Very good info. It's a shame this stuff doesn't work with a dual exit exhaust.

 

Cool tuning! Thx for sharing.
I haven’t sat down with my calculator to figure out what the stock length Helmholtz resonator Hz was tuned for. I take it was to reduce some higher frequency tinny raw sounds to make it deep rumble more? What has your numbers shown?

I had mine too short at first and went further into the possible length and it lowered the total volume considerably and made it more mellow sounding. It’s lower but I still have boominess in the 2800-3000 range. I might be able to slide the resonator a bit more length without mods.

 

Sorry to disappoint, but the extent of math I've done on this is "hmm, the drone gets better if I make the chamber sit farther from the main exhaust pipe...what if I made it sit EVEN FARTHER?"

This makes it even mellower, maybe even too mellow now that I've spent some time with it. Might try an 8" pipe next.

 

I did this months ago with the Perrin helmholtz welded onto my Perrin dual exit catback. Mine is adjustable length wise however; needed 13" to properly cancel from 85-95hz (the low frequency boom). But yes, it unfortunately does reduce the overall volume of the exhaust, and the longer the connector pipe is the less volume required to properly work.

There is an app for measuring the proper frequencies to cancel as well as a spreadsheet you can use to get all the proper dimensions: Drone Reduction - Wilhelm Raceworks, LLC

Very good info. It's a shame this stuff doesn't work with a dual exit exhaust.

I literally did it and its perfect lol.

 

I did this months ago with the Perrin helmholtz welded onto my Perrin dual exit catback. Mine is adjustable length wise however; needed 13" to properly cancel from 85-95hz (the low frequency boom). But yes, it unfortunately does reduce the overall volume of the exhaust, and the longer the connector pipe is the less volume required to properly work.

There is an app for measuring the proper frequencies to cancel as well as a spreadsheet you can use to get all the proper dimensions: Drone Reduction - Wilhelm Raceworks, LLC




I literally did it and its perfect lol.

This is an amazing article, thanks for posting!

 

Welcome

Mine was originally 6" connector pipe because I didn't have extra pipe around, and that did cut some drone especially when the car was cold, but the drone would return as the car warmed up. This was because drone is based on frequency and speed of sound which change with the temp of the resonator itself (I used the figure in that article, iirc like 110F as my match for ideal balance). That's when I stopped messing around and used the spreadsheet, and that killed it instantly as expected (science/math will do that).

 

Actually, it's not raining today so yeah I'll try to snap a few in a bit.

 

 

Who did you use to do this? It looks clean.

 

I bought the Perrin axleback and stole the helmholtz/clamp off of it, which is like 75% of the work. The rest was just like 10" of 2.25" SS straight pipe to extend the total length (adjustable 12-14.5" iirc). Drill a 2.25" hole with a hole saw and shape the pipe to match the catback pipe curve on the one side, and weld it all up. I then gave the axleback to my buddy doing the welding and paid for dinner to cover the modification.

You could also create the whole thing, but that's a lot more welding, and I dont weld, my buddy does (as said)...

Killed all the drone, but also made the system a bit quieter overall (I'd say roughly 25%). So either need to add a front pipe or headers to get some of the volume back.

 

Could packing be added to that "muffler" to help reduce the drone?

 

Absolutely ^

My question would be why? The stock front pipe is resonated and the stock catback has a bottle-type resonator. But in any case, you could swap the bottle type for a longer and/or larger diameter one or possibly be able to add a Helmholtz (would just have to be long and thin to fit in tunnel).




Generally speaking, packing reduces volume across the spectrum versus cancelling specific frequencies. So, the drone would likely be less but so would everything else, therefore the resonator is far more ideal IMO.

 

Maybe this would be a good place to ask this since you're all modding your exhausts:

In the stock exhaust, is there some way to add another resonator somewhere in the catback?