1970 Fairlane - Magnaflow Exhaust - The Twister Going With The Flow - PHR Project Car Part 5

Nothing on Earth sounds better to a gearhead than an uncorked open-header engine. It's the sound of power, the thumping racket that makes you tingle all over. Unfortunately, if you want to drive on the street, that octane-fueled mechanical music needs to be knocked down a few decibels to satisfy the local constabulary. But silencing the beast under your hood doesn't have to put serious hurt on the power getting to the wheels. By selecting the right exhaust system, you can have the best of both worlds.

Our '70 Fairlane is offbeat-cool, but thinking outside of the box has a price. That price is that it's hard, or impossible, to find vehicle-specific performance parts. Everybody makes stuff for 69 Camaros, but when we looked foran off-the-shelf exhaust system for our Fairlane, we were greeted by the sound of crickets. This meant going custom. The folks at MagnaFlow had just the right parts in stock to build a system that would sound great without robbing power from the 552hp small-block residing under the hood.

The decision was what size and type of system to install. Should it be 2.5- or 3-inch? Should it run all the way back or end after the mufflers? Is an X-pipe worth the extra coin? MagnaFlow does this for a living, and we decided to pick their brains to see where we would get the most performance benefit.

Regarding pipe diameter, Richard Waitas, engineering director for MagnaFlow, told us: "In choosing between a 3- and 2.5-inch exhaust for a dual-role street/strip car, considerations in sizing are not purely based on peak power. In a race application, it is easy to build an exhaust that will permit max cfm flow at peak horsepower rpm. In an all-out strip car with a high-stall converter and airflow ranged toward high rpm, the larger-diameter system will definitely shine, but this is only the case in an application where the powertrain is designed for peak performance. Determining where your application fits most should sway you from smaller to larger. In a more street or street/strip application, consideration for the rest of the curve should be made, as power delivery 'feel' will be substantially different. This feel is often the difference in torque or midrange horsepower. Some of this midrange power and low-rpm torque is more desirable in a daily driven car, and sacrificing five to six peak horsepower for the same amount in the midrange will make the power more useable. In looking at flow capacities of the two diameters in a dual-exhaust configuration, the transition point where the benefit of a 3-inch versus 2.5- inch exhaust start to drift apart is near the 400-450hp mark. At this point, the horsepower and torque variations become more substantial, and the loss and gain needs to be more carefully analyzed."

Since our initial goal is to get the Fairlane into the 11s, we decided a three-inch system would work better with our single-plane Victor Jr. intake. We also asked Richard about the need to run an X-pipe. "The X-pipe is an integral part of our design. The X-pipe has been around for a long time; however, many people only know it as something NASCAR uses or as a 'crossover' pipe. The X-pipe, or as we call it, the TRU-X, increases the efficiency of the exhaust system using scavenging. Scavenging is a means of using existing exhaust pulse energy to enhance total flow. To maximize the output of our TRU-X, it should be placed where it can utilize the high-speed gasses expelled from the engine at a point where the vacuum charge created as the exhaust pulse crosses the X can create a pressure drop to a bank of cylinders or individual cylinder in its exhaust stroke. The engine can more efficiently expel spent exhaust gasses, making for greater cylinder filling, which equates to more power."

With a plan in place, we trailered the Fairlane over to MagnaFlow's R&D center so they could tame the raucous sound from our 408 and help us get another step closer to hitting the track.