Dynomometer (dyno) Muffler Exhaust System Part 1

Recently we had a noise issue at our pwrtune shop. Earlier this year we purchased a Dobeck Performance Axis RX-74 chassis dyno. This tool is essential to tuning with fuel controllers and doing ecutuning and flashing. Being able to maximize performance and drivability with performance exhaust and velocity intake systems on an actual dyno measuring real world horsepower is critical. And let’s face it, going wide open throttle watching power numbers climb driving on the dyno is a lot of fun.
Dyno Drum Muffler Materials.JPG
 
We were running Polaris RZR’s and other powersports vehicles on our new chassis dyno and forgot that the noise might be an issue with the neighbors. Our dyno sits in an end bay with a single vehicle door. With the door open running a 2016 Polaris Turbo RZR and one of our prototype exhaust systems I measured the db level outside at around 117db. Ouch, I really hadn’t noticed that the noise was that bad, but of course I was always wearing ear protection because the noise was so bad. Inadvertently we pissed our neighbors off for a couple months and something had to change going forward.
 
To address the sound issue I set out to construct a large muffler out of a 55 gallon steel drum that I would use to run the dyno vehicle exhaust through. Using an updraft exhaust fan at the outlet to reduce backpressure I basically wanted to make a very large muffler that would quiet down the sound of a UTV running full throttle at 90 miles per hour. And I wanted to have the ability to shut the door and run test completely inside our shop. Overall my goal was to reduce the db levels to something around mowing the lawn with a riding lawn mower. And after the neighbors had threatened legal action over the noise I was in a pretty big hurry to get this fix built and implemented.
 
4 inch inlet at bottom.JPG
 
You can see from the pics below the materials I started out with.  I had a 55 gallon drum lying around so that was no cost. However it did have a sealed lid so not only did I have to purchase a lid but I also had to cut the drum open. To cut the drum open I saw on YouTube a guy use a pneumatic chisel and sure enough it was easy and took less than a couple minutes. After cutting the top off I had to make an inlet for the exhaust to come in. I decided to go with a 4 inch inlet that I would run 4 inch flexible to from the vehicle into the drum muffler. At the bottom of the drum I cut a 4 inch hole, inserted a 90 degree mandrel bent exhaust elbow, and welded in place all around the tube. Now the modified drum is ready to be packed with sound deadening material around a metal perforated core.
 

 

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