[st3_casey]

I built a 3.5 inch cat back with a 3 inch catless downpipe all in my garage with pie cuts no bending. after about two weeks i had to order a resonator as the drone was awful. as it sits right now its a straight pipe with a vibrant 18" resonator and the drone is still there but not bad. it gives a amazing tone unlike any focus I've seen. if anyone else knows of a way to fully get rid of the drone it would be much appreciated.

 

[Nick.ggggg]

Have you taken any sound clips yet? I’d love to hear it!

 

[Bloost3]

Sound clips!!


Sent from my iPhone using Tapatalk

 

[TurboGT]

Research Helmholtz resonators as well as 1/4 wave resonators and build one. Your best bet is to make an adjustable length one (or two) so that you can tune them into cancelling the frequency range that is causing your drone. Theres a lot of math involved in engineering one (including the variable of the temperature of the exhaust gases) so trial-and-error will be the best bet.

 

[junits15]

Research Helmholtz resonators as well as 1/4 wave resonators and build one. Your best bet is to make an adjustable length one (or two) so that you can tune them into cancelling the frequency range that is causing your drone. Theres a lot of math involved in engineering one (including the variable of the temperature of the exhaust gases) so trial-and-error will be the best bet.

This is the right answer, the tricky part is determining the principle frequency component of the drone that you want to cancel.

There is a lot of math involved to do it perfectly, but you can just find the frequency and make the resonator 1/4 wavelength and it will work.

Then make the ends adjustable and tweak until it’s right.

 

[Mzdrati]

That's a pretty ambitious project. Good for you for taking it on, and best of luck.

You can see why these are more than just bent pipes, and are engineered for sound, performance, and longevity.

 

[triumph202]

You can get phone apps that act as a spectrum analyser and will give you sound frequency vs amplitude.

PS: Trying to eliminate drone using mufflers/ resonators can work out very expensive and may not eliminate the problem. Also check the system isn't expanding in length with heat and touching somewhere on the body (especially when the engine rotates on it's mounts when accelerating.) I had that problem on a vehicle.

 

[Subway]

So are there sounds to be heard here?

 

[michael_ST]

I traded a local ST guy my stock exhaust for his roush exhaust....it’s so awful. WOT it sounds really good, but highway drive it drones worse that any exhaust I’ve ever heard. I would love to find a way to eliminate that.

 

[TurboGT]

I traded a local ST guy my stock exhaust for his roush exhaust....it’s so awful. WOT it sounds really good, but highway drive it drones worse that any exhaust I’ve ever heard. I would love to find a way to eliminate that.

I really wonder how much drone is caused by the system itself vibrating like a tuning fork. What i mentioned above is known to work, but has anyone out there tried attaching mass dampers to the pipe itself to see if it helps?

One i know of is Mopar #52103612AA. Might take a couple of them to absorb the vibrations of the pipe itself. Anyone care to try?

 

[mitch808]

Add a muffler for an easy fix. The biggest one you can fit.

Or build a helmholtz resonator as suggested. Which doesn't require too much thinking, just logistics IMO. There are free apps for getting the frequency of the drone that bothers you. You need a temp probe for the exhaust gas temp, and there are calculators on the web to help you when you have all that detail.

Frankly option 1 will solve it the fastest. Some of the most positive reviewed exhausts for the ST, are Milltek and Scorpion. Both use a large muffler at the axleback area, and optional resonators. Perhaps something to do with EU laws..