Words by Richard Holdener
Making power with a big motor is easy; all you have to do is feed the displacement with head flow, cam timing, and a good induction system, and you are set. Making power with less displacement becomes more difficult, but, as this test clearly proves, not impossible.
The key to power extraction for the displacement challenge is obviously boost. There is no better equalizer for cubic inches than a little positive pressure. While adding boost to a stock motor will yield substantial benefits, adding power to a modified one is even better. The extra power offered by the heads, cam, or intake upgrade is actually multiplied by the available boost pressure. To illustrate the torque benefits of boost on a smaller motor, we decided to storm a Chevy 4.3L V-6.
The 4.3L V-6 was Chevrolet’s most successful V-6 platform, and for good reason. Though offering only six cylinders, the 4.3L shared considerable hardware with the small-block V-8. In essence, the 4.3L was a V-8 minus a pair of cylinders (3 and 6). Like the 350 Chevy, the 4.3L combined a 4.0-inch bore with a 3.48-inch stroke. The shared displacement facilitated parts interchange between the V-8 and V-6, including pistons.
Though the V6 utilized the same 5.7-inch rod length, the V-8 and V-6 rods differed in rod journal diameter (due to the 30-degree offset rod journals), and therefore did not interchange. However, the V-6 did share the bore spacing, deck height, and many valve train components with the V-8.
What this meant is that those shared components for the V-6 were readily available at affordable prices. It also meant that the V-6 received many of the upgrades applied to the V-8 over the years, including hydraulic roller cams, one-piece rear main seals, and even the much-praised Vortec cylinder heads.
Knowing the V-6 received the many upgrades, we chose accordingly for our build up. The test motor started out life as a 2002 4.3L from an Astro Van. The 2002 model featured not only the one-piece rear seal, hydraulic-roller valve train, and the high-flow Vortec heads, but also a dedicated balance shaft. Unlike V-8s, the V-6 design was inherently prone to vibration. Use of a balance shaft helped counter some of the unwanted vibration, making these later 4.3Ls much smoother in operation, especially if you plan elevated rpm in a performance application.
Though our V-6 was essentially a rebuild of the long-block components (with .030-over pistons), we did replace some of the factory components before adding boost. Naturally, we ditched the problematic fuel injection for simple and effective carburetion. The EFI intake was replaced by an Edelbrock Performer intake and matching 500 cfm Thunder-Series carburetor. The carbureted induction system required replacement of the computer-controlled distributor with a conventional unit from MSD.
Once the V-6 was topped with carburetion, we took a look inside the motor, more specifically to the cam timing. Naturally, the factory cam timing was purposely mild, and ill-suited to our needs. If you want to find out just how much power our cam was worth, check out the story “The Missing Link” in Power & Performance News. The stock cam was replaced with a COMP 280HR grind that offered .525 lift, 224-degrees of duration (at .050), and a 110-degree lsa. The 280 cam was a solid step up the performance ladder, but could hardly be considered a full (or even 3/4) race grind.
The cam was teamed with a new set of hydraulic roller lifters from COMP Cams. The hydraulic roller valvetrain was one of the many benefits of using this later 4.3L configuration, as it allowed for more aggressive cam profiles (only possible with a roller follower). The 2002 V6 also featured roller-fulcrum rockers (not unlike an LS V-8), but we did upgrade the stock valve springs on the Vortech heads with a set of 26915 beehives, also from COMP Cams.
A set of long-tube headers was the only missing performance ingredient, but run in anger with the stock exhaust manifolds, the carbureted and cammed 4.3L produced 251 hp and 298 lb-ft of torque. Now it was time for boost!
Boost for our V-6 was supplied by a TorqStorm centrifugal supercharger originally designed for a small-block V-8. The 4.3L shared many of the accessories and water pump mounts with the V-8, so the TorqStorm kit bolted right in place. Since the kit’s designed to blow through a carburetor using the supplied carb bonnet, we opted to replace the Edelbrock carb for a Carb Solutions Unlimited unit designed for boost.
The combination of metering block modifications, available jetting and adjustable (boost-referenced) power valves allowed us to dial in the air/fuel mixture under the rising boost curve supplied by the TorqStorm supercharger. The supercharger kit was supplied with an 8-inch crank pulley and 3.25-inch blower pulley.
This produced a peak boost reading on our V-6 of 13.3 psi at 5,800 rpm, though there was plenty more boost and power left on the table. We comfortably exceeded 620 hp on a 5.0L V-8 application using this exact blower and pulley configuration, so the sky is the limit if you built a serious V-6 to handle the extra boost. All dialed in, the TorqStorm supercharged V-6 produced 460 hp (459.8 to be exact) at 5,800 rpm and 423 lb-ft of torque.
Sources: COMP Cams, compcams.com; CSU, csucarbs.com; Edelbrock, edelbrock.com; Holley, holley.com; Lucas Oil, lucasoil.com; MSD, msdignition.com; Speedmaster, speedmaster79.com; TorqStorm, torqstorm.com