In my days as a rocket scientist designing the R-4D-16 dual mode rocket engine for JPL there were all kinds of challenges in ensuring the performance and reliability of the rocket engines.
One of the greatest challenges was designing an injector to produce smooth and stable combustion of the fuel and oxidizer in the combustion chamber. There were occasionally these acoustic instabilities (tangential modes) in the combustion chamber that could be excited and start a run away condition that could quickly destroy the engine. To address this problem I used Helmholtz resonators inside the rocket engine to damp out the acoustic tangential modes. A tangential mode is basically a shockwave that would spin around the inner circumference of the combustion chamber analogous to a supersonic tornado at 20K Hz. Not unlike detonation, this tangential mode would scrub off the boundary layer, radically increase the heat transfer into the chamber walls and result in a catastrophic failure.
Helmholtz resonators were the solution to these tangential waves. By properly tuning the Helmholtz resonator to the frequency of the tangential mode you could either magnify or eliminate the shockwave.
These can be used on a fully modified exhaust system to make additional power. Traditionally, if you already have an intake mod, headers, test pipes with a full catback exhaust and tune, that was the end of the line. There was no more left to gain. ...But not any more.
This is Motordyne's debut of the patent pending Advanced Resonance Tuning (TM)
They're not headers. They're not conventional test pipes. They're ART pipes!
The plot below is without exhaust cam phase tuning. The ART pipes respond very well to cam tuning.
Regular test pipes always result in a large loss of low end torque. Compared to test pipes, the ART pipes produce a large gain in low end torque that is clearly felt and can be very usable for auto-cross or powerful launches in drag racing.
The plot below is a Horse Power comparison of ART pipes Vs Stock catalytic converters.
The plot below is a Torque comparison of ART pipes Vs Stock catalytic converters.
Although these ART pipes are designed and tuned for power they greatly reduce rasp, drone and loudness.