You may recognize our '57 Chevy 210 named Project X from the 44 years it's been PHR's project car. It's been through many changes over the years, and you might remember last year it received GM Performance Part's prototype ZL1 all-aluminum big-block 427 crate motor, celebrating the baddest engine option of 1969.
While Project X was under the knife for its total makeover, GM Performance Division decided to incorporate Quick Time Performance's electronic cutouts into the exhaust system. The simplest way to install these in your own ride is to graft a Y-pipe in behind the header, and bolt the cutout to one end. Project X got a slightly different installation because of its unique body-mounted exhaust exit.
We were all witness to the audible effect the cutouts have on the ear, but now it's time to see what it really does for performance. Releasing the exhaust so early in the system reduces backpressure and allows the engine to breathe, so we expect it to perform differently when the cutouts are opened. Simple drive tests aren't conclusive, especially because the intense sound of the car can distract you from what the seat is telling you. We strapped the '57 to our Mustang chassis dyno, and did a pull with the exhaust directed though its mufflers, and one with the cutout valves opened, directing the exhaust out before the mufflers and tailpipes.
Our results showed almost no change to peak horsepower and torque, but we did find other notable changes. The lack of restriction in the exhaust system yielded horsepower and torque increases in the low- and high-rpm ranges, and showed a slight loss in the midrange. These cutouts are definitely cool, and make more power most of the time, so why not have a little fun with them?