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PostPosted: June 16, 2013, 7:26 pm 
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I thought this would best fit in this catagory instead of my build log. I have been trying to quiet my Locost down. In that effort, last year I purchased a pair of Harley Davidson Touring muflers. I recently purchased a sound meter for some testing. This last week, I went about fabricating a splitter to run the 2 mufflers in parallel. I thought that the flow would be a problem when used with my rotary engine.

Since today was Father's Day, SWMBO volunteered to be my test engineer. So here are the results of a day's worth of fabrication and a few hours of comparison testing. All cockpit measurements were taken in the center of the car, about head level and slightly forward of our heads so we could read the meter. Note that this is an eBay meter that cost ~12 bucks, so absolute levels may not be exact. However realtive numbers should be, well, relative.
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dBA.JPG
dBA.JPG [ 138.27 KiB | Viewed 3165 times ]


What I can see is that the Touring mufflers may be slightly quieter as measured from the street. However, internal to the cockpit, they are definitly louder. The difference in cockpit numbers are probably due to the different exhaust directions. The original muffler is directed low and away from the car. The Harley mufflers, due to their preconfigured condition, were pointed toward the rear fenders, slightly outward. My passenger/test engineer definitely noticed a difference in heat rolling into the car, much favoring the original setup. Heat conducted into the cockpit from the chassis rails were more noticable too with the Harley mufflers. She also noticed the Harley mufflers were louder to her.

I during the drive testing, I measured road noise by pushing in the clutch and coasting at idle ~45 MPH. Those readings were around 90dBA. That is road, tire and wind noise.

Just to check what would happen if I used just one muffler, while idling in the garage, I blocked the end or the lower muffler. There was no measurable noise difference. I then blocked the upper muffler, and there was an immediate 5dB reduction in noise. From that short test, I think that one of my mufflers are shot. If all other testing was positive, I would source another touring muffler and retest. I expect it would be quieter still, maybe by ~3dB. But I don't expect any heat difference. And we can't have any of that! Due to the passenger heat, the cockpit noise problem and the issues with redirecting the exhaust on the Harley mufflers, I don't think I'll continue any more tests. I don't care to spend another 50 bucks to get more mufflers for further testing just for you blokes. :boxing:

For comparative testing, I measured 15 random cars driving back and forth in the same setup as my 30MPH drive-by test. They measured from 61.6 to 77.6dBA and averaged 65.3dBA. Most of the noise was primarily tire noise by my estimate. My Locost averaged 85dBA! I guarantee that was exhaust noise.

Ask questions, comment away or take this test data and build on it. Your choice.

Happy driving.....

Attachment:
File comment: Perforated plate on original setup
perforated original.JPG
perforated original.JPG [ 24.89 KiB | Viewed 3165 times ]
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File comment: Original Heart Throb resonator and turbo muffler
rear original.JPG
rear original.JPG [ 53.81 KiB | Viewed 3165 times ]
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File comment: Touring mufflers
rear harley.JPG
rear harley.JPG [ 61.24 KiB | Viewed 3165 times ]
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File comment: Splitter. Note the blueing from the heat of the rotary exhaust .
harley splitter.JPG
harley splitter.JPG [ 40.95 KiB | Viewed 3165 times ]

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Last edited by rx7locost on October 7, 2017, 11:44 am, edited 1 time in total.

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PostPosted: June 16, 2013, 7:52 pm 
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Great info. I too have the Harley touring mufflers and a Miata exhaust option. I do really like the way the Harley exhaust look so I guess I will repeat your tests in about 6-12 month or longer depending on when I get the engine running.

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PostPosted: June 18, 2013, 9:43 am 
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Hi Chuck-
Good research work, Sir! I know rotaries have high exhaust temps, so I can see that heat making its way into the cabin being a problem, noise notwithstanding.

The Harley mufflers sure look sexy, but I bet that rear fender would need repainting or replacing real soon. :ack:
:cheers:

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PostPosted: June 18, 2013, 3:26 pm 
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trust me, i'm an engineer.

seriously though, if you could get that exhaust out the back, you would be a happier locoster.

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PostPosted: June 21, 2013, 6:43 pm 
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Thanks for testing. I bought a sound meter off Ebay that is probably identical to yours. I will be doing some testing also. I wonder if a rotary engines air intake is noisier too.

Since all the air flows through the center outlet, one could fit a 1-1/2" or so mandrel bend into the center and weld it on for a kick out, but it seems it is just as loud as the muffler you have.


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