Homemade J pipes/ helmholtz resonator

Discussion on fuel delivery & intake/exhaust tech & mods.
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bumpc723
Posts: 7
Joined: Sun Apr 18, 2021 12:48 pm

Homemade J pipes/ helmholtz resonator

Post by bumpc723 »

Just wanted to share some success for anyone interested in reducing exhaust drone.

My car has stock manifolds, primary cats, and the stock x muffler. LS9 cam and no DOD. The drone noise at 2,000rpm was unbearable.

https://m.youtube.com/watch?v=z5SY5oUTEcc

This guy has a good explanation to the science and calculations behind a 1/4 wave resonator and he also gives a link to a table you can use to find your required pipe length. It’s thorough but long winded. Basically you just need to measure average exhaust temperature and drone frequency. I used an IR temp gun and an app called Decibel X to measure the freq at 2,000rpm. Then you plug those numbers into his table and it gives you the length of pipe you need. You should use a bit smaller diameter pipe than the exhaust pipe you’ll be connecting to.

I measured 200F and 125hz so I want with 30.5” pipes. I added butt clamps to offer some adjustability. My tailpipes are 2.5” diameter so I used 2” for the j pipes. They fit really nice where the big rear mufflers used to be. For less than $100 I’m really happy with the results. I’d say my drone at 2,000rpm is 90% gone.
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Mooseman
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Location: Ottawa, ON Canada
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Re: Homemade J pipes/ helmholtz resonator

Post by Mooseman »

I had looked at those when researching exhaust systems and I'm thinking of adding them to mine. I also get a drone at around the same RPM. It's not super annoying but it's still there. I may add them to my system but I have bigger problems to deal with at the moment (tranny issues).
2011 Caprice PPV, former RCMP test vehicle, never put into service
Build Thread: http://www.newcaprice.com/forum/viewtopic.php?t=2419
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