've successfully campaigned supercharged engines over the years.
Lee took notice of Tom's expertise and asked him to apply it to his supercharged Pontiac build. Tom's experience throughout his years as a boost engineer taught him which components are most stressed. And once the correct combination of components is found, the results speak for themselves.
Follow along as we highlight the main reasons why certain parts were chosen when building this wild-yet-durable, force-inducted Pontiac. It may not be the type of engine every hobbyist can attain, especially given the presence of Ram Air V heads, but it's certainly radical enough to draw anyone's interest!
Special thanks to Lee Schwilm and Tom Vaught for their assistance.
1. In its current state of tune, this 397-cube Pontiac engine has produced an astonishing 780 rwhp at 6,800 rpm.
2. The 3,200-pound (race weight) '70 Trans Am that is home to this engine posted a best 11/48-mile pass of 6.20 at 115 mph in its shakedown run at VMP. Its transmission is a modified two-speed Powerglide automatic, and the rear axle is a custom-fabricated unit with a 9-inch Ford center and 4.10 gears.
3. Beginning from the top, the Vortech Engineering X-Trim centrifugal supercharger has a maximum rpm of 65,000, which is achieved by 7,000 engine rpm, and produces a maximum boost of 17 pounds in Lee's combination. Two modified bypass valves prevent the engine from over-boosting while decelerating. While the unit draws nearly 100 hp to operate, Lee's engine could crank out in excess of 1,100 hp. Teddy Houser Race Cars of Lincolnton, North Carolina, fabricated the supercharger induction tubing. The water-to-air intercooler was custom made by Travis Quillen of Huntsville, Alabama.
4. The intake manifold is a custom-made sheetmetal unit by Bill Fodder designed specifically for the R/A-V's unique intake ports. Travis Quillen created the upper plenum, installed fuel-injector bungs into each runner, fabricated the fuel rails, and installed an AccuFab 105mm throttle body and 160 lb/hr injectors.
5. An electric fuel pump from Weldon Pump in Oakwood Village, Ohio, pressurizes the fuel system to a regulated 39 psi. A standard Melling high-pressure oil pump distributes the refined crude throughout the engine.
6. The brain of the system is a FAST electronic fuel-injection unit. Travis Quillen performed the initial calibration, while CP Racing in Charlotte, North Carolina, is currently dialing in the combination on its dyno.
7. The crank-trigger ignition system is comprised of myriad MSD Ignition components, including a 7AL2 box.