Daily Archives: March 7, 2019

Take cover, I’ve been thinking again

I have been thinking about the Sprint-T again. Specifically thinking about that super muffler that will require I drill hundreds if not thousands of holes for exhaust pulses to pass through so the gas flow is not impeded by shock waves, like the walls of a supersonic wind tunnel. And doing some research on those tells me that if this muffler is long enough I don’t need to use any absorption material between the core and the shell, just a bit of empty space to let the sound pulses bounce around and dissipate. Now exactly how much empty space is “enough” may require some experimentation.

The thought of running experiments for not enough, just right, and too much empty space has me slightly excited. After all, this is the Holy Grail for street performance, and more than a few race tracks. A muffler that is both quiet and doesn’t choke the engine down at higher RPM is seriously sought after, especially if it lasts at least as long as the straight pipe it would be replacing. Now the down side of this would be the problems in mass producing the core. Obviously doing it the way I’m going to, drilling holes in a tube by hand, just ain’t going to fly. Other ways could be a CNC machine that drilled holes in a tube, welding perforated sheet as a tube, forming perf sheet into a flanged half tube and then welding or using screws to make the half tubes into whole tubes, or some other method I haven’t thought about yet. And a quick Google search showed there are companies making perforated tubing to order in whatever diameter or wall thickness I can imagine. But anyway the experiment for me requires making the core then attaching the outer housing some way that centers the core and makes sure it stays centered, and making the same core fit different sized housings to see which one makes the engine quiet without packing material. That one I already have figured out, make toruses with the inner diameter the same as the OD of the core, and the OD the same as the ID of the housing. Most of the rings would be tack or skip welded to the core to keep them in place as the core is inserted into the housing but the ends would get fully welded to prevent noisy leaks…

And after building one would get installed as a control on one side of the engine, while the rest are installed on the other side for comparison, with both getting measured so if the sound level changes I can be sure it isn’t because of changing conditions, and if conditions change use the control muffler to normalize the test results. Now if I had unlimited test resources I would test things like if the space between the centering rings changed the results, how much changing the diameter of the housing compared to the core changed the sound, and if there was an optimum length for the housing beyond which the noise level didn’t go down, that kind of interesting stuff that can only be determined by cut and try or by using a supercomputer to model the gas flow. And three guesses what I don’t have access to here at Casa de El Poeta, first two don’t count because there are only two choices. With what I have now my experiments are limited to outer housing diameter and length, after I get an engine to test them on…

And it looks like I have typed enough tonight, this should hold your imaginations for a while, while I think some more.