Post-Collector Exhaust Add-Ons Can Affect Exhaust Tuning

We’ve previously discussed header design; what about post-collector extensions? Most commonly seen on motorcycles and other small motors that are inherently peaky, a megaphone-shaped collector extension, in theory, can be beneficial on any engine because it further extends the system’s tuning range by delaying the reflected wave. As for straight collector extensions, they’re an old racer’s trick, an example of real-world cut and try. During initial tuning, a slightly long extension is installed, with a stripe painted down its length. After several runs, the collector is cut short to match the point where the paint stops burning off.

Although collectors basically act as transition pieces, extensions and megaphones serve to increase the system’s total effective length. This may cause the header to tune at a lower rpm than desired. To compensate, some experts recommend shortening the primary tubes by about half the length of any extension.

On a street car, the entire exhaust system acts like a giant extension, yet it’s rarely considered when designing an overall header system. Mufflers introduce yet another wild card, often significantly affecting the system’s wave-reduction properties. Still, most tuners try to optimize the combination’s performance without an exhaust system, hoping that any additional exhaust pipe and mufflers won’t screw things up too badly. Flowmaster is one high-perf muffler that claims to take into account reflected-wave theory and its effect on overall engine scavenging.

Contact

Flowmaster Mufflers
Santa Rosa, CA
707.544.4761
FlowmasterMufflers.com

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