Our subject for this experiment, a Rat-powered '69 Z/28, started out with a wasted exhaust system.
The mufflers had touched down at least once, the packing long gone. The tailpipes had also been hacked off, givng the exhaust note a gargling, raspy tone. We responded by installing one of MagnaFlow's new American Muscle crossmember-back systems. The exhaust note grew sharper and cleaner, taking on a growling sense of urgency the discarded pipes lacked. The veteran Z sounded leaner and meaner--and leaner was just what this ride needed.
Looking to reduce backpressure without sacrificing exhaust gas velocity, MagnaFlow's Richard Waitas picked a 2.5-inch setup for this mild-396-powered F-body. So just how much was flow improved? According to readings during our pre-install pull on MagnaFlow's Dynojet chassis dyno, this fat-block was running rich, registering an air/fuel ratio of 11.5:1. With the new tubes in place, our mixture was almost a half point leaner, checking in at 11.1:1. Accordingly, we picked up 13.5 hp and 14 lb-ft--with more to be had. "This car could stand to lean out to 12.0-12.5," Waitas told us. "Typically a solid 1-point change would be good for another 5-10 rear-wheel horsepower in a big-block Chevy."
The whole job only took half a day, and MagnaFlow recommends that a professional install its products, but a layman who can handle a bit of welding can do the job. Either way, the payoff-- both to the ears and at the pedal--is well worth the effort.