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I tested resonance on what I believe is the most well known two stroke pipe, Gordon P Blair’s Grand Prix 125cc pipe. This 125cc road race pipe is in his book Design and Simulation of Two-Stroke Engines on page 444. All input data for this test matches Gordon Blair’s specifications. Rpm 11750 Exhaust duration 198 Exhaust gas temperature 600 degrees Celsius Tuned length 832 mm, total effective length calculated out to be 1181.5 mm After testing this pipe, it had very good resonance at 11750 rpm and 9315 rpm. The image is at peak power 11750 rpm.

This Banshee HQ thread is for HQ members that want to understand how two stroke pipes are designed using math. Anybody following this thread will learn how to design pipes and have the know how to compete with the top pipe builders, at the track and on the dyno. We will discuss what software to use, types of formulas to use and tricks we do to get an advantage. Tell your friends that Banshee HQ forum is the only place to get this information. Will post some technical stuff soon.

Awesome. id love to see what equipment (jigs etc) needed to make a pipe. Curious of templates and matching each side. thanks for starting this thread

Probably one of the most important aspects of pipe tuning, you’ve read my posts about tuning with effective lengths formulas. An example pipe will make it easier to understand. It takes .265 milliseconds for pressure waves to travel through a header section 47mm (avg) diameter by 200mm long. It also takes .265 milliseconds for pressure waves to travel through a belly section of 110mm diameter by 150mm long. The example pipe shows the header section pressure wave travels 50mm farther than it does in the belly section in the same amount of time. Using effective length formulas makes it very easy to time pressure changes in the pipe for resonance tuning. The end of each section will start a return wave to and from the exhaust port. Header and diffuser sections are tuned and timed to be in resonance with the last diffuser, belly and baffle.

I wouldn't cut the flywheel for that build, it should rev quick. If all I had was a lightened flywheel I would run it and see how it works.

I test all pipe designs with Mota two stroke simulation software. Mota shows the 4 diffuser, 3 diffuser and 2 diffuser pipe designs will make over 70 horsepower at the crankshaft per cylinder. The test engine was a 465 Cheetah Cub on gasoline. The dyno results on all three made just over 113 horsepower and 60 foot pounds of torque. These pipes were designed for the heavy rider (doughboy class), the tuned length was much longer than the average drag pipe. Designing a pipe around the chassis weight / riders weight helps the heavy rider like myself to launch without bogging.

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The three most important formulas for resonance tuning are heated speed of sound, tuned effective length and horn coefficient. (Heated speed of sound) this formula converts exhaust gas temperature to pressure wave velocity. (Tuned effective length) this formula converts true tuned length of each section to effective tuned length of each section. An example pipe with a total tuned length of 1000 mm may have a total effective length of 1400 mm. The effective length of each section gets longer as the diameter gets bigger. A tuned effective length of 1400 mm on this example pipe would be used to time and tune for resonance. (Horn coefficient) the kh factor controls diffuser angles for smooth and controlled expansion.

These three images are the same two diffuser pipe, it has resonance at 10150 rpm and 7772 rpm. At 6048 rpm the belly section return wave has no support from a diffuser section. Sections in the pipe not including the main wave from the baffle have two return waves tuned to be in resonance with the header or a diffuser section with 4 return waves. A three diffuser pipe has a diffuser section supporting the belly section!

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