David Hoffman's performance-tuned '70 Coronet R/T didn't have the edge or the sound he wanted, and a quick backpressure check revealed that the exhaust system was not doing its job. He first noticed something was amiss after a buddy remarked that the exhaust seemed to have a choked, wheezing sound compared to other 440s he'd been in. On closer inspection, Hoffman found that the system-a basic Chrysler dual-exhaust system using compression-bent tubing, factory Hemi mufflers, and 211/42-inch compression-bent tailpipes-looked fine, but the pipe diameter was constricted to 211/44 inches in the over-axle pipes.
By chance, Hoffman got in touch with the experts at Flowmaster just when they were looking for a B-body Mopar to test-fit a production version of their new Delta Force 3-inch exhaust system. Hoffman really wanted to get it right, so he opted to install a set of TTI 171/48-inch headers with 3-inch collectors at the same time. The crew at Flowmaster was confident they could create a truly pleasing exhaust tone as well as some really impressive numbers on his already healthy 440.
The idea was to baseline the 440 on Flowmaster's chassis dyno, install the new Flowmaster 3-inch B-body performance exhaust and headers, and then dyno it again. To kick off the process, the dyno team strapped the B-body onto their new SuperFlow SF-840 chassis dyno. This rolling road is an inertia-weight dyno used in conjunction with eddy-current brakes. It offers accurate testing of acceleration, step testing, steady state, full-throttle, and coast-down.
Baseline-testing the original system tallied results of 289 hp and 365 lb-ft of torque. With that accomplished, Flowmaster put the R/T on the hoist and began installation of the new 3-inch Delta Force exhaust system.
Lee Thompson, head of Flowmaster's R&D shop, prototyped this B-body system, and the quality work shows up in how easily the 3-inch system installs on header-equipped powertrains. Engines without headers need an extra custom head pipe to complete the installation.
It took Lee about two hours to remove the old pipes and fit the new 3-inch system. The installation requires only a basic set of handtools, although a Sawzall is handy for the removal of the old system. During the installation, Thompson hangs the entire system first before tightening any connections. He constantly uses his steel tape measure to check alignments, keep a minimum of 31/44 inch of clearance around all components, and ensure that the tailpipes emerge at the right angle and extension.
The new Delta Force B-body 3-inch kit (PN 17382) comes with step-by-step instructions and all-new hangers and clamps. Once Thompson had rechecked all the clearances and tightened the clamps, he performed a final check of the system's alignment. Once that was complete, the system was ready to be fully welded to complete the job. If you don't have a welder, you can fit the system at home and have a muffler shop do the installation, or just have the shop do the finish welding after you've done the fitment.
Once Hoffman's system was in place, the Coronet was given a quick testdrive and then put back on the chassis dyno. Hoffman could immediately hear the difference. The sound quality was far more pleasing than the wheezy, constricted tone it had before.
Flowmaster's Dyno Manager Kevin McClelland brought the Coronet up to temperature, and without tuning tweaks, the engine instantly ran stronger, pushing the peak horsepower to 341, up a massive 52 hp. At the very top, the horsepower gain jumped a resounding 58 hp. The torque increased an equally amazing 41 lb-ft to 404. These are truly impressive numbers, considering Flowmaster simply reconfigured the exhaust so the 440 could breathe correctly. According to McClelland, this 440 could have easily added another a handful of horsepower with some carburetor and ignition work.