Dynomometer (dyno) Muffler Exhaust System Part 2

Our 55 gallon drum for the dyno muffler has been modified with a 4 inch inlet at the bottom, provisions for feet, and necessary in this drums case the top has been cut off. Now the drum is ready for some sound deadening exhaust packing. Because the drum is such a large diameter compared to what a normal muffler would be we have a lot of room for material which should ultimately help keep the noise down. I needed to get this project completed quite so I could continue product testing our RZR Turbo Velocity Intake system, and also had a RZR 900 S coming in for a new intake design and pwrtuneECU tuning.


Not really sure how well this entire project will work out, initially I did not want to use a large amount of expensive exhaust packing to fill the drum.  I have several large rolls of BGF techmat high quality exhaust packing at the shop, but filling the drum would require two entire rolls and if the drum muffler did not work out the packing would be useless. So instead I decided to fill with pink home insulation from home depot on the outermost edges, and I would use one layer of real exhaust packing on the inside that would contact the perforated core. I started with a small square of insulation at the bottom (see pic) and about half of a roll of the unfaced pink insulation placed that I placed into the drum filling the bottom half of the space. I carefully put an inner layer of the white exhaust packing inside that so the half the drum was packed. Then I inserted the perforated core before I filled up the rest of the drums. It didn’t look like I could fill up the drum and then put the core in, nor did it look like I could put in the core and then fill the drum, so I did half and half. The inner perforated core that I used I also got from home depot, it was a 40”x40” sheet of aluminum about 22ga. covered in triangular holes.  Normally for a muffler the holes in the core would have been too large allowing most of the exhaust packing to easily escape. But since the muffler core it would start at a bottom 4” diameter and taper up to an 8” I didn’t see the packing easily escaping running at max 1000cc Polaris RZR UTV motors. We on our dyno we run.


I finished the packing with the pink insulation on the inside and one layer of exhaust packing on the inside, you can see from the two pics the packing with core sticking out. Next I cut a hole in the drum lid and used an HVAC 8” starter take off for the outlet. Placing the lid on the drum the muffler core came into the 8” take off about 2” just enough to secure of with some high temp tape. The 55 gallon drum has now been converted into a dyno muffler with a 4” inlet at the bottom and 8” outlet on the top. The last thing I wanted to do was install a fan at the outlet to help keep the back pressure down and then will be ready to test.


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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.


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.


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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