Frank. You’re absolutely right in that the mufflers in the various tests using the EMC headers are essentially collector extensions from a design point of view. I’ll add that on the drag cars I’ll use a 45° cut on the collector outlets which has always proven to be a benefit. On the EMC engine itself, I was using ~8' of additional 3½" tubing behind each muffler as part of the tuneup on that engine. Torque curve saw a drastic shift when the extra pipe was added. When the extensive exhaust test on the +060 312 dyno mule is performed, I’ll include a variety of 3½” diameter extensions on the EMC headers just for the additional information it will generate. A general statement on exhaust testing performed thus far is that each engine combination requires a different setup on the exhaust to insure optimum engine performance. The testing on the dyno mule will give some generic guidelines but as is already evident in using the EMC headers on several different engines, the torque bands vary depending upon the total engine combination.
Here’s the pic of the EMC headers and mufflers that are being used.
EMC Headers – 1¾ X 1 7/8” stepped tubes with 3” merge collectors installed within the 3½” collector shells. The Magnaflow mufflers are 3½” I.D. and add 18” to the current collector length.

Lorena, Texas (South of Waco)