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continues: H-pipe, X-pipe, 1, 2, 3...
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through each pipe rather than taking the 90-degree turn through the H-pipe into the other half of the system. In an X-pipe system, however, where the two sides of the system intersect, the gasses have no choice but to intermingle as they pass through the junction. This promotes improved scavenging effects by smoothing out uneven exhaust pulses from the engine's firing order. It also helps quiet down the exhaust, resulting in a mellower, less raspy tone. According to MagnaFlow, the faster acceleration of the gasses through an X-pipe causes them to flow in a linear fashion parallel to the walls of the tubing rather than tumbling. This "laminar" flowing gas is much quieter than tumbling gas, resulting in an exhaust tone up to 8 decibels quieter than a traditional H-pipe.
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Think of the port shapes of a cylinder head when you look at the internal surfaces of MagnaFlow's stamped X-pipe. The smooth radiuses and transitions contribute to airflow just like a well-designed short-side radius or a good valve job (in fact, its designer says the shape was inspired by the ports in a Dart Big Chief Pro Stock head!). MagnaFlow's universal X-pipe (PN 10789) is designed for 2-1/2-inch tubing in and out. For our system, they split the exit side open to accommodate the larger 3-inch pipe.
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 To standardize airflow on its SuperFlow bench, MagnaFlow flows mufflers through a 1.875-inch orifice the maximum size that will allow the bench's electric motor to produce 28 inches of water depression, which is the same standard used to flow cylinder heads. This is smaller than most people would use on a performance exhaust system, but it standardizes the playing field. MagnaFlow's 3-inch center inlet/offset outlet PN 14229 muffler as used on our system flows about 250 cfm at the standard depression on this bench. For comparison, the generic 2-1/2-inch mufflers we used with our smaller system flowed a mere 215 cfm, hence the cork effect.
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Every muffler manufacturer offers various combinations of inlet/outlet configurations to fit various requirements. What we didn't know is that these different combinations affect both sound levels and airflow. These MagnaFlow mufflers are arranged from left to right in order of highest flow and loudest sound level; center/center, parallel offset, center/offset, staggered/offset. The variation in flow from best to worst is only about 10 cfm, so this isn't a big issue.
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Prior to having a permanent exhaust system built, we finally got around to swapping the correct headers into our Mustang. When we originally slapped the car together, the 1-3/4-inch primary long-tube BBK headers we wanted to use were out of stock, so we borrowed a set of BBK's 351 Windsor swap headers from a friend. They use the same primary tube diameter but hang about an inch lower to accommodate the 351's wider block. They didn't really fit on our 302, so we lived with a nasty exhaust leak until we finally got our hands on the right pair. Fitment is excellent, and the extra-thick flanges contribute to good sealing. They're available in chrome or with ceramic coating for longevity.
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