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Dream Pipes - Chevy High Performance

MagnaFlow's American Thunder Exhaust for Early F-bodies

John Nelson Apr 28, 2006

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.


Scary as this may sound, our ace installer, MagnaFlow's Jim Gose, figured this '69 Z/28 had seen four or five exhaust systems in its day... which means this ratty mess actually replaced something else. The 2.25-inch tubes, battered mufflers, and lack of tailpipes kept the swapped-in 396 from fully exhaling.

After supporting the outgoing exhaust with stands, Gose made quick work of the muffler straps.

These collectors were unusually welded to the pipes, so our man broke out the reciprocating saw. Thinking ahead, Gose left a piece of the old pipe in place. Hopefully you'll only have to unbolt a flange connector.

With the old exhaust system history, it was time to contemplate the new. The American Muscle system features MagnaFlow's Tru-X crossover. This assembly balances the exhaust gas pulses between the two sides of the system and promotes better flow. The result: better sound and more power.

MagnaFlow's mufflers use a straight-through design to minimize exhaust restriction. The kit comes with all necessary mounting hardware--and a set of sorely needed tailpipes.

Gose set the system in place for a mock fitment, beginning with the mufflers. This '69 started life as a dual-exhaust car, so it has threaded bolt holes for the original muffler hangers. A single-exhaust car should have one set of holes, along with a pair of dimples on the opposing side.

The new hangers matched right up to the OEM mounting location. If your vehicle doesn't have suitable bolt holes to accommodate the hangers, you'll have to set the entire system in place, determine where the muffler hangers need to be, and drill the appropriate bolt holes. MagnaFlow provides the bolts.

The plastic connector snaps into place on the frame hanger (it's a snug fit--a little penetrating oil may be needed), and the muffler hanger snaps into the other end.

Gose continued forward, fitting the X-collector onto the mufflers. The directions call for at least 1/2-inch clearance between the exhaust components and any other parts, especially those that move (like the driveshaft).

With the crossover tucked into place, we moved on to the extension pipes. After sliding them onto the X-pipe, Gose lined up the extensions up with the small piece of old pipe still attached to the headers, marked his spot, and made the cut.

This clean connection is what we ended up with. In header applications that use a three-bolt flange mount, you'll need to bolt a flange extension to the headers then cut the extension pipes to the appropriate length.

Quick Notes

Install and dyno-run MagnaFlow's American Muscle crossmember-back exhaust system on a 1969 Camaro

9.5:1 396ci big-block running an Edelbrock Performer intake, Holley 750-cfm carb, Hedman headers, and a mild Lunati cam

The kit is approximately $600


MagnaFlow Performance Exhaust
Rancho Santa Margarita, CA 92688

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