Exhaust System Upgrade - What A Drag, Part 5

An improved exhaust system can radically improve your car's performance

Dan Foley May 11, 2012 0 Comment(s)
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Last month, we tuned the 950 Proform carburetor that resides on top of the Dart 509 in our '72 Nova SS. We swapped the fuel jets and air bleeds, added a 1-inch, 4-hole tapered spacer and a taller air cleaner, and switched from a solid lid to a breathable air cleaner lid. All the changes helped us to obtain an optimal air fuel (A/F) mixture ratio of 12.7 to 13.1 during the pull and 13.5 while cruising on the dyno.

Besides maximizing safe engine power output, this also helped to lessen the odds of engine-damaging detonation. That carburetor tuning session resulted in peak gains of 15 horsepower and 18 lb-ft torque to the wheels. At the go pedal, it felt like we gained more--it showed up in the average gains during the dyno pull from 2,500 to 6,400 rpm, where the 509 realized 24 average rwhp improvement.

After success on the induction side, it was time to move on to the exhaust. Our Nova was set up for a big-block when we purchased it, but the exhaust system left a lot to be desired. The dual exhaust on the Nova was 3-inch compression-bent pipes with 3-inch mufflers installed at the typical exhaust shop. Remarkable for this day and age, there was no crossover pipe, neither H- nor X-shaped. It sounded mean and nasty but was giving up power compared to a mandrel-bent exhaust with a crossover. A free-flowing, mandrel-bent exhaust with an X-shaped crossover would help us toward our goal of building a docile, 10-second, pump-gas street machine.

Rather than fab a system from scratch, we turned to the folks at Ground Up Restoration Supply, who supplied us with a Pypes 3-inch X-shape crossover kit, including Pypes' best-flowing Race Pro mufflers. From experience, we knew a mandrel-bent X-pipe exhaust system would deliver added throttle response, fuel efficiency, and power, with lower e.t.'s and decibels. The question was how much.

Once again, Matt Haufe and his crew at Tune Time Performance in Toms River, New Jersey, offered their shop and Mustang chassis dyno to help us get it all done. For our 30-mile ride there, we brought along our trusty decibel meter, carburetor jets, and air bleeds. It's always a good idea to be prepared to retune when making any changes, even an exhaust swap like this. Follow along to see how breathing easier can add more muscle to your super Chevy.

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