Could it be flat-plane crank?
The Humbler: 1970 GTO’s vacuum-operated exhaust was ahead of its time
At the peak of the muscle car era, the 1970 Pontiac GTO offered an innovative driver-controlled exhaust that boosted performance—and ruffled feathers.
The Vacuum Operated Exhaust (VOE), initiated by a stealthy pull on a dash-mounted control, activated flaps on both mufflers that bypassed the stock exhaust routing and opened the gates to twice the sound and improved air flow. In concert with the Pontiac Ram Air induction system, the VOE delivered additional, measurable power. But it was pulled from the options list almost immediately as GM conformed to legal requirements in several states. (That was the official reason anyway. Unofficially, it was doomed by internal politics).
Pontiac motored into the ’70s with versions of its 400- and 455-cubic-inch V-8 engines that kicked out the jams with 350 or 370 horsepower in Ram Air IV trim. Pontiac performance was available across the lineup, but the driver-controlled, vacuum-actuated, dual-mode exhaust was exclusive to the GTO. For 1970, Pontiac referred to the GTO as the Humbler, suggesting that the collective power of Pontiac performance would humiliate drivers of lessor, so-called muscle cars. Even if option-code W-73 VOE was intended only for off-road use, corporate powers shelved it before “excessive humiliation” became a real problem, like in the one-and-only television commercial featuring the GTO VOE option.
Dual mode exhausts have American roots stretching back to at least the early days of gow jobs and hot rods. Cutouts, dumps, or lake pipes were the hot setup for hot rods that were driven on the street and then raced on Southern California dry lakebeds. After a long run from the city out to the lakebeds, enterprising drivers would uncork the exhaust by removing the few bolts holding their block-off plates. Reversing the procedure kept things quieter for the street. Later aftermarket versions of the setup incorporated high-zoot cable or electrically actuated cutout valves for universal installation, essentially making the Pontiac VOE a factory production version of hot rod and street-performance culture.
The system only made it onto about 240 ’70 Pontiacs, but the VOE was such a great idea that it lives on today. Modern versions of the system are commonplace, not just in contemporary muscle cars like the Chevrolet Camaro, Ford Mustang, and Dodge Challenger SRT Hellcat but in all shades of performance cars. Aftermarket manufacturers have also tooled up their own versions of the original Pontiac VOE setup, along with an array of similar systems for vintage and modern muscle cars. We only wish the GTO was still around to join the party.